Norway; (3) Australian Antarctic Division, Climate processes and change, Kingston, Australia; (4) National University of Ireland, Experimental physics, Kildare, Ireland; (5) Istituto de Astronomia y Física del Espacio, Buenos Aires, Argentina; (6) Utah State University, Center for Atmospheric and space sciences, Logan, United States of America

The International Network for the Detection of Mesoscale Change (NDMC, http://wdc.dlr.de/ndmc) is a global program with the mission to promote international cooperation among research groups investigating the mesoscale region (80-100 km) with the goal of early identification of changing climate signals.

NDMC is contributing to the World Climate Research Program, WCRP.

Measurements of the airglow at the mesopause altitude

region (80-100km) from most of the European NDMC stations including spectro-photometers and imagers allow monitoring atmospheric variability at time scales comprising long-term trends, annual and seasonal variability, planetary and gravity waves and infraspheric signals. The measurements also allow validating satellite-based measurements such as from the TIMED-SABER instrument.

Examples will be presented for airglow measurements and for related atmospheric dynamics analysis on the abovementioned spatio-temporal scales and comparisons with satellite-based instruments as well as with LIDAR soundings. Focus will be on climate signals in the mesopause region.

# 1109 - Understanding the Earth's changing water cycle

## ORAL PRESENTATIONS

### K-1109-01

#### Connections between water and energy: Clouds, water vapour, radiation and precipitation

G. Stephens (1)

(1) JPL, California Institute of Technology, Pasadena, United States of America

Water and energy are intimately coupled together in the Earth's climate system. Each controls the other. This talk will concentrate on atmospheric feedbacks that develop between water and energy that influence the global hydrological cycle response in a warming and moistening climate. As the planet warms, the amount the global precipitation increases is determined by the increased emission from the atmosphere that is mostly controlled by the increases to water vapor. The increases to water vapor, especially that transported to the upper atmosphere by convection, fundamentally affects the radiation balance both directly through the influence the clear-sky emission and by enhancing the absorption of radiation by the upper tropospheric clouds that develop as a consequence of the moistened upper troposphere. Thus feedbacks develop between radiation, clouds and precipitation that influence how the global hydrological cycle responds to a warmed climate. These feedbacks, and others will be discussed in the context of both global and regional changes in the hydrological cycle.

### K-1109-02

#### Land processes and the global water cycle: Past results and upcoming CMIP6 plans

S. Seneviratne (1) ; B. Van Den Hurk (2) ; G. Krinner (3) ; H. Kim (4) ; C. Derksen (5) ; T. Oki (4)

(1) ETH, Zurich, Institute for atmospheric and climate science, Zurich, Switzerland; (2) KNMI, Model Development, De Bilt, Netherlands; (3) LGGE, Grenoble, France; (4) University of Tokyo, Global hydrology and water resources engineering, Tokyo, Japan; (5) Environment Canada, Climate research division, Toronto, Canada

Terrestrial processes play an essential role in the global water cycle, through a range of mechanisms. Soil moisture-climate interactions affect both extreme temperatures and precipitation on land (e.g. Seneviratne et al. 2010; Hurk et al. 2011, Seneviratne et al. 2013, Guilford et al. 2015) and also explain discrepancies between global-scale patterns in wetting and drying and respective trends over land (Greve et al. 2014). But recent analyses suggest that models may share common biases in their representation. Snow-climate feedbacks are also of strong relevance, but associated with substantial uncertainties (Derksen and Brown 2012, Brutel-Vuilmet et al. 2013). This presentation will provide an overview on the role of land surface exchanges in the global water cycle and on current perspectives for future research in this field. In particular, it will highlight plans for the Land Surface,

Snow, and Soil moisture Multimodel Intercomparison Project (LS3MIP) under the 6th phase of the Coupled Model Intercomparison Project (CMIP6), which will allow a better validation, assessment, and quantification of the underlying processes and feedbacks in current climate models.

#### References

Brutel-Vuilmet, C., M. Ménégoz, and G. Krinner, 2013: An analysis of present and future seasonal Northern Hemisphere land snow cover simulated by CMIP5 coupled climate models. The Cryosphere, 7, 67-80, doi:10.5194/tc-7-67-2013.

Derksen, C., and R. Brown, 2012: Spring snow cover extent reductions in the 2008-2012 period exceeding climate model projections. Geophys. Res. Lett., 39, L19504, doi:10.1029/2012GL053387.

Guillod, B.P., B. Orlowsky, D.G. Miralles, A.J. Teeling, and S.I. Seneviratne, 2015: Reconciling spatial and temporal soil moisture effects on afternoon rainfall. Nature Communications, 6, 6443.

Greve, P., B. Orlowsky, B. Mueller, J. Sheffield, M. Reichstein, and S.I. Seneviratne, 2014: Global assessment of trends in wetting and drying over land. Nature Geoscience, 7, 716-721, doi: 10.1038/NGEO2247.

Seneviratne, S.I., T. Corti, E.L. Davin, M. Hirschi, E.B. Jaeger, I. Henné, B. Orlowsky, and A.J. Teeling, 2010: Investigating soil moisture-climate interactions in a changing climate: A review. Earth-Science Reviews, 99, 3-4, 125-161, doi:10.1016/j.earscirev.2010.02.004.

Seneviratne, S.I., M. Wilhelm, T. Stanelle, B.J.J.M. van den Hurk, S. Hagemann, A. Berg, F. Cheruy, M.E. Higgins, A. Meier, V. Brovkin, M. Claussen, A. Ducharne, J.-L. Dufresne, K.L. Findell, J. Ghattas, D.M. Lawrence, S. Malyshev, M. Rummukainen, and B. Smith, 2013: Impact of soil moisture-climate feedbacks on CMIP5 projections: First results from the GLACE-CMIP5 experiment. Geophys. Res. Lett., 40 (19), 5212-5217.

van den Hurk, B., M. Best, P. Dirmeyer, A. Pitman, J. Polcher, and J. Santanello, 2011: Acceleration of Land Surface Model Development over a Decade of Glass. Bull. Am. Meteorol. Soc., 92, 1593-1600, doi:10.1175/BAMS-D-11-00007.1

### K-1109-03

#### Changes in continental water cycle and extreme events

O. Zolina (1)

(1) Joseph Fourier University, Le laboratoire de glaciologie et géophysique de l'environnement, Grenoble, France

Ongoing and projected changes in continental water cycle are closely connected with extreme events which provide specific mechanisms of water cycle changes. We are going to address observed variability and change in continental water cycle in the context of climate extremes. Although hydroclimate extremes result from many factors that sometimes act together, water is a central component of these extremes via either its excess or scarcity. The major factor underlying hydroclimate extremes is precipitation, closely associated with flooding and droughts resulting from long dry periods and substantial water deficits over large regions. Among the major problems of changes in water cycle associated with extremes we will consider changes in temporal structure of precipitation
or precipitation timing. Over last several decades both wet and dry periods have become longer in several large European regions, specifically in Central and Eastern Europe. This effect is not associated with changes in the number of wet days but, rather, with the grouping of wet days into prolonged wet and dry periods, increasing the likelihood of floods and droughts, respectively. Another critical problem for accurate quantification of the impact of extremes on water cycle is scaling of precipitation. Representation of the impact of precipitation extremes on the water cycle strongly depends on spatial and temporal scales resolved by observational networks and models. With given resolutions we only partly capture the effect of extreme events in changes of hydrological cycle. We will demonstrate potential of very dense observational networks for accurate estimation of the role of hydroclimate extremes in continental scale water cycle. We will also consider the role of atmospheric moisture transport in forming extreme precipitation in different midlatitudinal regions, analyzing mechanisms associated with cyclone activity and transports by the mean flow. Finally, we will discuss the requirements for data characteristics and model resolution for accurate estimation of the strongly localized nature of hydroclimate extremes and their impact on continental water cycle.

# 1109-POSTER PRESENTATIONS

## P-1109-01

### Congo Basin precipitation : understanding sources and variability

D. Dyer (1) ; D. Jones (1) ; D. Neone, (2) ; J. Nusbaumer, (3)
(1) University of Toronto, Department of physics, Toronto, Canada; (2) Oregon State University, College of earth, ocean, and atmospheric sciences, Corvallis, United States of America; (3) University of Colorado, Department of atmospheric and oceanic sciences, Boulder, United States of America

The Congo Basin is an extremely interesting and dynamic hydrological region, spanning six countries and a range of ecosystems. It is home to over 75 million people who rely on forest and freshwater resources along with agriculture for subsistence. It has the second largest continuous rainforest in the world, the second largest river by discharge and is one of the main ways of deep convection in the tropics. In many ways the Congo Basin is similar to the Amazon but in comparison is greatly understudied. According to the IPCC 5th Assessment Report agreement between models in CMIP3 and CMIP5 ensembles is low in this region. CMIP5 shows better agreement in boreal winter and worse agreement in boreal summer. Unlike other African regions, there have not been dedicated measurement campaigns, such as the African Monsoon Multidisciplinary Analysis, and the availability of rain gauge and other in situ observations is sparse. An understanding of the current seasonality and variability in Congo Basin precipitation is a step towards good predictions of changes in the future.

We examine the relative importance of vapor from neighbouring regions to precipitation variability in the Congo Basin, using a new water tracer capability in the Community Earth System Model (CESM1.2), in which water is tagged in the atmosphere in geographically defined regions. In this approach, regional vapor tracers are tracked through small changes until the vapor is precipitated. We employ a small ensemble using CESM1.2 in an AMIP configuration, and results are compared with the ECMWF Interim reanalysis, the Global Precipitation Climatology Project data set and the Climate Research Unit rainfall data set. The tagged water results are compared to results from a stable isotope ensemble using the same model setup, where water isotopes are tagged as they enter the atmosphere. The results from the stable isotope enabled model are evaluated using the International Atomic Energy Agency's Global Network of Isotopes in Precipitation dataset.

A recycling ratio is calculated for the basin during dry and rainy seasons, showing a consistently high ratio with very high recycling during the dry seasons. Although local moisture evaporation does play a large role in the bulk of Congo Basin precipitation, the variability of local moisture sources cannot necessarily account for the total variability or seasonality. We find that the southern and western Indian Ocean are significant sources, providing

important contributions to variability in Congo Basin precipitation. We find that the vertical structure of moisture flux convergence is important in determining the rainy seasons and is potentially an explanation for the signature of the vapor source of Congo Basin precipitation. Using tagged vapor and also tagged water isotopes to examine atmospheric vapor, important processes which characterise Congo Basin precipitation can be explored. This will contribute to a better understanding of how precipitation in the region may change in the future.

## P-1109-02

### Typhoon Bophia: Impact of an extreme tropical cyclone on the atmospheric water and energy cycle

T. Garot (1) ; H. Brogniez, (1) ; N. Viltard, (1)
(1) Laboratoire Atmosphère Milliennes Observations Spatiales, Guycantour, France

In a context of global warming, theory and modeling predict that hurricane intensity should increase with increasing global mean temperatures. It is therefore important to better study the extreme cyclones, which could become the average case. Typhoon Bophia formed on November 25 and dissipated on December 9, 2012. It was the strongest tropical cyclone to ever hit the southern Philippine island of Mindanao, making landfall as a Category 5 super typhoon with winds of 280 km/h. Bophia caused substantial damage to Mindanao, leaving behind hundreds of thousands of homeless and more than 500 fatal casualties. During the life cycle of the typhoon, the Megha-Tropiques satellite provided 2 to 5 sampling of the tropical atmosphere per day, thanks to its low inclination orbit (20°). At that time, the two microwave radiometers SAPHIR and MADRAS were both performing measurements thus giving the opportunity to investigate (1) how the typhoon impacted the atmospheric humidity of its environment and (ii) the temporal evolution of its rain field. For this purpose, three different levels of upper tropospheric humidity retrieved from SAPHIR, rain rates and releases of total latent heat estimated from MADRAS were monitored along the storm track. We will discuss the mean behavior of the typhoon that shows strong lagged oscillations of humidity and convection during its life cycle and deepens its spatial asymmetries and their relationship with the mean state of the atmosphere. This analysis is compared with the use of the tracking algorithm TOOCAN that allows to study how each individual convective clusters contributed to the life cycle of the typhoon.

## P-1109-03

### Cold/Shoulder Season Precipitation Near 0°C

P. Groisman (1) ; S. Gulev (2) ; O. Zolina (3) ; R. Vose (4) ; I. Hanssen-Bauer (5) ; O. Bulygina (6)
(1) UCAR at NOAA National Climatic Data Center, Asheville, North Carolina, United States of America; (2) RAS P.P. Shirshov Institute for Oceanology, Moscow, Russia; (3) Joseph Fourier University, Le laboratoire de glaciologie et géophysique de l'environnement, Grenoble, France; (4) NOAA National Climatic Data Center, Asheville, United States of America; (5) Norwegian Meteorological Institute, Oslo, Norway; (6) Russian Inst. For Hydrometeorological Information, Obninsk, Russia

Small changes in atmospheric conditions lead to major changes in the types or amount of near-0°C precipitation. For example, if near-surface temperatures are slightly above (below) 0°C, rain or wet snow (snow) occurs; if a slightly above-freezing inversion occurs (or not) aloft, freezing rain (snow) can reach the surface. It also needs to be recognized that solid precipitation amounts near 0°C (such as wet snow) can be the highest in a winter storm.

With global climate change in the extratropics, the 0°C isotherm will not disappear and associated precipitation events will continue to occur. Rain should fall farther up slope in mountainous regions. This is thereby increasing the risk of flooding. Alterations in temperatures, storm intensity and track will alter the likelihood and occurrence of near-0°C precipitation including freezing rain. Weakening of the atmospheric circulation in the extratropical regions may lead to more polar jet stream meandering that can lead to more persistent near 0°C events. The overall warming, together with a larger influx
Assessment of climate transformation
in Belarus according to the COSMO-CLM
model simulations

I. Partasenok (1); B. Geyer (2); V. Melnik (1)

(1) Hydromet, Minsk, Belarus; (2) Institute of Coastal Research, System analysis and modelling, Geesthacht, Germany

According to climatic investigations deviations of annual temperature have increased during last decades in Belarus. The period of significant transformation of the temperature regime has been observed since 1970s, and rapidly since 1989.

We used simulations of the COSMO model in CLimate Mode (COSMO-CLM or CCLM) for detailed assessment of climate transformation in Belarus. This is a nonhydrostatic regional climate model developed from the Local Model (LM) of the German Meteorological Service by the CLM-community.

The coastDatIl dataset was produced with the COSMO-CLM at the Institute of Coastal Research of HZG to give a consistent and homogeneous database mainly for assessing weather statistics and climate changes since 1948, e.g., in frequencies of extremes for Europe. The simulation was done for 1948 to 2012 and a horizontal grid size of 0.22 degree in rotated coordinates. Global reanalysis data of NCEP1 were used as forcing.

The observed gridded data (E-Obs) was applied in the study for estimation of adequacy of the model simulations. We used the E-Obs v.10.0 gridded dataset (European Climate Assessment & Dataset) for the period of 1950-2012 as an European daily high-resolution gridded dataset the surface temperature and precipitation data.

We calculated means of seasonal temperature and precipitation over Belarus for 1955-2012 period. The calculations of temperature showed differences in the coastDatIl and E-Obs varied within 0.6-2 oC depending on season. The largest deviations were obtained in winter and consist of -7-2.0 oC, in spring differences were as 0.8-1 oC, in summer were obtained the smallest deviations within 0.6-0.8 oC and in autumn they were about 1.0-1.3 oC. Yearly means differ for both period on 0.9 oC. During the year the E-Obs values were higher than coastDatIl except summer when values derived from CCLM exceed the observed ones. Analysis of min/max values of seasonal temperature proved smoothed course of the temperature with less amplitude in CCLM.

Calculated differences of annual sums of precipitation were not significant and lied within 7%. But differences of seasonal sums varied from 10 to 20 %, especially in summer season when difference was about 50 %. It could be explained as an incorrect calculation of precipitation forced by convective process.

Analysis of annual temperature trends according to coastDatIl showed statistically significant increasing of temperature over entire territory of Belarus: from 0.22 oC per decade on the West to 0.3 oC per decade of the East of the country. Trends of annual precipitation showed remarkable increasing (up to 12 mm per decade) in the North and North-East part of the Belarus but in the central and southern parts of the country sums of annual precipitation varied within norm.

Physical properties and evolution of
mesoscale high cloud systems

S. Protopapadaki (1); C. Stubenrauch (1); A. Feofilov (1)

(1) Laboratoire de Météorologie Dynamique, Université de Paris 6, Paris, France

Representing about 40% of the Earth's total cloud cover, clouds in the upper troposphere play a crucial role in the climate system by modulating the Earth's energy budget and heat transport. These clouds often form mesoscale cloud systems extending over several hundred kilometres. Ubiquitous cirrus (semi-transparent ice clouds in the upper troposphere) evolve as the outflow of convective and frontal systems or form in cold air supersaturated

of the water vapour in the winter atmosphere from the oceans (including ice-free portions of the Arctic Ocean) will allow more water vapour in the winter atmosphere that can increase the amount of near-0°C precipitation. And, near-0°C temperatures should generally move poleward and arrive at many locations earlier in spring or later in autumn. This could potentially affect the seasonal cycle of near-0°C precipitation.

Despite significant progress in addressing near-0°C precipitation, it remains a challenging issue. Kunkel et al. (2013; Bull. Amer. Meteorol. Soc.) indicated that freezing precipitation was associated with the lowest level of understanding for both detection and attribution amongst several types of hazardous weather conditions affecting the U.S.

The overall issue of near 0°C precipitation is linked with several phenomena. These include blizzards (just snow), rain-on-snow (both phases with a particularly importance of the precipitation interaction with pre-existed snowpack), and freezing rain and drizzle (just liquid). The specific hazards associated with these events include: Heavy snowfall/rainfall transition around °C, Blizzards, Rain-on-snow events, Freezing rain and freezing drizzle, and Ice load on infrastructure.

Our presentation will overview what we know and what we do not know about changes in these phenomena and formulate major tasks to advance in understanding of near-0°C precipitation, its changes, and impact.

Current and future changes in precipita-
tion and its extremes across wet and dry
regions

CL. Liu (1); R. Allan (1)

(1) Department of Meteorology, University of reading,
Reading, united Kingdom

Global warming is expected to enhance fluxes of fresh water between the surface and atmosphere, causing wet years to become wetter and dry years drier, with serious implications for water resource management. Defining wet and dry regions as the upper 30% and lower 70% of the precipitation totals across the tropics (300s-300N) each month we combine observations and climate model simulations to understand changes in the wet and dry extremes over the period 1850-2100.

Observed decreases in precipitation over the driest tropical land (1950-2010) are also simulated by coupled atmosphere-ocean climate models (-0.3%/decade) with trends projected to continue into the 21st century. Discrepancies between observations and simulations over the wettest land regions since 1950 are explained by decadal fluctuations in El Niño southern oscillation, the timing of which is not represented by the coupled simulations. When atmosphere-only simulations are instead driven by observed sea surface temperature they are able to adequately represent this variability over land.

By considering changes in the intensity distribution of precipitation, we find that global distributions of precipitation trends are dominated by spatial changes in atmospheric circulation. Unforced variability appears to dominate trends for the present day but land-surface feedbacks and secular changes in atmospheric circulation patterns become increasingly important into the future. Projected increases in extreme precipitation with warming over land are not diagnosed for the present day due to these dynamical influences which indicate that natural variability over land is not a good proxy for future climate change.

Nevertheless, the tendency for the wettest part of the
tropical circulation to become wetter (precipitation
increases with warming) by 3%–K over wettest tropical
ocean grid points) and the driest part of the atmospheric
circulation to become drier (precipitation decreases of
-2% /K over the driest tropical land grid points) is a robust
result that emerges over the 21st century in response
to the substantial surface warming. This indicates that
enhancement in seasonality and wet and dry extremes
(flooding and drought) may be anticipated over the coming
century.
with water. Both their evolution with climate change and their feedback can only be reliably estimated if these cloud systems are adequately represented in climate models. Only satellite instruments are able to give a picture as a whole of these systems. IR sounders are observing our planet since 1979, with improvements in spectral resolution: from the TIROS-N Operational Vertical Sounders (TOVS) onboard the NOAA polar satellites through the Atmospheric InfraRed Sounding (AIRS) onboard Aqua since 2002, and to the InfraRed Atmospheric Sounding Interferometer (IASI) on board the MetOp platforms since 2006. The good spectral resolution of these instruments allows reliable cirrus identification, both from day and night-time observations. For this study we have developed a novel method to describe mesoscale high cloud systems, taking into account their horizontal extent. The occurrence of convection within these systems will be estimated by using cloud emissivity and a clustering method. This allows a distinction between in situ cirrus and cirrus linked to convective or frontal systems. The vertical extent of these cloud systems, essential for determining the energy balance at the Earth surface, can only be determined from active instruments (CALIPSO lidar and CloudSat radar synchronous with AIRS). This data set will be explored and distributed within the framework of the GEWEX Process Evaluation Study on Upper Tropospheric Clouds and Convection (UTCC PROES).

We will relate the horizontal extent of the anvil to the convective strength of the system and we will present first results on the variability of high cloud systems with their surrounding atmosphere. Analyzing the evolution and properties of mesoscale cloud systems as a whole and their role in generating cirrus clouds will be a major advancement in climate studies, also giving a new impulse in climate model evaluation.

## P-1109-07

### Long-term changes in snowfall over Japan and its regionality

H. Takahashi (1) ; S. Sugimoto (1)

(1) Tokyo Metropolitan University, Tokyo, Japan

We examined the long-term changes in snowfall over Japan for recent 50 years, using observational data and a regional climate model.

Climate change can significantly influence the snowfall on the Japan Sea side of Japan because the seasonal surface air temperature is higher than 0 deg C in northern winter. The side of snowfall regions on Earth. These heavy snowfalls are a consequence of the northwestern flow of the Asian winter monsoon from Eurasia and the region's windward (northwestern side) position along Japan's northeast-southwest trending central mountain range. Two main factors influence precipitation over the Japan Sea side. One is the activity of cold and dry northwestern winds of the Asian winter

monsoon, and the other is sensible and latent heat fluxes on the Japan Sea, which are strongly associated with the sea surface temperature (SST).

The snowfall amount can be influenced by total precipitation amount and ratio of snowfall amount to the total precipitation. Total precipitation is modulated by many factors. On the other hand, the ratio of snowfall amount to the total precipitation is basically due to surface air temperature. This was investigated the both factors, focusing on regional difference of the long-term changes.

Results showed that snowfall has drastically changed over the Sea of Japan side of Japan around late 1980's. Concurrent with the drastic change in snowfall, surface air temperature has dramatically increased. However, the drastic changes in snowfall was unclear over the some regions, which was modulated by the total precipitation changes. The regionality of long-term changes in snowfall will be discussed.

## P-1109-08

### Analysis of freezing rain occurrence over Eastern Canada using regional climate model simulations

J. Thériault (1) ; É. Bresson (2) ; M. Cholette (1) ; D. Paquin (2) ; R. Laprise (1) ; R. De Élia (2)

(1) Université du Québec, Earth and Atmospheric sciences, Montréal, Canada; (2) Ouranos, Montreal, Canada

Winter storms can lead to many types of precipitation at the surface when the temperature is around 0°C. Freezing rain is the most damaging precipitation type produced during these storms. Its occurrence is associated with four atmospheric conditions leading to a temperature inversion associated with temperatures >0°C aloft and subfreezing temperature near the surface. The overall goal of this study is to investigate the changes in the occurrence of freezing rain with our changing climate using regional climate model outputs. In particular, a study of the occurrence of freezing rain is conducted with climate simulations produced by the Canadian Regional Climate Model 5 (CRCM5) over Eastern Canada. This is achieved using existing empirical techniques commonly used to solve for the various winter precipitation types produced during storms. These techniques are based on the vertical temperature structure that affects strongly the type of precipitation reaching the surface. The results show that the model resolution impacts the vertical temperature structure. This suggests that the model resolution will impact the production of freezing rain by the model. Hence, the differences in the freezing rain occurrence diagnosed at different model resolutions are summarized. Overall, this study started addressing how well regional climate models can account of winter precipitation types to assess how their occurrences will evolve in our changing climate.

# 1110 - Observing the changing ocean climate

## ORAL PRESENTATIONS

### K-1110-01

#### Climate and Ocean: past, current and future changes and variability - a challenge for observations, models and assessment

M. Visbeck (1)

(1) GEOMAR & Kiel University, Kiel, Germany

The ocean covers more than 70 % of the surface of our planet and plays a key role in supporting life on earth. It hosts the most diverse and important ecosystems, and contributes to global and regional elemental cycling. The ocean regulates our climate, and through climate, habitats are shaped that allowed humans to thrive and develop our societies. The marine system provides us with natural resources such as food, materials, substances, and energy. Furthermore, the oceans and the regional seas are essential for international trade, recreational and cultural

activities.

A growing world population with increasing levels of affluence has had a noticeable impact on the environment causing "global change". In the area of climate in particular increasing levels of greenhouse gas emissions have altered the planetary heat balanced and caused changes in both global and regional climate.

The Intergovernmental Panel for Climate Change (IPCC) most recent assessment reminds us that: "The ocean's heat capacity is about 1,000 times larger than that of the atmosphere, and the oceans net heat uptake since 1960 is around 20 times greater than that of the atmosphere." About 90% of this extra heat has been stored in the ocean. The ocean plays a crucial role in climate change, in particular in variations on seasonal to decadal time scales. One example is sea level: the addition of heat and freshwater flux from the melting glaciers and ice sheets have cause the sea level to rise. The latest IPCC gives a best estimate rate for 1961 to 2003 as 1.8 ± 0.5 mm yr-1. However, the regional differences are large and the interplay between natural climate and ocean variability and change remains a challenge for assessments.
Finally the IPCC addresses the adequacy of ocean observing systems: "Many ocean observations are poorly sampled in space and time, and regional distributions are often quite heterogeneous. Furthermore, the observational records only cover a relatively short period of time (e.g. the 1950s to the present). Many of the observed changes have significant decadal variability associated with them, and in some cases decadal variability and/or poor sampling may prevent detection of long-term trends. When time series of oceanic parameters are considered, linear trends are often computed in order to quantify the observed long-term trends; however, this does not imply that the original signal is best represented by a linear increase in time." Thus this provides an opportunity for the global ocean observing community to rise to the challenge and deliver a fit-for-purpose more integrated, more cost effective and more sustained ocean observing system.

## K-1110-02

### How do we observe and model the changing ocean physics, biogeochemistry, and ecosystems?

**N. Pinardi (1)**

(1) University of Bologna, Department of Physics and Astronomy, Bologna, Italy

The oceans play a crucial role as a climate regulator, and changing ocean physics, biogeochemistry, and biology have direct impact on human well-being through hazards and ecosystem services changes.

Long-term, globally-coordinated, and high-quality sustained ocean observations are required to understand and model the role of the ocean in the earth's climate, to monitor ocean change, and to provide initial conditions to predict the evolution of climate on scales including seasonal, decadal, and centennial. Building on national efforts, these observations are internationally coordinated through the Global Ocean Observing System and the Joint WMO-IOC Technical Commission for Oceanography and Marine Meteorology, building on the processes of a common Framework for Ocean Observing devised and adopted by the ocean observing community.

Observations and models combine to provide the best possible estimates of the present and future state of the ocean. These observations and forecasts inform decision-making about coastal protection, the marine economy, long-term changes in patterns of drought and flood, and the human consequences linked to climate change. Our confidence in the observations and models has increased over time, even as some key critical knowledge gaps remain.

## O-1110-01

### Pacific western boundary currents and their roles in climate

A. Ganachaud (1); D. Hu, (2); L. Wu, (3); W. Cai (4); G.A. Sen (5); B. Qiu, (6); A. Gordon, (7); X. Lin, (3); Z. Chen, (3); S. Hu, (2); G. Wang, (8); Q. Wang, (2); J. Sprintall, (9); T. Qu, (10); Y. Kashino, (11); F. Wang, (2); W. Kessler, (12); A. Melet (13) (1) IRFD/LEGOS, Toulouse, France; (2) Institute of Oceanology, CAS, Key laboratory of ocean circulation and waves, Qingdao, China; (3) Qingdao Collaborative Innovation Center of Marine Science and Technology, OUC, physical oceanography laboratory, Qingdao, China; (4) CSIRO, Melbourne, Australia; (5) The University of New South Wales, Australian research council (arc) centre of excellence for climate system science, Sydney, Australia; (6) University of Hawaii at Manoa, Department of oceanography, Honolulu, United States of America; (7) Lamont-Doherty Earth Observatory, Earth institute at columbia university, New York, United States of America; (8) CSIRO, Marine and atmospheric research, Melbourne, Australia; (9) Scripps Institution of Oceanography, La Jolla, United States of America; (10) SOEST, University of Hawaii, Iprc, department of oceanography, Honolulu, United States of America; (11) Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Center for earth information science and technology, Kanagawa, Japan; (12) NOAA, Pacific marine environmental laboratory, Seattle, United States of America; (13) CNES/LEGOS, Toulouse, France

Pacific Ocean western boundary currents and the interlinked equatorial ocean circulation system were among the

first to be explored by pioneering oceanographers. The widely accepted but poorly quantified importance of these currents - in processes such as the El Niño-Southern Oscillation, Pacific Decadal Oscillation and Indonesian Throughflow - has triggered renewed interest, with ongoing efforts seeking to understand the heat and mass balances of the equatorial Pacific, and possible changes associated with greenhouse-induced climate change. Only a concerted international effort through WCRP/CLIVAR will close the observational, theoretical and technical gaps currently limiting a robust answer to these elusive questions. This work will present a review of the boundary current characteristics, variations and their effects on local and remote climate, as well as their future projections.

## O-1110-02

### Preliminary results from the international South Atlantic Meridional Overturning Circulation (SAMOC) Initiative

**S. Speich (1); S. Garzoli (2); A. Piola (3); E. Campos (4)**

(1) Ecolne normale superieure, Departement de geosciences, paris, France; (2) NOAA, Aoml - phod, Miami, United States of America; (3) Servicio de Hidrografia Naval, Buenos Aires, Argentina; (4) Universidade de Sao Paolo, Instituto oceano格rafico, Sao Paolo, Brazil

Within the MOC, the South Atlantic Ocean plays a key role as a nucleus for water masses formed elsewhere and en route to remote regions of the global ocean. Because of this important interbasin exchanges, the South Atlantic Ocean is the only major ocean basin that transports heat from the pole towards the equator. However, the South Atlantic is not merely a passive conduit for remotely formed water masses. Indeed, within this basin water masses are significantly altered, by local air-sea interactions and diapycnal/isopycnal fluxes, particularly in regions of intense mesoscale activity and steep topography. These contributions have been shown to have a crucial role in the strength of the MOC in paleoceanographic and modelling studies.

The monitoring of the North Atlantic portion of the MOC has been ongoing for a decade now through the RAPID/ MOCHA/WBT'S program as well as other national and international initiatives. They all provide a scope for understanding the MOC variability in that region. Given the complex, multibasin nature of the MOC, achieving a more complete understanding of its behaviour and changes requires a more comprehensive observing system, one that extends across neighbouring ocean basins as the one we are developing for the South Atlantic within the CLIVAR SAMOC initiative.

In this presentation, we will discuss the preliminary results on estimates of the daily MOC strength at 35'S during a ~20 month long pilot array of mooring as well as model outputs and Argo data. The MOC variability show to be as large as that at 26N, with both eastern and western boundary flows contributing equally to the variance.

The full array was re-established in the fall of 2013 in collaboration with France, Brazil, Argentina and South Africa.

## O-1110-03

### Exceptional 20th-Century slowdown in Atlantic Ocean overturning circulation

S. Rahmstorf (1); J. Box, (2); G. Feulker, (1); M. Mann, (3) A. Robinson, (4); S. Rutherford, (5); E. Schaffernicht, (1) (1) Potsdam Institute for Climate Impact Research, Potsdam, Germany; (2) Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark; (3) Pennsylvania State University, University Park, United States of America; (4) Universidad Complutense de Madrid, Madrid, Spain; (5) Roger Williams University, Bristol, United States of America

Possible changes in Atlantic meridional overturning circulation (AMOC) provide a key source of uncertainty regarding future climate change. Maps of temperature trends over the twentieth century show a conspicuous region of cooling in the northern Atlantic. Here we present multiple lines of evidence suggesting that this cooling may be due to a reduction in the AMOC over the twentieth century and particularly after 1970. Since 1990 the AMOC seems to have partly recovered. This time evolution is
consistently suggested by an AMOC index based on sea surface temperatures, by the hemispheric temperature difference, by coral-based proxies and by oceanic measurements. We discuss a possible contribution of the melting of the Greenland Ice Sheet to the slowdown. Using a multi-proxy temperature reconstruction for the AMOC index suggests that the AMOC weakness after 1975 is an unprecedented event in the past millennium (p>.99). Further melting of Greenland in the coming decades could contribute to further weakening of the AMOC.

Reference: Rahrmorf et al, Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation, Nature Climate Change (in press)

## O-1110-04

### Variability of the Meridional Overturning Circulation observed since 1993 across the A25-OVIDE section in the North Atlantic subpolar gyre, and its impact on the CO2 physical pump

P. Lherminier (1); N. Daniault, (2); FF. Perez, (3); P. Zunino, (1); H. Mercier (4); A. Sarafanov, (5); F. Gaillard (1); P. Morin (6); A. Riios (3); D. Desbruyeres (7); A. Falina (5); B. Ferron (4); T. Huck (8); V. Thierry (1); Ml. Garcia-Ibanez (3)

(1) Ifremer, Laboratoire de Physique des Oceans, PLOUZANE, France; (2) Université de Bretagne Occidentale, Laboratoire de physique des oceans, BREST, France; (3) Instituto Investigaciones Marinas (CSIC), Departamento de oceanografía, VIGO, Spain; (4) CNRS, Laboratoire de physique des oceans, PLOUZANE, France; (5) P.P. Shirshov Institute of Oceanology, Moscow, Russia; (6) IPEV, Scientific direction, PLOUTCHAM, France; (7) National Oceanography Centre, Southampton, United Kingdom; (8) CNRS, Laboratoire de physique des oceans, Brest, France

The meridional overturning circulation (MOC) transports heat from the subtropics to high latitudes and hence plays an important role in the Earth's climate. A region crucial for the MOC is the northern North Atlantic and the adjacent Nordic Seas, where waters transported northwards in the MOC upper limb progressively cool, gain density and become less buoyant. The MOC is then forced to lower the upper limb. Here we will discuss the variability of the subpolar gyre circulation, the MOC and heat transport as quantified from a joint analysis of hydrographic and velocity data from eight repeats of the Greenland to Portugal OVIDE section (1997-2014), satellite altimetry and ARGO float measurements. For each repeat of the OVIDE section, the full-depth absolute circulation and transports were assessed using an inverse model constrained by ship-based altimetry and hydrographic data and by an overall mass balance. The obtained circulation patterns revealed remarkable transport changes in the whole water column and evidenced large variations (up to 50% of the lowest value) in the magnitude of the MOC computed in density coordinates (MOCo). The extent and timescales of the MOCo variability in 1993-2014 were then evaluated using a monthly MOCo index built upon altimetry and ARGO data at the OVIDE section location. The MOCo index, validated by the good agreement with the estimates from repeat hydrographic surveys, shows a large variability on monthly to decadal time scales, with an inter-annual variability from less than 15 Sv to about 25 Sv (1 Sv = 1,000,000 m3s⁻¹). The heat transport estimated from the repeated hydrographic OVIDE sections varies between 0.29 and 0.70 ± 0.05 PW and is linearly related to the MOCo intensity.

The uptake of atmospheric carbon dioxide in the subpolar North Atlantic Ocean declined rapidly between 1990 and 2006. This reduction in CO2 uptake was related to warming at the sea surface, which—according to model simulations—coincided with a reduction in the Atlantic MOC. Here, we use the observed oceanic transport of volume, heat and carbon dioxide to track the CO2 uptake in the subtropical and subpolar regions of the North Atlantic Ocean over the past two decades. We separate anthropogenic carbon—derived from human activities—from natural carbon by assuming that the latter corresponds to a pre-industrial atmosphere, whereas the remaining is anthropogenic. We find that the uptake of anthropogenic carbon dioxide occurred almost exclusively in the subpolar gyre. In contrast, natural carbon dioxide uptake—which results from natural Earth system processes—dominated in the subpolar gyre. We attribute the weakening of contemporary carbon dioxide uptake

between 1997 and 2006 in the subpolar North Atlantic to a reduction in the natural component. We show that the slowdown of the MOC was largely responsible for the reduction in carbon uptake, through a reduction of oceanic heat loss to the atmosphere, and for the concomitant decline in anthropogenic carbon dioxide storage in subpolar waters. To understand the mechanisms controlling the variability of the transport of anthropogenic carbon (Tcant) across the subpolar gyre, we decomposed it according to the net, the diapycnal and the isopycnal circulation. The diapycnal component is found to be the main driver of the Tcant variability. From this analysis, we propose a simplified estimator for the variability of Tcant based on the intensity of the MOCo and on the difference of anthropogenic carbon dioxide concentration between the upper and lower limb of the MOCo (ΔCant). This estimator shows a good consistency with the diapycnal component of Tcant, and helps to disentangle the effect of the variability of both the circulation and the Tcant increase on the Tcant variability. We find that ΔCant keeps increasing over the past decade, and it is very likely that the continuous Tcant increase in the water masses will cause an increase in Tcant across the subpolar North Atlantic Ocean at long timescale. Nevertheless, at the timescale analyzed here (1997-2010), the MOCo controls the Tcant variability, blurring any Tcant trend.

## O-1110-05

### Oxygen Minimum Zone (OMZ) dynamics in the context of the ocean deoxygenation: the case off Peru from the AMOP «Activities of research dedicated to the Minimum of Oxygen in the eastern Pacific» project

A. Paulmer (1); B. Dewitte (2); C. Maes (3); M. Bretagnon (2); V. Garzon (4); F. Campos (5); F. FG. Augusto (6); K. Mosquera (7); O. Vergara (2); C. Barus (2); L. Coppola (8); O. Depretz-De-Gesincourt (9); E. Garcia-Ribledo (10); J. Grelet (11); S. Illig (2); I. Montes (7); N. Leblond (12); A. Schlichs (13); J. Quispe (14); J. Sudre (3)

(1) LEGOS, SYSCO2 team, TOULOUSE, France; (2) LEGOS, Toulouse, France; (3) IRD-CNRS-Ifremer-UBO, Laboratoire de physique des oceans, Plouzane, France; (4) CNRS, LEGOS, Toulouse Cedex, 1; France; (5) UNA-CAR, Peru; (6) where H. LIMA, Peru; (7) IGP, LIMA, Peru; (8) OOV, VILLEFRANCHE/S-MER, France; (9) Parc Instrumental DT-INSU/CNRS, PLOUZANE, France; (10) University of Aarhus, AARHUS, Denmark; (11) US IMAGO, PLOUZANE, France; (12) CNRS, Lov, Villefranche sur mer, France; (13) GEOMAR, Kiel, Germany; (14) IMARPE, CALLAO, Peru

### Oxygen Minimum Zones (OMZs), defined as suboxic O₂ > 20 L)

Surface Upwelling and mainly associated with Eastern Boundary Upwelling Systems (EBUS), would contract and expand during cold and warming periods, respectively. In the current context of the ocean deoxygenation, OMZs are known to play a key role on the evolution of climate (greenhouse gases) and on the ecosystems and fisheries (nitrogen loss, respiratory barrier, sulfidic events) at both local and global scales. The objective of the AMOP project «Activities of research dedicated to the Minimum of Oxygen in the eastern Pacific» is to provide an estimate of physical and biological processes contributing to the O₂ budget off Peru. The central hypothesis is that the physical and biogeochemical O₂ contribution to the OMZ maintaining and variability depends on the characteristics of the different OMZ layers, where the oxycline behaves as an engine of an intense but intermittent biogeochemical and ecosystem activity. The project is focused in one of the most intense areas allowed OMZs associated with the most productive upwelling system (10 % of the world fisheries), the Peruvian OMZ. The trans-disciplinary approach is based on a cruise that took place in January-February 2014 off Peru and that consisted in 8 fixed stations (~54 h) on 3 transects at 7's, 12's and 14's with the RV Atalante. The cruise also benefited from experimental development (instrumentation, sensors: argo-floats experiments; drifting lines; a trimaran dedicated to ocean-atmosphere measurements). AMOP has also led to the deployment of the first long term (2013-2014) subsurface mowing off Peru providing unprecedented information of the OMZ variability at diurnal to intraseasonal timescales, and invaluable data for the validation of a high resolution regional ocean-atmosphere-biogeochemistry coupled modeling platform under development within the project. This French-Peruvian-German project involving 5 other countries (~90
participants) is viewed as one of the main pilot projects of the SOLAS Mid Term Strategy Initiative on OMZ-EBUS. In this presentation, preliminary results of the project will be presented both on observations and modeling, illustrating current challenges for the investigation of OMZ dynamics in Eastern Boundary current systems.

1110-POSTER PRESENTATIONS

P-1110-01

Recent changes and trends of the upwelling intensity in the Canary Current Upwelling System

A. Benazzouz (1) ; K. Hilmi (2)

(1) Institut National de Recherche Halieutique, Département océanographie, Casablanca, Morocco; (2) Institut National de Recherche Halieutique, Département océanographie, Casablanca, Morocco

A summary of current knowledge for the quantification of the upwelling intensity from wind and SST is provided on the Canary Current Upwelling System (8°N–43°N) from 1982 to 2011. Statistical analysis of trends and seasonal changes of the upwelling activity are carried out in this work. Linear trends in upwelling intensity are estimated from both atmospheric forcing (wind stress) and thermal oceanic response (SST), both derived from satellite data, with a particular focus on the Cap Ghar of the moroccan area (30.5°N). The results indicate different spatial trends in the upwelling favorable winds and an apparent increasing coastal warming associated with intensification of winds at the regional scale off Northwest Africa is found.

P-1110-02

Long term marine time-series expose underlying climate-driven changes in South America during the last 40 years

A. Arias (1) ; E. Alberdi, (2) ; R. Freije, (3) ; J. Marcovecchio, (1)

(1) Argentine Institute of Oceanography (IADO), CONICET, Bahia Blanca, Argentina; (2) Argentine Institute of Oceanography (IADO), CONICET, Bahia Blanca, Argentina;

(3) Universidad Nacional del Sur, Chemistry, Bahia Blanca, Argentina

Climate Change is creating a dynamic of continuous changes in ecosystems. Generally, the expected consequences of these changes are global; however, the occurrence of extreme events and specific environmental problems are usually local or regional phenomenon. One of the keys to uncover climate-driven changes are the long term time-series of observations. While there are a number of long-term biological time-series on land, there are relatively few in marine environments. This is highlighted by the fact that the Intergovernmental Panel on Climate Change (IPCC) noted 28586 significant biological changes in terrestrial systems, but only 85 from marine and freshwater systems. The present research deals with this gap in the state of the art, focusing in an area which holds scarce to null long-term research on ocean observation and climate driven changes: the South Atlantic Ocean. From the results of the analysis of up to 40 years of oceanographic physicochemical variables measured at the Bahia Blanca Estuary (Dissolved Oxygen, pH, Chlorophyll, Phaeopigments, Temperature, Salinity, NH4, Particulate Organic Matter, NO2, NO3, Phosphorous, etc.) unknown underlying trends were uncovered. In order to test the variables trend throughout several time-scales, the continuous wavelet transform (CWT) was used to divide the continuous time function into axisets. Moreover, the use of Cross Wavelet Correlation (CWC) allowed to light the relationship between the variables throughout different time-scales. After that, a correlation analysis which linked the ocean observations to biological documented changes was assessed. As result, novel hypotheses were raised in the field of phytoplankton and zooplankton assemblages climate-driven control, crustaceans catches and fisheries recruitment. For instance:

* "climate-driven variations in ocean Temperature, pH, DO and Salinity can restrict the growth of the phytoplankton assemblages, leading to other factors (i.e., grazing) the size control of the cells"

* "low interannual variability of water temperature and water salinity favours higher fishing yields and vice versa»

Undoubtedly, these findings will strengthen the theory which propose climate-driven changes at marine coastal ecosystems as a consequence of global climate change and will be of high relevance for the international dialogue on "anthropogenic vs. climate-induced changes" over the oceanic ecosystems.

P-1110-03

Past and future seasonal changes in Sea Surface Temperature in the Western English Channel as derived from satellite data and CMIP5 multimodel ensemble

B. L'hévéder (1) ; S. Speich (2) ; F. Gohin (3)

(1) CNRS, LMD, Paris, France; (2) Ecolne normale supérieure, Département de geosciences, paris, France; (3) Ifremer, Dyneco/pelagos, Brest, France

Seasonal changes in Sea Surface Temperature (SST) in the Western English Channel are estimated for the last decades from high-resolution satellite data, obtained by concatenating Ifremer AVHRRSST, OSTIA and ODSYSEA data over 1986-2013. Coastal waters, well separated from offshore waters by intense frontal structures, present colder SST by about 1°C in the English Channel to 2°C in the Irloise Sea in summer. A significant warming trend, concentrated in the autumn season, is highlighted. It is stronger offshore, with a SST annual mean increase of 0.32°C/decade, while it amounts to 0.23°C/decade in coastal waters, where a strong vertical mixing induced by tides and wind acts to reduce surface warming.

The performance of an ensemble of global climate models, participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5), in simulating recent seasonal changes of SST in the region is estimated. The median of CMIP5 models reproduces very well the observed SST mean seasonal cycle in offshore seas, but it less proficient in coastal waters due to model coarse resolution and absence of tidal forcing and related processes. In the Irloise Sea, the trend of the annual mean SST is relatively well simulated, albeit somewhat underestimated (0.20/ decade) and evenly distributed throughout the year.

The regional values of the annual mean SST as generated by the CMIP5 future scenarios simulations, range from 0.5°C (RCP2.6) to 2.5°C (RCP8.5) year 2100, with a seasonal modulation leading to a more intense warming in summer than in winter. This increase in SST may strongly affect marine biomes, in particular phytoplankton and algae population density and phenology in the Western English Channel.

P-1110-04

Comparing coastal and open ocean sea level variability and trend from altimetric data

A. Melet (1) ; F. Birol, (2) ; B. Meyssignac (2)

(1) CNES/LEGOS, Toulouse, France; (2) LEGOS, Toulouse, France

Since 1993, altimetry has provided an unprecedented opportunity to study sea level variability with a quasi-globa coverage. Satellite altimetry indicates that sea level has been rising fast in response to global warming, but with large regional variations. However, standard altimetric data do not allow to study sea level variability and rise close to the coast, where the socio-economic impacts of sea level rise are the greatest. Recently, along-track altimetric data have been reprocessed at LEGOS/ CTOH using algorithms adapted to coastal regions to recover information in coastal zones (this reprocessed coastal product is referred to as the XTRACK dataset here).

In this study, we first intercalibrate the along-track Topex- Poseidon, Jason-1 and Jason-2 XTRACK dataset to that distributed by AVISO to have consistent sea level data in the open ocean. Then, sea level trends are computed with the XTRACK dataset to analyse how sea level rise varies as a function of the distance to the coast. Spectral analyses are performed to assess the frequency bands for which
coastal sea level variability and open ocean variability differ.

Analyses are performed over two regions (West coast of Africa and southwest Pacific). They will be extended to the global ocean to provide a map of sea level trends over the 1993-2012 period for the coastal zones of the global ocean.

P-1110-05

Ocean regulation of atmospheric carbon dioxide: timing of atmosphere-ocean reorganization, and CO2 outgassing during last deglaciation

E. Michel (1); G. Siani, (2); A. Mazaab (1); DPN. Van (3); M. Paterne (4); N. Haddam, (1); S. Jaccard, (5); G. Isguder, (1); F. Dewilde, (1); T. Devries, (6); C. Verbruggen, (7); S. Björck, (3); C. Waebroek (8); R. Depol-Holz, (9); C. Kissel, (1)

(1) CEA-CNRS-UVSQ, Lsce-ipsl, Gif sur Yvette, France; (2) GEOPS, Université orsay paris-sud xi, Orsay, France; (3) Quaternary Sciences, Department of geology, Lund, Sweden; (4) Laboratoire des Sciences du Climat et de l'Environnement (LSE-IPSL), Cea-cnrs-UVSQ, Gif-sur-Yvette, France; (5) Institute of Geological Sciences & Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland; (6) Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, United States of America; (7) Department of Geology and Soil Sciences, Ghent university, Gent, Belgium; (8) LSE/IPSL - CNRS, Gif-sur-Yvette, France; (9) Department of Oceanography, Universidad de concepcion, Concepcion, Chile

During the last deglaciation, centennial to millennial scale large climate changes occurred with a climate decoupling between the North and South poles called the bipolar seesaw. These events, expression of the complex interaction between the ocean, the atmosphere and the cryosphere, are not well understood yet. Associated with these events, CO2 outgassing from the ocean to the atmosphere occurred. These increases in atmospheric CO2, preceding the Earth's global temperature increase, have been an important factor of the deglaciation. The Southern Ocean plays a key role in the global climate. Intermediate and bottom waters formation occurs within the Southern Ocean and it is the region where the deeper ocean and the atmosphere are connected due to low density gradient and wind driven upwelling. We present the climatic behavior of the different Southern Ocean sectors during these climatic events, with a precise time scale. Thanks to the complementary archives and skills of Lund University and IPSL researchers, we combine the terrestrial records from the few islands present, in this mainly oceanic hemisphere, with oceanic high resolution records, using volcanic tephra to obtain a robust chronology for the marine records chronology and inconsequence a common 14C age scale. This multi-proxies approach allows reconstructing robust quantitative records of temperature and wind intensity evolution. Sediment core records from the South-East Pacific sector of the Southern Ocean indicate that both temperature increase and intensification of the Southern Ocean upwelling in this area are coeval in this area as well as, within dating uncertainty of the records, with the temperature increase over the Antarctic and atmospheric CO2 increase. In the Indian sector, a terrestrial record indicates a possible delay between the break in the increase of Antarctic temperature (Antarctic cold reversal within the deglaciation) and westerly wind belt shift. In the meanwhile, ocean records indicate that the sea surface temperature increase and the intensification of the Southern Ocean upwelling preceded the decrease or shift of the Antarctic circumpolar current. Such well-dated high resolution records will allow studying leads and lags between the climatic records of different North and South latitudes events, thus establish the link between Southern Ocean and North Atlantic circulation changes. The space and time mapping of climatic changes will be compared to climate model experiments to disentangle the role of the different atmospheric and oceanic climate mechanisms of the bipolar seesaw. It is a necessary step to improve climate models that indicate a different response to fresh water discharge experiments designed to reproduce these rapid climatic events with a bipolar seesaw signature. Indeed the different models, used for future climate simulations, indicate different responses in the different sectors (Atlantic, Indian and Pacific) of the Southern Ocean for these experiments.

P-1110-06

Interannual variability of upper ocean stratification in Bay of Bengal: observational and modeling aspects

F. T S (1); P. Anant (2); C. Gnaseelaan, (2)

(1) INDIAN INSTITUE OF TROPICAL METEOROLOGY, T D DIVISION, PUNE MAHARASHTRA, India; (2) Indian Institute of Tropical Meteorology, T. s division, pune, India

The annual cycle and interannual variability of stratification in Bay of Bengal (BoB) are studied using both observations and Global Ocean Data Assimilation System (GODAS) analysis during 2003-2012. Annual cycle of stratification and SST evolves coherently (correlation coefficient is 0.85) highlighting its role on modulating air-sea interaction over this climatologically important region. Spatial distribution of stratification shows strong seasonality in ARGO observations, whereas it is highly underestimated in GODAS with highest discrepancies during fall and spring. The annual cycle of SSS in GODAS is out of phase with observations implying possible potential feedbacks. During La Niña years, SSS drop in fall and winter and are lesser than those reported during El Niño years. All these features are misrepresented in GODAS. As stratification modulates with interaction with BOB especially during El Niño and La Niña, such misrepresentation of ocean stratification may lead to improper thermocline-SST coupling in the models. The mean stratification and its interannual variability in GODAS are weaker than observed even though interannual variability in fresh water flux (P-E) is higher in GODAS. Detailed analysis of GODAS with in-situ observations reveals that upper ocean current shear (vertical) is overestimated in GODAS leading to unrealized strong mixing which is primarily responsible for the deeper penetration of surface warm and freshwater resulting weaker stratification. As GODAS is used to initialize the ocean model of the Coupled Forecasting System for seasonal prediction of Asian monsoon, proper representation of stratification is essential. This study advocates the need of accurate representation of mixing in GODAS for improved summer monsoon forecast.

P-1110-07

Methane distributions and sea-to-air fluxes in the South China Sea and the West Philippines Sea

HC. Tseng (1); CTA. Chen, (2); AV. Borges, (3); TA. Delvalls, (1)

(1) University of Cadiz, Physical Chemistry Department, Cadiz, Spain; (2) National Sun Yat-sen University, Department of oceanography, Kaohsiung, Taiwan; (3) University of Liege, Unité d'océanographie chimique, Liège, Belgium

We collected 700 water samples in the South China Sea (SCS) and 300 water samples in the West Philippines Sea (WPS), during 8 cruises from August 2003 to July 2007 in order to determine methane (CH4) distributions from surface to depths of 4250 m. The surface CH4 concentrations were above atmospheric equilibrium, both in the SCS and the WPS, with an average concentration of 4.5±3.6 and 3.0±1.2 nM, respectively. The sea-to-air fluxes were computed, showing that the SCS emits CH4 at a rate of 8.6 µmol m-2 d-1 and the WPS at a rate of 4.9 µmol m-2 d-1. In the SCS, the CH4 emissions were higher over the continental shelf (11.0 µmol m-2 d-1) than over the deep ocean (6.1 µmol m-2 d-1), owing to higher productivity and closer coupling with the sediments in the continental shelf. The SCS emited 30.1*10⁶ mol d-1 CH4 to the atmosphere and exported 1.88*10⁶ mol d-1 CH4 to the WPS during the wet season.

Both the concentrations of CH4 and chlorophyll a were higher in the 200m surface layer of the WPS, however, not correlated unlike recent reports suggesting the occurrence of CH4 production in surface oxic waters directly related to phytoplankton activity. CH4 concentrations generally decrease with depth below the euphotic zone but remain constant below 1,000 m, both in the SCS and the WPS. Some high CH4 values were observed at mid-deaths in the SCS, and were most likely attributed to the anoxic generation of CH4 or the release of CH4 from sediments, gas hydrates or gas seepage.
# 1111 - Climate variability, change and vulnerability in the Pacific, Indian and Southern Oceans

## ORAL PRESENTATIONS

### O-1111-01

#### Why should coral reefs care about ocean acidification: general consensus, misconceptions and future research priorities

R. Rodolfo-Metalpa (1); F. Houlbrèque (1); C. Payri (1)

(1) Institut de Recherche pour le Développement, Umr entropy-laboratoire d'excellence corail, Nouméa cedex, New Caledonia

Ocean acidification (OA) is one of the main threats for marine habitats, likely causing changes in biodiversity and ecosystem functions within this century. Ocean acidification might affect various physiological parameters at different stages of the animal life history, from their reproduction to larval phases and adult growth. Coral reefs, harboring a large part of the world's ocean biodiversity, will be the most affected by OA, as calcification and dissolution rates are related to seawater carbonate chemistry. Studies show a decline in net calcification rates as a result of decreasing pH and carbonate ion concentrations, and increasing dissolution rates of carbonate skeletons. This alarming general consensus has convinced the scientific community to deeply investigate marine ecosystems face to climate change, becoming among the top global ocean research priorities. After more than a decade studying OA responses of single species, mostly accelerated for short-time periods in laboratory conditions to projected acidified levels, it is time to progress our knowledge by better projecting ecological impacts of future climate change scenarios.

Recent findings show that some calcifiers do not seem to be affected by OA. Not only were their responses highly species-specific but varied among experiments. These divergent results have clearly shown that our actual knowledge on biological responses to OA and the physiological mechanisms involved are extremely limited and that some assumptions we have used so far might be inaccurate. In addition to these gaps of knowledge, all the data collected so far are single species responses to artificial conditions. Only few studies have scaled-up single species responses to the ecosystem scale. In our study, we aim at deciphering past misconceptions on the effects of OA, and promoting challenging research priorities in the field. This includes: i) to simultaneously test OA with other global environmental alterations, such as warming and euphotication, which will likely exacerbate the organism's sensitivity to OA; ii) to perform experiments in natural conditions, over longer periods, to guarantee at least a complete acclimation of organisms to natural variations. This requires a rapid implementation of in situ experimental systems able to change and to maintain suitable altered conditions; iii) to investigate keystone species/habitats potential abilities to adapt fast enough to environmental changes in order to guarantee vital ecosystem functions in the future. The best way to do that is through the use of sites naturally enriched in CO2 which have successfully been used as natural laboratories to study natural response of ecosystems to OA.

### O-1111-02

#### Bangladesh's coastal vulnerability under climate change

M. Becker (1); F. Papa (2); S. Calmant (1); V. Ballu (3); P. Valty (4); M. Karpytchev (5); L. Testut (6); F. Hossain (7); C. Shum (8); A. Liibusk (8); S. Ouillon (1)

(1) IRD, LEGOS, Toulouse, France; (2) Institut de Recherche pour le Développement, LEGOS and IFCWS, Iisc India, Toulouse, France; (3) CNRS/University of La Rochelle, LIENSs, La Rochelle, France; (4) IGN, Lareg, Paris, France; (5) Université de La Rochelle, Lienss, La Rochelle, France; (6) LEGOS/LIENSs, Toulouse, France; (7) University of Washington, Dept. of civil & environmental engineering, Seattle, United States of America; (8) Ohio State U./School of

Earth Sci., Div. of geodetic science, Columbus, United States of America

In Bangladesh, the Ganges, Brahmaputra, and Megha Rivers come together to form the largest river delta in the world. This low-lying region of the Bay of Bengal is one of the most human-occupied countries in the world and is prone to monsoonal flooding, which is aggravated by an intense annual cyclonic activity. In this context, sea-level rise, along with tectonic, sediment load and groundwater extraction induced land uplift/subsidence, significantly exacerbate the Bangladesh's coastal vulnerability. Here we present the goals and first results of a Belmont Forum/IGFA-funded project, BanD-AID (http://Belmont-SeaLevel.org) that addresses the causes and consequences of coastal vulnerability of Bangladesh. The project's outcome will establish an advanced observation system based on contemporary space geodetic sensors to quantify (1) causes of sea-level rise and land motion and establish their robust vertical datum link, and (2) human interactions that governs coastal vulnerability and resilience in Bangladesh. We present the first results such as the apparent sea level rise at the Bangladesh coast gained by combining space geodetic observations, including satellite altimetry, GRACE and GPS, together with in-situ tidal and river gauges, and different reconstructed sea-level approaches. This unique combination of different satellite techniques and in-situ information offers the possibility to better quantify the major contributions to the relative sea-level rise at the Bangladesh delta, towards addressing its coastal vulnerability and future sustainability.

### O-1111-03

#### Coastal vulnerability to climate change-induced sea-level rise may be increased by land motion and human factors

V. Ballu (1); J. Aucan (2); V. Duvat-Magnan (3); B. Pelletier (4); M. Gravelle (5); C. Shum (6); M. Karpytchev (7); M. Becker (8); F. Hossain (9); P. Simeoni (10); P. Valty (11); S. Calmant (8); Z. Khan (12); T. Kanas (13); L. Testut (14)

(1) CNRS/University of La Rochelle, LIENSs, La Rochelle, France; (2) IRD, Legos, Nouméa, New Caledonia; (3) UMR LIENSs 7266 University of La Rochelle - National Centre for Scientific Research (CNRS), Geography, La Rochelle, France; (4) Grand Observatoire du Pacifique Sud GOPS, Nouméa, New Caledonia; (5) CNRS/Université de La Rochelle, Lienss, La Rochelle, France; (6) Ohio State U./School of Earth Sci., Div. of geodetic science, Columbus, United States of America; (7) Université de La Rochelle, Lienss, La Rochelle, France; (8) IRD, LEGOS, Toulouse, France; (9) University of Washington, Dept. of civil & environmental engineering, Seattle, United States of America; (10) Geo-conute, Port-Vila, Vanuatu; (11) IGN, Lareg, Paris, France; (12) IWM, Dhaka, Bangladesh; (13) Land Survey, Port-Vila, Vanuatu; (14) LEGOS/LIENSs, Toulouse, France

Sea-level rise has been recognized as a major source of coastal vulnerability. Several areas, including low-lying Pacific islands and low lying countries such as Kiribati, Tuvalu, Marshall Islands and Bangladesh have been identified as being highly vulnerable to the effects of sea-level rise. While the ajofajib global source of sea-level rise is climate change, several other local factors can have as strong or stronger an effect than climate-based sea-level rise on coastal vulnerability.

We will present several case studies illustrating situations where increased coastal vulnerability is not solely attributed to climate change. We describe several other factors that can enhance the relative sea-level rise, such as natural factors like tectonic motions, erosion, sediment loading and local sea-level variability, and human factors like poorly designed development. Illustrating these factors using examples from Kiribati, Vanuatu, New Caledonia and Bangladesh, we emphasize that although climate related sea-level rise is a global issue, it can be locally combined with several other factors, modulating its value and impact. Studies of each individual case at the local scale are SAR together with a laboratory for adequate prediction and mitigation in the future.
## Influence of climate changes on mangrove ability to fix and store CO2

C. Marchand (1) ; T. Meziane, (2) ; M. Allenbach (3) ; A. Leopold, (3) ; TT. Nhutrang (4) ; A. Alfaro (5)

(1) Institut de Recherche pour le développement (IRD), Paris, France; (2) MNHN, Paris, France; (3) University of new caledonia, Noumea, New Caledonia; (4) University of new caledonia, Niuatapu, Tuvalu; (5) University of Technology of Auckland, Auckland, New Zealand

Mangroves are forested ecosystems developing in the intertidal zone of tropical and subtropical coastlines. They cover up to 140,000 km² worldwide, and extend from 30°N to 38°S. They are amongst the most productive ecosystems in the world (2). Furthermore, they have been suggested to be enhancers of heterotrophic secondary production and offshore fisheries. In addition, it is well recognized that tropical mangrove ecosystems provide a high abundance of food, shelter, and breeding and nursery habitats for a diverse community of terrestrial, aquatic and aerial organisms, including many endangered species (3). At a larger scale, the high net primary productivity of mangroves and low decomposition rates results in global atmospheric CO₂ sinks in addition. Mangroves are crucial for important ecological and economically supporting a wide variety of ecosystem services (5). For example, mangroves stabilize the shoreline and serve as barriers against erosion. One of the most dramatic examples of the efficiency of this biological system as protection from catastrophic climatic events was demonstrated in 2004, when a large-scale tsunami devastate most coastal areas, but mangrove forest shorelines were significantly less affected. The annual economic value of mangroves, including products and services has been estimated to be US$ 200,000-900,000 ha⁻¹ (7). Mangrove ecosystems have been decreasing dramatically worldwide, mainly due to habitat destruction. Once mangroves cover more than 200,000 km² worldwide (8). However, human population growth and urbanization of coastal areas, expansion of industrial activities, and exploration and exploitation of natural resources have resulted in a current decrease in mangrove area, and the declining rate is equivalent or even higher than that of other threatened ecosystems, such as coral reefs or primary rainforests (9). Mangrove ecosystems also are also threatened by climate change. However, the responses of mangrove ecosystems to climate changes may not well understood (10). Relative sea-level rise may be the greatest threat to mangroves because most mangrove sediment surface elevations are not keeping pace with sea-level rise (11). Additionally, the increased rate of sea-level rise (SLR) and the associated increase in atmospheric CO₂ concentrations may also modify their functioning and distribution. Reduced mangrove area and health will increase the threat to human safety and shoreline development from coastal hazards, such as erosion, cyanobacterial events, and tsunamis (12). Mangrove habitat loss also may reduce coastal water quality, biodiversity, and fish and crustacean breeding and nursery habitats. Such ecological deterioration may have direct and indirect adverse effect on adjacent coastal habitats, and may eliminate a major resource for human communities that rely on mangroves for numerous products and services. Mangrove destruction also has the potential to release large quantities of stored carbon, which can have dramatic global implications (13). A synthesis of the current knowledge will be proposed, and our project of mangrove monitoring in the Indo-pacific area will be presented.

1. Giri et al., 2011. Status and distribution of mangrove forests... Global Ecology and Biogeography 20, 154-159 /2. Bouillon et al., 2008. Mangrove production and carbon sinks... Global Biogeochemical Cycling 22, GB 2013 /3. Nagelkerken et al., 2008. The habitat function of mangroves... Aquat. Bot. 89, 155-185 /4. Donato et al., 2011. Mangroves among the most carbon-rich forests... Nature Geoscience 4, 293-297 /5. Barbour, 2007. Valuing mangrove services... Economic Today 22, 177-229 /6. Walters et al., 2008. Ethnobiology, socioeconomics and management of mangrove forests... Aquat. Bot. 89, 220-236 /7. Wells et al., 2006. Shoreline Protection... UN Environment Programme World Conservation Monitoring Centre, 33 pp. /8. Spalding et al., 1997. World Mangrove Atlas, International Society for Mangrove Ecosystems, Japan /9. Duke, et al., 2007. A world without mangroves? Science 317, 42-43 /10. Gilman et al., 2008. Threats to mangroves from climate change... Aquat. Bot. 89, 237-250 /11. Lovelock, C.E., Ellison, J.C., 2007. Vulnerability

of mangroves... In: Climate Change and the Great Barrier Reef: A Vulnerability Assessment, pp. 237-269 /12. Danielsen et al., 2005. The asian tsunamis... Science 310, 643 /13. Kristensen et al., 2008 Organic carbon dynamics in mangrove ecosystems...Aquat. Bot. 89, 201-219

## Evolution of dengue epidemics in the south pacific in the present and the future

C. Menkes (1) ; M. Mangeas (2) ; M. Teurlai (3) ; V. Cavarero (4) ; M. Daures (5) ; E. Descloux (6) ; N. Degallier (1) ; L. Guillaumot (7) ; JP. Grangeon (5) ; F. Mathieu-Daudé (7) ; M. Lengagne (9) ; A. Mercier (1) ; M. Dupont-Roueyz (8) ; J. S. Hales (10) ; L. Mciver (11) ; J. Benzler (12) ; VM. Cao-Lormeau (13) ; C. Duthiel, (1) IRD, Locean, Noumea, New Caledonia; IRD, Espace-dev., Montpellier, France; (3) IRD, Locean/espace-dev., Noumea, New Caledonia; (4) Métoé-France, Noumea, New Caledonia; (5) DDASS, Noumea, New Caledonia; (6) Territorial Hospital Centre, Noumea, New Caledonia; (7) Institut Pasteur de Nouvelle Calédonie, Noumea, New Caledonia; (8) IRD, Migevec, Noumea, New Caledonia; (9) UPMC, Paris, France; (10) University of Otago, Wellington, New Zealand; (11) National Centre for Epidemiology and Population Health, Australian National University, Canberra, Australia; (12) Robert Koch Institute, Berlin, Germany; (13) Institut Louis Mallard, Papete, French Polynesia

Dengue fever is one of the most important mosquito-borne viral disease, with 390 million people being infected each year and 2.5 billion people living in areas at risk of dengue worldwide. The rapid global spatial spread over the past 40 years is likely to be due to recent socio-economic changes such as urbanization and uncontrolled urbanisation but these factors need to be associated with suitable climatic conditions before dengue fever can establish itself in a given country, for it is transmitted by a number of mosquito species, mainly Aedes aegypti, whose life cycle is influenced by temperature, rainfall and humidity. In the following contribution, we focus on the South Pacific region, a vast, oceanic region where dengue epidemics are recurrent, aiming at disentangling socio-economic factors from climate factors.

We first analyse an original dengue database covering the 1971-2009 period across the South Pacific. In the Pacific region, dengue epidemics occurred every 3 to 6 years, with each epidemic wave caused by the regional circulation of 1 of the 4 dengue virus serotypes, with very limited serotype co-circulation. There are no apparent spatial propagation patterns in the region and countries such as French Polynesia and New Caledonia are the most regularly affected. There is a weak anti-correlation between the major El Niño climate variability and the annual number of countries experiencing an epidemic, suggesting a link between climate and dengue epidemics. However, while the South Pacific has experienced a weak +0.5°C trend in temperature, there is no detectable overall/ regional long-term trend in the evolution of the number of affected countries for the past 40 years. However, local trends exist: New Caledonia is experiencing a positive trend whereas dengue epidemic frequency is decreasing in some smaller islands. We then analyse dengue epidemic profiles per country (endemic, regular epidemics, or sporadic epidemics). We identify variables linked to the different profiles by fitting a statistical model based on variables characterizing the socio-economic situation (e.g. GDP) or climate (e.g. temperature) in each country. These statistical models are able to reproduce the major epidemic profiles. Assuming the socio-economic variables to remain constant over time, we project these models for the next 100 years using models of the IPCC-AR5 under RCP8.5.

Finally, we focus on the case of New Caledonia where very high quality data allows a more quantitative analysis. At present, dengue epidemics are uncontrolled every 6 years. Using spatial statistical modelling, we show that the primary variables explaining the spatial distribution of incidence rates are the mean temperature and a variable highly correlated with people's way of life. Using this model, we show that by the end of the 21st century, with temperature increasing by approximately 3°C as projected by 6 IPCC-AR5 models in New Caledonia, mean incidence rates will be multiplied by two, with areas currently at low risk of dengue being highly exposed in the future. In terms of dengue epidemics recurrences, we also build a temporally dynamic model at weekly time
scales global the detection of the length and beginning of dengue epidemics. One key variable is the number of days where temperature exceeds 32 °C. As this number will increase substantially over the next 100 years in the IPCC-AR5 models, we show that the proportion of dengue epidemic years will rise from 17 % at present to 100 % in the RCP8.5 scenario and 66 % in the RCP4.5 scenario, with the duration of dengue epidemics substantially increasing compared to the present day. Implications for the future of dengue virus circulation in the South Pacific are discussed on the basis of our results

1111-POSTER PRESENTATIONS

P-1111-01

Mass mortality events in atoll lagoons: present environmental control and increased future vulnerability with climate change

S. Andréfou (1); C. Dutheil (1); C. Menkes (2); M. Bador (3); M. Lengaina (4)

(1) IRD, Noumea, New Caledonia; (2) IRD, LOCEAN, Noumea, New Caledonia; (3) CERFACS, Climate Modelling and Global Change team, Toulouse, France; France (4) UPMC, Paris, France

Several geographically closed atolls of the Pacific Ocean have experienced in recent decades mass benthic and pelagic lagoonal life mortalities, that are due to unusual calm weather conditions lasting for several weeks. These events, although poorly known and characterized, pose a major threat for resource sustainability for islanders, and need to be taken into account for long-term resource management. A sample of eleven mortality events on eight atolls from the central South Pacific occurring between 2003 and 2012 were revisited to estimate the environmental threshold related to trigger such events. We investigated thresholds and spatial patterns of sea surface temperature, significant wave height and wind stress satellite data. Then, using these thresholds, spatial maps of present-day potential risk are produced for the central South Pacific region. The highest risk zone lies north of the Tuamotu Archipelago in French Polynesia. To assess future risks in a climate change era, a regional climate model was used to downscale the projected future climate to estimate the potential change in risk due to the end of the 21st century. This process highlights a relative risk increase of up to 60% for the eastern Tuamotu atolls/! However, caution is required given the limited number of case-studies available to train the analysis and identify thresholds. This study suggests that long-term monitoring of the biophysical conditions of the lagoons at risk is needed to properly identify the physical thresholds and better understand the biological processes involved in these rare, but consequential, mass mortality events.

P-1111-02

Mesopelagic heterotrophic N2 fixation related to organic matter composition in the Solomon and Bismarck Seas (Southwest Pacific)

M. Benavides (1); PH. Moisander (2); H. Berthelot (3); T. Dittmar (4); O. Grosso (5); S. Bonnet (6)

(1) Mediterranean Institute of Oceanography, Marseille, France; (2) University of Massachusetts Dartmouth, Biology, Dartmouth, United States of America; (3) Aix Marseille University, Mediterranean Institute of oceanography, Marseille, France; (4) Institute for Chemistry and Biology of the Marine Environment, Research group for marine geochemistry, Oldenburg, Germany; (5) CNRS, Mediterranean institute of oceanography, Marseille, France; (6) IRD, Mediterranean Institute of Oceanography, Noumea, France

The oceans play a key role in absorbing carbon dioxide (CO2) emitted by human activities. This absorbing power depends largely on the activity of downscale, which take up CO2 using nutrients and sunlight. The availability of nutrients is thus essential for maintaining life in the oceans and balancing global CO2 levels. In open ocean areas nitrogen is mainly provided through nitrogen fixation, a process performed by specific microorganisms called diazotrophs. Primary production in the oceans is strongly limited by the availability of fixed nitrogen. In open ocean nutrient-impoverished areas, which make

up ~50% of the global ocean surface, nitrogen is mainly provided through the process of biological atmospheric nitrogen (N2) fixation. N2 fixation is carried out by the so termed diazotrophs, marine microorganisms that may belong to the cyanobacteria, bacteria or archaea. For many years, autotrophic diazotrophs were thought to be the most abundant diazotrophs in the ocean. Autotrophic diazotrophs need light to fix carbon dioxide via photosynthesis, and therefore are constrained to the sunlit layer of the ocean, which is generally less than 100 m deep. Recent investigations have revealed that heterotrophic diazotrophs, which cannot photosynthesize, are present in greater abundance than autotrophic diazotrophs in the world's oceans. Heterotrophic diazotrophs are not constrained by the availability of light and therefore are able to live in the dark ocean, the largest and less studied habitat on Earth. This discovery significantly expands the boundaries where N2 fixation was thought to be possible and theoretically increases the inputs of fixed nitrogen to the ocean, which remain unaccounted for. The diazotrophs inhabiting mesopelagic dark waters are heterotrophic and depend on organic matter for their nutrition. In this habitat, these microorganisms can live in association with oxygen minimum zones or local oxygen deficit microzones like organic particles. However, the relationship of heterotrophic diazotrophic activity and diversity with organic matter is unknown. We investigated N2 fixation along two transects in the Bismarck and Solomon Seas (Southwest Pacific, Transsects 1 and 2 respectively). In Transect 1, transparent exopolymer particles (TEP) where higher and oxygen concentrations lower than in Transect 2. The presence of N- and P-containing dissolved organic matter (DOM) compounds was also higher in Transect 1 than in Transect 2, as revealed by Fourier transform ion cyclotron mass spectrometry. N2 fixation rates (0.09 Nmol L-1 h-1) were higher in Transect 2 than Transect 1, and correlated positively with TEP and negatively with oxygen, reflecting the dependence of mesopelagic heterotrophic diazotroph activity on organic matter. The scores of the multivariate ordination of DOM samples (principal coordinate analysis) were negatively correlated with bacterial abundances and positively correlated with N2 fixation rates. We interpret these results as an active bacterial exploitation of the DOM pool and its use to sustain diazotrophic activity. Phylogenetic analyses of the nifH gene detected y- and β-proteobacteria (Cluster I), Cluster III and Cluster IV. The relative importance of anaerobic Cluster III phylotypes in our clone library (26% of sequences), suggests that N2 fixation was partially supported by diazotrophs with a particle-attached lifestyle. Custom-designed quantitative PCR primer-probe sets were designed for three selected phylotypes. The abundances of a phylotype close to Cluster III ranged from undetectable to 1000 nifH gene copies L-1. Altogether, our results provide new insights into the mysterious ecology of heterotrophic diazotrophs and suggest that in situ organic matter sustains their N2 fixation activity. The input of fixed N2 by these organisms is significant and potentially contributes significantly to nutrient replenishment and primary production in the SW Pacific.

P-1111-03

Autonomous observations with Bio-Argo floats in the Southern Ocean

S. Blain (1); H. Claustre (2); S. Speich (3); J. Uitz (2); A. Poteau (2); G. Obolensky (1); M. Rembauville (1)

(1) Université Pierre et Marie Curie, CNRS, laboratoire Océanographie microbienne, banyuls/mer, France,

(2) CNRS, Université Pierre et Marie Curie, Laboratoire océanographique villefranche, Villefranche sur mer, France;

(3) Ecole normale supérieure, Département de geosciences, Paris, France

The Southern Ocean (SO) is the most remote and the least understood of the world's oceans, although it plays a crucial role in past and present climate state and changes. It is unique in being the only zone unbounded ocean. For this reason, it is the major link by which water properties are exchanged among the other oceans. Moreover, the SO is a major source of natural CO2 due to the upwelling of CO2-rich deep waters and a major sink of anthropogenic CO2 due to the formation of intermediate and bottom waters. The SO also largely contributes to supply nutrients from the deep ocean to the upper water layer everywhere in the world ocean. For all these reasons, the SO plays a critical role in the cure of the Earth's climate. In turn it is very sensitive to climate variability. Given its critical
role, changes in the SO have global ramifications. In fact, such changes are already under way. But at present, the SO remains particularly under-explained. The SO extends over a vast area of the Earth's surface and it is located far away from the other continents and most of the research facilities. Extreme weather conditions and significant sea-ice coverage prevail over most of the year. This results in a scarcity of oceanographic data that limits our ability to understand key climatic-relevant processes and document ongoing changes.

The SCOML (Southern Ocean and Climate) project intends to implement a cutting-edge approach that will qualitatively and quantitatively improve the observation of the SO via pioneering in situ data acquisition with deployment of instrumented profilers and moorings.

Ten new-generation Bio-Argo floats were launched in water off South Africa in the Antarctic Circumpolar Current from December 2014 to January 2015 and they are now entering the Indian sector of the SO. These floats are equipped with sensors that measure salinity, temperature, chlorophyll-a, color dissolved organic matter, backscattering at 700nm, transmission at 650nm, oxygen, nitrate and light attenuation at different wavelengths. They are collecting data in the Sub-Antarctic and Antarctic zones South east of Africa and around the Kerguelen Plateau. We will present the first data gathered during the austral summer and fall 2015. They will provide first insights in the dynamics of the termination of phytoplankton blooms in different environments and contribute to quantify the biological pump of CO2 in the SO. We will also present the plan for the deployment of an instrumented mooring in the region of Kerguelen to be deployed in 2016.

P-1111-04

Carbon production and export are fuelled by dinitrogen fixation and dissolved organic nitrogen in the South-western Pacific Ocean: results from the VAHINE mesocosms experiment

S. Bonnet (1) ; H. Berthelot (2) ; T. Moutin (2) ; S. L'helguen (3) ; K. Leblanc (4) ; S. Hélias (4) ; O. Grosso (4) ; N. Leblond (5) ; B. Charrière (6)

(1) IRD, Mediterranean Institute of Oceanography, Noumea, France; (2) Aix Marseille University, Mediterranean institute of oceanography, Marseille, France; (3) University of Bretagne Occidentale, Lemar, Brest, France; (4) CNRS, Mediterranean institute of oceanography, Marseille, France; (5) CNRS, Lov, Villefranche sur mer, France; (6) CNRS, Centre de formation et de recherche sur les environnements méditerraneens, Perpignan, France

The oligotrophic ocean represents 80 % of the global surface ocean. Its role on CO2 sequestration has long been considered to be low, but this view is currently challenged by new studies highlighting alternative pathways for carbon export to the deep ocean. In these systems, carbon production is limited due to nitrogen (N) scarcity but dinitrogen (N2) fixation and dissolved organic nitrogen (DON) would represent significant nitrogen (N) sources for the ecosystem. Here we deployed in New Caledonia large in situ mesocosms in order to investigate (1) the contribution of N2 fixation and DON use to primary production (PP) and particle export and (2) the fate of the freshly produced particulate organic N (PON) i.e. whether it is preferentially accumulated and recycled in the water column or exported out of the system. The mesocosms were fertilized with phosphate (P) in order to prevent P-limitation and promote N2 fixation. The diatomophic community was dominated by diatoms-diazotrophs associations (DDAs) during the first part of the experiment for 10 days (P1) followed by the unicellular N2-fixing cyanobacteria UCNY-C the 9 last days (P2) of the experiment. N2 fixation rates averaged 9.8±4.0 nM d¹ and 27.8±8.6 nM d¹ during P1 and P2, respectively. NO3- concentrations (<40 nM) in the mesocosms were a negligible source of N indicating that N2 fixation was the main driver of new production all along the experiment. The contribution of N2 fixation to PP was not significantly different during P1 (9.0±3.3 %) and P2 (12.6±6.1 %). However, the e-ratio that quantifies the efficiency of a system to export particulate organic carbon (POExport) compared to PP (e-ratio = POExport/PP) was significantly higher (p<0.05) during P2 (39.7±24.9 %) than during P1 (23.9±20.2 %) indicating that the production sustained by

UCNY-C was more efficient at promoting C export than the production sustained by DDAs. During P1, PON was stable and the total amount of N provided by N2 fixation (0.10±0.02 µM) was not significantly different from the total amount of PON exported (0.10±0.04 µM), suggesting a rapid and probably direct export of the recently fixed N2 by the DDAs. During P2, both PON concentrations and PON export increased in the mesocosms by a factor 1.5-2. Unlike in P1, this PON production was not totally explained by the new N provided by N2 fixation. The use of DON, which concentrations decreased significantly from 5.3±0.5 µM to 4.4±0.5 µM, appeared to be the missing N source. The DON consumption of about 0.9 µM during P2 is even higher than the total amount of new N brought by N2 fixation (about 0.25 µM) during the same period. These results suggest that while DDAs mainly rely on N2 fixation for their N requirements, both N2 fixation and DON can be significant N-sources for carbon production and export. The biological pump in the South Western Caledonia and by extension in the N-limited Ocean where similar events are likely to occur. This study confirms that in the South West Pacific, N2 fixation is a biogeochemically relevant process able to provide sufficient new N to drive new carbon production and export. These results are particularly important in the context of increasing temperatures that will probably increase the diatomization activity in the future ocean.

P-1111-05

The role of dinitrogen fixation on carbon export in the South Pacific: results from the OUTPACE project (Oligotrophy to Ultra-oligotrophy south PACIFIC Experiment)

S. Bonnet (1) ; T. Moutin (2)

(1) IRD, Mediterranean Institute of Oceanography, Noumea, France; (2) Aix Marseille University, Mediterranean institute of oceanography, Marseille, France

The additional CO2 in the atmosphere, mainly resulting from fossil fuel emissions linked with human activities (anthropogenic CO2), is the main cause of global warming. The ocean has acted as a major sink of anthropogenic CO2 preventing a greater accumulation in the atmosphere and therefore a greater increase in the earth temperature. Although the biological pump provides the main explanation for the vertical gradient of carbon in the ocean, it was thought to be in an equilibrium state with an associated near-zero net exchange of CO2 with the atmosphere. Climate alterations are beginning to disrupt the equilibriums expected modification of the biological pump will probably considerably influence oceanic carbon sequestration (and therefore global warming) over a decadal time scale.

The overall goal of the OUTPACE (Oligotrophy to Ultra-oligotrophy PACIFIC Experiment) project is to obtain a better representation of the influence of nitrogen fixation on the biological carbon pump in the South Western Pacific Ocean. The international OUTPACE cruise took place between February 18 and April 2, 2015, involved 30 scientists onboard, and covered around 5 500 km in the South Western Pacific Ocean from the North of New Caledonia to Tahiti.

The very first results are discussed in the context of global climate change and, more particularly, considering the role of the ocean in carbon sequestration through biological processes.

P-1111-06

The 3-dimensional potential vorticity structure and meridional overturning circulation of the Southern Ocean revealed using ARGO floats and data from instrumented elephant seals

C. Chapman (1) ; JB. Salée (2)

(1) CNRS.LOCEAN-IPSL, Paris, France; (2) Sorbonne Universités, LOCEAN-IPSL, Paris, France

The meridional overturning circulation (MOC) of the Southern Ocean is a fundamental component of the climate system. The MOC is a key component of the control over the heat and CO2 budgets of the globe, forming the Earth's
large CO₂ sink and mediating the exchange of heat, salt and chemical constituents southward and between ocean basins. Understanding the MOC is vital for understanding the climate system and predicting its future states.

To date, the vast majority of studies interpret the Southern Ocean MOC through a quasi 2-dimensional framework known as the Transformed Eulerian Mean (TEM). The TEM framework, developed for the study of the large scale atmospheric circulation, generally relies on zonal or streamwise averages. However, the Southern Ocean circulation is not 2-dimensional. Phenomena such as meso-scale turbulence, forced topographic meanders and mixing processes are highly localised due to the interaction between the Southern Ocean currents and large scale bathymetry. These local dynamics effect not only the regional, but the global potential vorticity structure of the Southern Ocean. It has been hypothesised that these local dynamics might have a strong influence on the MOC. We present the results of a systemic program to study the MOC as a 3-dimensional system. Employing hydrographic profiles obtained from ARGO floats, cruises and instrumented elephant seals we develop maps of the 3-dimensional potential vorticity, geostrophic velocity and the associated fluxes due to stationary meanders. Using approximate force balances, we will use these maps to investigate the local overturning in the upper 2000m. Finally, we will discuss the implications for the large scale overturning.

P-1111-07

## The O2C3 Project: Observing Pacific island societies facing climate change. Methodological, epistemological, ethical, and political implications

V. David (1); PY. Lemeur (1); C. Sabinot (2); G. David (3); M. Mangeas (4); E. Rodary (5); V. Naidu (6)

(1) IRD, Département sociétés urm gred, Nouméa, New Caledonia; (2) IRD, Umr 228 "espace pour le développement", Nouméa, New Caledonia; (3) Institut pour le Développement (IRD), UMR 228 ESPACE DEV, Montpellier, France; (4) Institut de recherche pour le développement, Mathematics, espace-dev, Montpellier, France; (5) IRD, Département sociétés urm gred, Montpellier, France; (6) University of the South Pacific, School of governance, development and international affairs, Suva, Fiji

Pacific island societies bear the historical hallmark of vulnerability, mobility and resilience. They have displayed adaptive capacities on the long run as far as livelihood, social institutions and political organization are concerned. The current intensification of global and climate changes could jeopardize these polities as well as pushing them to elaborate innovative solutions to face these dramatic trends. Current research programs carried out by IRD social scientists with colleagues from other institutions or, It has been hypothesised that these local dynamics might have a strong influence on the local systems. The South Pacific Integrated Observatory for the Environment, Terrestrial and Marine Biodiversity in the Social Sciences and Humanities, to enhance cooperation and collaboration initially among scholars based in New Caledonia and Fiji (USP) but with the intention to promote immediate Oceania wide collaboration.

The focus of the O2C3 observatory would be on enRKp's knowledge, norms and practices in an encompassing framework, including various registers of knowledge: local/traditional, administrative, scientific, statistical, legal, professional... This self-evident idea raises serious challenges as far as methods, epistemology, data management, ethics are concerned. Collecting legal texts and scientific articles dealing with the issue does not raise specific difficulty, aside from localizing and accessing sources and making relevant information available to all. Identifying mobility forms linked to climate change (climate and environmental refugees, let alone mining refugees) is

also feasible. When it comes to local knowledge, practices and representations of environmental and climate changes, things become trickier. There is a need for developing an in-depth reflection (1) on pertinent disciplinary and transdisciplinary concepts that could be mobilized in social sciences for collecting and analyzing these data and (2) on the methodological and ethical implications of this type of data production and maintenance.

The O2C3 project seeks to contribute to this effort by bringing together social scientists to cooperate on the human dimensions of climate change. The first step would be to develop a collective framework on the issue of producing, collecting, managing social data on climate change and how to make them available quickly to stakeholders and decision makers. The second step would be to establish an expanding network of social scientists and humanity scholars that will focus on Pacific Island Countries and Territories (PICTs) people's awareness of climate change causes and consequences, stake holder standpoints, and governments' policies and policy implementation on climate change. Third step, it will build and host a shared digital database of information relating to climate change that will be a useful resource for above-mentioned decision makers, academics and other stakeholders.

P-1111-08

## Variability in subtropical-tropical cells drives oxygen levels in the tropical Pacific Ocean

O. Duteil (1); C. Boening (1); A. Oschlies (1)

(1) GEOMAR, Kiel, Germany

Previous studies found a negative trend in oxygen concentrations in tropical regions during the last decades. Employing a biogeochemical circulation model, we highlight the importance of wind driven ocean transport associated with the Subtropical-Tropical Cells (STCs) in setting the oxygen levels in the tropical ocean. The observed and simulated slowdown of the STCs by 30 percent from the 1960s to the 1990s caused a decrease in oxygen transport to the tropics. Transport of phosphate was similarly reduced, decreasing export production and respiration. The effects of physical transport and biological consumption partly compensate, damping oxygen interannual and decadal variability. Our results suggest that the observed residual oxygen trend in the tropical Pacific is mainly driven by changes in oxygen transport. Accordingly, the observed recent strengthening of the STCs leads us to expect a pause in the oxygen decrease or even an increase of tropical Pacific oxygen values in the near future.

P-1111-09

## Impact of the initialization with different ocean reanalyses on forecast bias in seasonal hindcasts

E. Exarchou (1); C. Prodhomme (1); V. Guemas, (1); F. Doblas-Reyes (1)

(1) IC3, Barcelona, Spain

We analyze seasonal hindcasts performed with EC-Earth3 that are initialized from two different ocean reanalysis estimates (ECMWF-ORAS4 and MERCATOR-GLORYS2V1), with the goal to investigate the impact of the different ocean reanalysis on the model bias and the model forecast skill. The seasonal hindcasts are four months long, consist of 10 ensemble members and they are initialized every May and November between 1993 and 2009. We find that the forecast initialized with ORAS4 is globally more skillful than the one initialized with GLORYS, particularly in the tropics. To study how the SST bias development relates with skill, we focus on the Tropical Atlantic, and in particular in two specific regions: the Atlantic3 region (ATL3), and the Angola-Benguela Area (ABA), where most climate models exhibit strong systematic biases. In both sets of hindcasts, a strong warm surface temperature bias develops in less than one month in winter or summer in ABA, and a strong cold surface temperature bias develops in one month in winter in ATL3. The biases in ATL3 in the hindcasts initialized with GLORYS2V1 are circularly strong in 1997, 2001 and 2003, and are caused by subsurface temperature errors in GLORYS. Despite the warm surface temperature
biases in ABA, monthly mean net surface fluxes errors are negative, indicating that errors in SST most likely have an oceanic origin; this is also corroborated by the presence of strong subsurface temperature biases. Errors in the upwelling of the water masses could be in turn related to wind stress errors. We further investigate this possibility by performing additional sensitivity experiments using fixed wind stress over the upwelling regions.

## P-1111-10

### Ant invasions in the light of climate change: forecasting a major threat for island biodiversity and economy

H. Jourdan (1); C. Gomez (2)

(1) IRD-Institut de Recherche pour le Développement, UMR 237 IMBE, Nouméa, New Caledonia; (2) IRD- Institut de Recherche pour le Développement, UMR 237 imbe, Nouméa, New Caledonia

In the last four centuries, spread of exotic species have been steeply rising through human mediated transportation, and have been responsive for major changes to natural ecosystems as well as major consequences and damages to human activities with tremendous associated economic costs. This situation is especially exacerbated in island context, where biological invasions are considered as the main driver of change and threat for both biodiversity and human societies. In the same time, the whole biosphere is experiencing consequences of climate change. There is, now, a wide consensus that climate change will also contribute to exacerbate threats posed by invasive species to ecosystems and human societies. Scientists estimate that this will be especially true for ectochiron organisms, whose current distributions are limited by thermal barriers. But to date, these assumptions have not been widely tested or validated. Among ectochiron organisms, ants are recognised as major invasive organisms, according to their high contribution and dominance in ecosystems, high aggressiveness in context of invasion as well as economic losses related to their spread (decreased of agricultural production, damage to infrastructure, management expenses,...). Then this insect group represents an ideal biological model to test current assumptions, especially in the context of fragile insular ecosystems which are considered as major biodiversity hotspots.

Here we present first results of a study, which aims at providing a better understanding of the patterns and processes behind ant invasions as well as the impacts they have on invaded communities and the projections that one can infer from these for the future as a consequence of global environmental change (under climate change driver).

To better understand the main determinants of the distribution of exotic ant species, we developed species distribution models (SDM) to predict suitable ranges for 20 major invasive ants across Pacific islands. We also explored the evolution of these patterns in the future. We modeled current distributions, based on bioclimatic parameters, soil characteristics and land cover. Future climatic data were sourced from the 5th IPCC assessment report, and it had been calibrated and statistically downscaled using the WorldClim data for 'current' conditions, in order to compare projections. Also, we used ordination analysis to define invasiveness potential and develop spatial projection of life history traits on dynamic invasive fronts, localized on distribution maps. Then, to better fit our predictions, we made a downgrade to New Caledonia biodiversity hotspot, which is already affected by 16 ant species and at risk from the last 4 species. It provides us an invaluable opportunity to validate in the field current occurrences, then field data have been use to recalibrate our prediction of the distribution. More answers are needed regarding future ant species assemblages, ecological determinants of the distribution dynamics of introduced ants: How climate is impacting life history traits that will facilitate invasiveness? How ant species assemblages get structured under the influence of life history traits or biotic interactions?

NB: Our project is involved in a current European Eranet Biodiversa funded project 2013-2016 "(FFII) Forecasting Future Invasions and their Impacts."-

## P-1111-11

### Climate change impacts on marine fisheries: assessing the catchment in Peninsular Malaysia

AHM. Kamal (1); J. Ismail (2); H. Idris (3)

(1) Universiti Putra Malaysia Bintulu Sarawak Campus, Animal Science and Fishery, Bintulu, Sarawak, Malaysia; (2) Universiti Putra Malaysia Bintulu Sarawak Campus, Animal science and fishery, Bintulu, Malaysia; (3) Universiti Putra Malaysia Bintulu Sarawak Campus, Animal science and fishery, Bintulu, Malaysia

Global climate change variations over the past 30 years have produced numerous impacts in the abundance and production performance of marine fish and fisheries worldwide. The consequences in terms of flooding of low-lying estuarine habitats due to over rainfall, fluctuation of temperature, dilution of water parameters, devastation of feeding and breeding habitats - salinity fluctuations and acidification of waters, high salinity in coastal area, changes in the sea water table and breeding triggers have raised serious concerns for the well-being of marine fisheries and their production. This study shows that the overall total catchment of marine fisheries was decreased 38% in 2009 compared to 1998 while considers the fishing gears and vessels number used in Peninsular Malaysia. Registered vessels number was increased up to 92% in 2009 compared to 1998 which eventually increased the total catchment volume of marine fisheries. In 2009, the catching efforts and performance was far low as per vessels compared to 1998. Analysis of climate change variables shows that temperature was decreased as rainfall was increased within the year from 1998 to 2009. However, it is still early to conclude that whether climate change variables could have unpleasant impacts on fish production in the tropical seas like Malaysia. In spite of that it is predicted that the prolong exists of monsoon and increases of rainfall in this area resulting the stresses and sometimes interfering on the habitat, reproductive cycle and their related ecosystems in this coastal marine environment in tropics.

## P-1111-12

### Inter-annual Variability of the Upper Ocean Temperature in the Tropical Western Indian Ocean

M. Manyilizu (1); D. Francois (2); P. Penven (3); C. Reason, (4)

(1) University of Dodoma, College of Informatics and Virtual Education, Dodoma, Tanzania, United Republic of; (2) Commonwealth Scientific and Industrial Research Organisation (CSIRO), Marine and atmospheric research, Wembley, Australia; (3) Institut de Recherche pour le Développement (IRD), Centre ird de bretagne, Bretagne, France; (4) University of Cape Town, Department of oceanography, Cape Town, South Africa

Interannual variability of the upper ocean temperature in the tropical western Indian Ocean has been studied using a regional ocean model. The strongest SST variability occurs in the offshore region lying over high subsurface temperature variations located between 30 and 130 m. Such a region corresponds with strong variations in the thermocline depth. The lowest SST variations occur in the Tanzanian shelf waters and lie over the subsurface waters with the smallest temperature variations in the upper 200 m. Such smallest temperature variations match with weak variations in the thermocline depth. However, the region with the highest variability of the subsurface temperature is more explained by interannual variability related to strong thermocline variations. The thermocline variations can be associated with local Ekman pumping and/or remote influence from the large-scale climate modes. Anomalous local downwelling (upwelling) and downwelling (upwelling) Robby waves generated during ENSO and IOD events lead to anomalies in the thermocline depth and hence in subsurface temperature. The strong variability in the offshore region is related to strong interannual variability in the thermocline associated with ENSO and the IOD.
## THOT (TaHitian Ocean Time series): a new kind of long-lasting deep-sea oceanographic station in the central South Pacific

E. Martinez (1); H. Claustre (2); M. Rodier, (1); A. Poteau (2); A. Mignot (3); M. Taquet (1); C. Ponsonnet (4); K. Maamaatuaiahutapu (5); C. Maes (6)

(1) IRD-Ifrémé-UPF-ILM, Ecosystèmes insulaires océaniens, Tahiti, French Polynesia; (2) CNRS-Université pierre et Marie Curie, Laboratoire océanographique villefranche, Villefranche sur mer, France; (3) Massachusetts Institute of Technology, Cambridge, Massachusetts. United States of America; (4) Direction des Ressources Marines et Minières, Tahiti, French Polynesia; (5) University of French Polynésia, Tahiti, French Polynesia; (6) IRD-CNRS-Ifrémé-UBO, Laboratoire de physique des océans, Plouzane, France

Through various physical, chemical and biological processes as well as their synergetic interactions, oceans play a key role in the modulation of climate system, carbon cycle and biota in marine ecosystems. In the central South Pacific, including the 47% of the French maritime domain of French Polynesia, ocean dynamic plays a key role in the El Niño Southern Oscillation (ENSO). ENSO is the dominant mode of interannual variability in the Pacific with strong effects at global scales. It also modulates the decadal oscillations of the Pacific Ocean and longer-term trends. Furthermore, being part of the South Pacific subtropical gyre, variability of the French Polynesia waters is representative of those in the subtropical gyres of the global ocean. To observe and characterize climate changes in this region, the deployment of long-lasting oceanographic survey stations is necessary to follow the evolution of oceanographic key parameters (e.g., temperature, salinity, oxygen, phytoplankton biomass). However, presently there is no deep-sea monitoring observatory in the central South Pacific.

The objective of the TaHitian Ocean Time-series (THOT) project is to set up a deep-sea oceanographic station to observe and improve the understanding of climate changes in the French Polynesia waters as representative of subtropical gyre and Pacific scales. This project will be part of existing international programs on climate and ocean observations (Bio-ARGO, CLIVAR). It will provide a synergy and complementarity to long-term observations for global ocean

Implementation of a mooring station, such as those already existing, is complex in French Polynesia due to its geographical, scientific, logistical and technological remote context. Thus the originality of THOT is to set up a long-lasting station to observe climate changes based on 1) a regular deployment of physical-biogeochemical profiling floats in the area of interest over the next two/ three years; 2) then to deploy the next generation of biogeochemical profiling floats capable of horizontal displacement to replace in their initial position.

## Diazotrophic impacts on the biogeochemistry of the South Western Tropical Pacific and the implications of rising temperature and CO2

# 1112 - The Arctic Climate system

## ORAL PRESENTATIONS

## The Physical Basis of Arctic Change

C. Lee (1)

(1) University of Washington, Seattle, United States of America

Research suggests that the Arctic responds to climate change earlier, and with greater intensity, than other components of the earth system, making it a useful

C. Menkes (1); C. Dupouy (2); J. Berman-Franck (3); S. Bonnet (2); F. Deboissieu (1); J. Lefèvre (4); M. Rodier, (5); J. Biegela (6)

(1) IRD, LOCEAN, Noumea, New Caledonia; (2) IRD, Mio, Noumea, New Caledonia; (3) Bar Ilan University, Mina & everard goodman faculty of life sciences, Ramat Gan, Israel; (4) IRD, Legos, Noumea, New Caledonia; (5) Institut de Recherche pour le Développement, Umr-241 eio, Papetee, France; (6) IRD, Mio, Marseille, France

The physical, chemical, biological, and biogeochemical characteristics of the south western tropical Pacific Ocean have been studied since the 1980's. The initial studies focused on the equatorial upwelling which crosses the Pacific and annually enriches surface seawater. Primary productivity in this high-nutrient, low-chlorophyll (HNLC) region is limited by the availability of Fe and regulated by intense zooplankton grazing which provide forage for tuna fisheries. In contrast, in the Melanesian Archipelagoes, the upper layer of the tropical ocean (between 15 and 25°S) is characterized by stable thermal stratification and nutrient-depleted (DIN, DIP), oligotrophic water especially in austral summer. Expansive surface blooms in the region experience strong seasonal and El Nino/La Nina cycles. Thus, primary producers include a high abundance of organisms fixing atmospheric dinitrogen (diazotrophs) that inject new-nitrogen into the system, the diazotrophs (including the cyanobacterium Trichodesmium spp., cyanidium-diazotroph associations and unilluminar cyanobacteria, and heterotrophic bacteria). The new production sustained by diazotrophy and the transfer of this "new N" to the planktonic food web critically impacts regional and global carbon and nitrogen cycling. In coastal lagoons, cyanobacteria are a major component of the food web, and run-off from land drainage and pollutions from land may affect the coastal carbon cycle and lagoon equilibrium. Here we will present a comprehensive review of the biogeochemical investigations over the last 30 years and examine the predicted impacts of increasing sea surface temperatures and elevated atmospheric pCO2 (leading to ocean acidification) on the growth, abundance, and contributions of diazotrophs to carbon and nitrogen cycling in this region.

## Indian Ocean warming trends simulated by an OGCM

R. Sivankutty (1); C. Gnanaseelan, (1)

(1) Indian Institute of Tropical Meteorology, Theoretical Studies Division, Pune, Maharashtra, India

Tropical Indian Ocean (TIO) SST shows a steady increasing trend over the last 50 years. Many recent studies suggests that this surface warming has significant influence on large scale summer monsoon circulation features. In this study we investigate he reasons behind the TIO warming using OGCM simulations. The surface heat flux changes alone cannot explain the surface warming pattern in TIO. Significant changes large scale surface circulation in TIO is simulated by the model. The surface circulation change in TIO closely corresponds to surface wind changes and associated geostrophic response in the ocean. We propose an air-sea coupled feedback mechanism to explain the increased warming rate of central and eastern TIO. Results of model sensitivity experiments controlling the surface forcing parameters confirms that, TIO warming pattern is highly modulated by oceanic processes.

barometer for the health of the global environment. Observed changes in the Arctic marine and cryosphere, including increased seasonality, rapid sea ice loss and accelerated melting of the Greenland ice sheet, are consistent with these ideas of 'Arctic amplification'. Such changes can produce substantial environmental and societal stress, with regional implications and potentially profound global impacts. The resulting challenges include accelerated coastal erosion, changing weather patterns and rising sea level. Arctic environmental change can also produce new opportunities, such as expanded resource extraction and shortened shipping routes. Accurate predictions of Arctic environmental change and its global impact are needed to inform the response to these challenges and support planning of future activity.
However, current predictions sometimes differ from observed Arctic change, motivating efforts to advance our understanding of the physical processes.

This presentation will provide an overview of our current understanding of some prominent changes in the Arctic ocean and cryosphere. A complex interplay between the physics of the atmosphere, cryosphere and ocean, with the potential for positive feedbacks (such as that between reduced ice cover, reduced albedo and increased absorption of solar radiation, known as the ice-albedo feedback) govern the observed response to climate change. This motivates efforts to establish integrated, interdisciplinary, international programs to advance understanding and, ultimately, improve predictive ability. Sustained, climate-scale Arctic observing represents a critical component of such efforts, and the state of such observing systems and their underlying technologies will thus be briefly reviewed here.

## K-1112-02

### Assessment of Arctic Feedbacks

#### B. Soden (1)

(1) University of Miami, Miami, FL, United States of America

Radiative feedbacks in the Arctic play a key role in determining the energy and moisture budgets both at the surface and top of atmosphere which, in turn, influences the atmospheric and oceanic circulation. The Arctic has experienced dramatic declines in summer sea ice over the past decade which has triggered a series of interconnected responses in the surface energy budget and the atmospheric feedbacks. The Arctic has become warmer, wetter, and cloudier. All of these changes further modulate the radiative fluxes at the surface. Observations indicate that the most pronounced warming occurs during boreal winter, with an increase in Arctic mean temperature of roughly 1K. This warming is associated with a pronounced sea ice loss in boreal summer which increases the evaporation rates (i.e. moisture flux). The resulting increase in water vapor and cloud cover enhances the downward long wave flux at the surface, contributing to earlier melt onset and the delayed autumn freeze up. This study will summarize the importance of these relationships using multiple observational data sets and compare the observed feedback strengths to those simulated in coupled ocean-atmosphere models.

## K-1112-03

### Biological impacts of recent climate change in the Arctic

#### D. Hik (1)

(1) University of Alberta, Department of Biological Sciences, Edmonton, Alberta, Canada

The ecology of the Arctic is changing in response to shifts in the climate system. Although Arctic species are well adapted to seasonal and diurnal variability in physical conditions, many of the observed climate-driven changes are leading to fundamental shifts in the structure and diversity of biological processes. What happens in both the marine and terrestrial environments has both local and global implications. For example, the tundra is a huge biome extending across 30 degrees latitude. Vegetation changes show a complex pattern at larger scales, but overall there has been a rapid increase in woody vegetation (shrubs, trees), changes in phenology and albedo as a consequence of earlier snowmelt, and changes in foodweb structure and trophic interactions. Freshwater ecosystems are facing similarly large changes, and the ability of rivers, lakes and wetlands to maintain adequate streamflows, water levels and water quality for ecosystem sustainability is poorly understood. In the marine environment, there is already compelling evidence of a shift towards an increasingly pelagic system in the absence of summer sea ice. In both terrestrial and marine ecosystems, extreme events (e.g. winter rain, fire, storm surges) can overturn long-term trends, but there are still insufficient observations to adequately predict the future. I will provide a brief overview of current understanding of how Arctic ecosystems are responding to climate change and variability, and the most important research needs identified during the 3rd International Conference on Arctic Research Planning (ICARP III).

O-1112-01

### The Regional Arctic System Model (RASM) - A Tool to Advance Science and Reduce Prediction Uncertainties of Arctic Climate Change

#### W. Maslowski (1)

(1) Naval Postgraduate School, Oceanography, Monterey, California, United States of America

Some of the largest changes due to climate warming are expected in the Arctic. However, 21st century projections of the magnitude of these changes vary widely in the latest suite of global climate predictions. In addition, several studies point to strong sensitivity of climate projections to multi-parameter space, varying within physically acceptable bounds. Such variations and sensitivities are the source of large uncertainties and limited skill in reconstructions of the past and present Arctic System, and in projections of the future state of this region.

We introduce a new tool for regional climate modelling, the Regional Arctic System Model (RASM), and demonstrate its advanced capability in simulating some critical physical processes and feedbacks which significantly improve model representation of observed seasonal to decadal variability and trends in the sea ice cover.

RASM is a limited-area, fully coupled ice-ocean-atmosphere-land model that uses the Community Earth System Model (CESM) framework. It includes the Weather Research and Forecasting (WRF) model, the LANL Parallel Ocean Program (POP) and Community Ice Model (CICE) and the Variable Infiltration Capacity (VIC) land hydrology model. The ocean and sea ice models used in RASM are regionally configured versions of those used in CESM, while WRF replaces the Community Atmospheric Model (CAM). RASM has recently been upgraded to CICE Version 5.0 (CICE5.0) with (i) the new prognostic salinity thermodynamic model to represent sea ice growth and melt, (ii) a new anisotropic rheology to capture anisotropic sea ice dynamics at the multi-flux scale (of order 2–10km) and (iii) a form drag scheme to more accurately approximate ice-ocean and ice-atmosphere stresses. In addition, a streamflow routing (RVIC) model was recently implemented in RASM to transport the freshwater flux from the land surface to the Arctic Ocean. The model domain is configured at an eddy-permitting resolution of 1/12° (or ~9km) for the ice-ocean and 50 km for the atmosphere-land model components. It covers the entire Northern Hemisphere marine cryosphere, terrestrial drainage to the Arctic Ocean and its major inflow and outflow pathways, with optimal extension into the North Pacific / Atlantic to model the passage of cyclones into the Arctic. All RASM components are coupled at high frequency (i.e. 20-minute intervals) to allow realistic representation of inertial interactions among the model components.

Model results are presented from both fully coupled and a subset of RASM, where the atmospheric and land components are replaced with prescribed realistic atmospheric reanalysis data for 1948–2009. Selected physical processes and resulting feedbacks will be discussed to emphasize the need for high model resolution and fine-tuning of many present parameterizations of subgrid physical processes when changing model spatial resolution. We also investigate sensitivity of simulated sea ice states to scale dependence of model parameters controlling ice dynamics, thermodynamics and coupling with the atmosphere and ocean. Finally, we show that sea ice extent commonly used to evaluate the model skill is not a sufficient model constraint as the modeled sea ice thickness distribution and volume can vary significantly while ice extent remains unchanged.

## O-1112-02

### IPCC AR5: Projections of Arctic Change

K. Riemann-Campe (1) ; R. Gerdes (1) ; M. Karcher (1) ; F. Kauker (1)

(1) Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Sea ice physics, Bremerhaven, Germany

The climate is changing, which is particularly visible in the Arctic sea ice state. To plan the access to shipping routes, resource extraction, etc. several groups with different
interests would like to know the future development of
Arctic sea ice coverage.

Climate scenario simulations with global coupled
climate models, contributed to the coupled model
intercomparison project phase 5 (CMIP5), are used
to exploit possible scenarios for the sea ice distribution
under climate change during the coming decades. Their
results are also discussed in the IPCC assessment report
no. 5 (AR5). More than 30 models take part in the CMIP5
experiments and together they estimate a very large
uncertainty range for Arctic sea ice. CMIP5 models simulate
the global climate change and their individual strengths
differ regionally. Several studies show that if a limited
number of CMIP5 models are chosen with respect to their
regional strengths, the range of uncertainty decreases
considerably for selected variables.

Within the projects ACCESS (Arctic Climate Change, Economics and Society) and ICE-ARC (Ice, Climate, Economics - Arctic Research on Change) we compare satellite sea ice concentration observations with simulated sea ice concentration of 34 CMIP5 models. The skill of the models varies within the region in the Arctic, the time period of the satellite observation used and the satellite data processing. Thus, we analyse two different satellite derived products over individual regions, which have been discussed as potential sites for resource extractions, as well as the whole Arctic for two different time periods. From this, we select the best four CMIP5 models with regard to the misfit between model and observations. Although the models agree on the general future reduction on sea ice area, they differ in the magnitude of the sea ice decrease and thus the timing of when the Arctic becomes 'ice-free'.

The sea ice coverage correlates well with the near surface
air temperature in summer and with the position of warm
Atlantic water during winter. These correlations exist
in the chosen models but with strong differences. For
example, the position of the warm Atlantic water entering
the Arctic via the Fram Strait and the Barents Sea Opening
varies considerably in the four chosen models. Therefore,
one reason for the differences in future sea ice estimates
from different models is the simulated change of the
atmospheric and oceanic northward heat transport into
the Arctic.

Different sea ice projections between climate models can
be understood not only being due to differences of the sea
ice model component, but the model realisation of oceanic

and atmospheric northward heat transport.

1112-POSTER PRESENTATIONS

P-1112-01

Reconstruction of the Greenland ice sheet
surface mass balance over 1900-2014
with the help of the regional climate MAR
model

X. Fettweis (1) ; H. Gallée (2)

(1) University of Liège, Department of geography, Liège, Belgium; (2) Laboratoire de Glaciologie et Géophysique de l'Environnement, Grenoble, France

With the aim of studying the recent Greenland ice sheet
Surface Mass Balance (SMB) rates with respect to the last
century, we have forced the regional climate MAR model
with ERA-Interim (1979-2014), ERA-40 (1958-2001),
NCEP1 (1948-2004), 20CR (1880-2012), and ERA-20C (1900-2010) reanalysis. While all of these forcing products are reanalyses, MAR simulates
significant differences in SMB over the common period. A
temperature correction of +1°C (resp. -1°C) had notably
to be applied to the MAR boundary conditions given that
ERA-20C (resp. 20CR) is ~1° colder (resp. warmer) over
Greenland than ERA-Interim data over 1980-2010.

Discrepancies in simulated SMB is particularly high in
regions where SMB measurements are missing suggesting
that uncertainties in the current SMB reconstruction are
high and observations are still needed before performing
future projections. Comparisons with SMB measurements
(along K-Transact), ice cores and satellite derived melt
texture allows to select the best reanalysis forced data set.

All of these simulations show that i) the period 1961-1990
usually chosen as reference for SMB and ice dynamics
(stable ice sheet) over Greenland is a period when the SMB
was abnormally high in respect to the last 120 years; ii)
SMB has been significantly decreasing after this reference
period. Both ERA-20C and 20CR forced simulations
suggest a precipitation increase over the last century but
only the ERA-20C forced simulation suggests that SMB
during the 1920-1930 warm period over Greenland is
comparable with the SMB of the 2000's.

1113 - Climate Extremes: Patterns, Mechanisms and Impacts

ORAL PRESENTATIONS

O-1113-01

The timing of anthropogenic emergence in
climate extremes

A. King (1) ; M. Donat, (2) ; E. Fischer, (3) ; E. Hawkins (4) ;
L. Alexander (2) ; D. Karoly (5) ; A. Dittus, (1) ; S. Lewis, (6) ;
S. Perkins, (7)

(1) University of Melbourne, School of Earth Sciences, Melbourne, Victoria, Australia; (2) University of New South Wales, Climate change research centre, Sydney, Australia; (3) ETH Zurich, Zurich, Switzerland; (4) University of Reading, Dept. of meteorology, Reading, United Kingdom; (5) University of Melbourne, School of Earth Sciences, University of Melbourne, VIC, Australia; (6) Australian National University, School of earth sciences, Canberra, Australia; (7) University of New South Wales, Climate change research centre, NSW, Sydney, Australia

Many extreme events can be attributed to anthropogenic
climate change whilst others can not. This has motivated
us to study the time of an anthropogenic emergence (TAE)
of six indices representing temperature and precipitation
extremes. We used multiple historical runs and RCP8.5
projections from six CMIP5 models. We define a quasi-
natural variability for each of these indices at gridbox
level and for sub-continental regions and the globe as a
whole. We determine when an anthropogenic emergence
occurs by comparing index distributions across moving
windows with the quasi-natural variability. We also

investigated how TAE compared for mean temperature and
precipitation with extremes. We found earlier emergence
of extreme temperatures in equatorial regions compared
to other parts of the world and some seasonal variability
in TAE. Spatial aggregation reduces variability in mean and
extreme temperature and precipitation leading to earlier
TAE values. Using limited observational datasets, the same
TAE methodology was applied and signs of emergence
found. Finally, using the CMIP5 models, we show the
regions of the world where anthropogenic signals can
already be detected in our temperature and precipitation
indices to aid in the study of attribution of extreme events
to climate change.

O-1113-02

Extreme heat waves with the Heat Wave
Magnitude Index and their occurrence in
the future

A. Dosio (1) ; J. Sillmann (1) ; S. Russo, (1)

(1) European Commission Joint Research Centre, Institute for Environment and Sustainability, Ispra, Italy

Heat waves are defined as prolonged periods of extremely
hot weather and their intensity, duration, and frequencies
are expected to increase in the future under climate
change.

Recently, a new Heat Wave Magnitude Index (HWMI) was
developed that, by taking into account both heat wave
duration and intensity, enables the quantification of
the magnitude of heat waves across different time periods and
regions of the world.

Here we first apply the HWMI to grade the observed heat waves occurred in Europe since 1950: in fact, although the worst event in the last decades occurred in Russia in 2010 (the strongest recorded globally in recent decades exceeding in amplitude and spatial extent the previous hottest European summer in 2003), many other heat waves, documented in literature and in newspapers, occurred in different European regions in the past decades.

Subsequently, we apply the HWMI to the predictions from several regional climate models (RCM) from the Coordinated Regional Climate Downscaling Experiment (CORDEX). RCMs have been used to downscale CMIP5 Global Circulation Models under different Representative Concentration Pathway (RCP), namely RCP4.5 and RCP8.5. We focus on two regions, Africa and Europe, for which a large ensemble of models' results is available.

Results show that, by the end of this century, under the most severe emission scenario, events with magnitude even greater than the one in Russia in the summer of 2010 will become more frequent and are projected to occur as often as every 10 years for regions such as southern Europe and central Africa.

### O-1113-03

#### The Role of Teleconnection Patterns in Wave Climate and Storms Distribution: The SW Spanish and Wales Coasts Examples

R. Nelson Guillermo (1); A. Giorgio (2); P. Michael (3); T. Thomas, (3)

(1) Universidad del Atlántico, Basic Sciences, Barranquilla, Colombia; (2) Cadiz University, Faculty of marine sciences, Cadiz, Spain; (3) University of Wales Trinity Saint David (Swansea), Swansea, United Kingdom

Tele-connection patterns such as the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) are influenced by climate change, as models predict a weakening of the overturning circulation that may affect both regional and global climate, sea level and extreme waves. Occurrence and distribution of storms is important variables in the incidence of coastal erosion, deterioration and/or complete destruction of ecosystems. This work presents the characterization of wave climate and energy, coastal storms and their recurrence intervals, related to several regional cycles in Cadiz (SW Spanish Atlantic coast), Tenby and Swansea (S Wales, UK). At the former site, wave records include 22 years of data covering the period between 1987 and 2012. Storm characterization was carried out using the Power Index and five classes were obtained, from class I (weak events) to V (extreme events). Storm occurrence probability was 96% for class I (i.e. almost one event per year) to 3% for class V. The return period for class V was 25 years and ranged from 6 to 8 years for classes III and IV storms, e.g. significant and severe events. Classes I and II showed a period of recurrence ranging from 1 to 3 years. Approximately 40% of the change in monthly wave data and storminess indices was related to several teleconnection patterns, being the Arctic Oscillation (AO), with 21.45% and the North Atlantic Oscillation (NAO), with 19.65%, the most important drivers of change.

### O-1113-04

#### Timescales of Change: Unraveling East Africa's Climate Paradox

B. Lyon (1); A. Giannini (1); N. Vigaud (1)

(1) IRI, Columbia University, Palisades, NY, United States of America

East Africa is currently facing something of a climate paradox. Over roughly the past 15 years, the region has been experiencing an increased frequency of drought, particularly during the «long rains» season from March-May. In a seeming contradiction, there is a general consensus among climate change projections that the region of East Africa will become wetter as a result of anthropogenic climate change by the end of the current century. One possible explanation of this discrepancy is that the climate models are not properly responding to increasing greenhouse gases and their influence on East African climate: the future climate of East Africa may in fact become drier, not wetter. Another possibility is that

the recent rainfall decline is associated with processes in the climate system operating on shorter time scales than long-term climate change. In this case, the recent rainfall decline may be masking longer-term climate change. A third possibility is that there is an interaction of processes operating on these different time scales.

This paper will review recent and ongoing research that is helping to the recent variations in East African climate, a combination of observations and climate model experiments indicate that the recent rainfall decline in East Africa has been associated with decadal-scale variations of the climate system, specifically in the Pacific Ocean. Evidence is presented that the rainfall decline in East Africa was manifest as an abrupt shift towards drier conditions that occurred in 1998-99 when the Pacific Decadal Oscillation (PDO) shifted from its warm to cold phase. This shift in the PDO was associated with a colling of eastern equatorial Pacific while the western Pacific has remained anomalously warm. Observational evidence indicates that the recent rainfall decline in East Africa was part of a near-global scale shift in seasonal rainfall patterns, with similar shifts observed previously over the past century. Results from climate model experiments, using only observed sea surface temperatures in the tropical Pacific as forcing, indicate the models are able to reproduce the recent drying in East Africa and the associated shift in global precipitation patterns. However, observations also indicate that the western Pacific warm pool region has continued to warm over the past several decades, an increase which almost certainly contains an anthropogenic component. Current work is investigating whether this combination of «natural» decadal variations and anthropogenic change, particularly in sea surface temperatures in the Pacific warm pool region, led to an exacerbation of recent East African droughts (we note that the devastating drought in 2010-11 was likely the most severe of the past 50 years). Understanding the physical processes associated with climate model projected increases in East African rainfall and how realistic they are in light of what is known about the behavior of the current climate system remains a critical next step in fully unraveling the East African climate paradox.

### O-1113-05

#### Physical insights on future European summer heat waves and record-breaking temperatures

M. Bador (1); L. Terray (1); J. Boé (1)

(1) CERFACS/CNRS, Sciences de l'univers au cerfacs, ura1875, Toulouse, France

Recent summer heat waves had strong socio-economic impacts in different parts of Europe. This highlights the need for improved understanding of key processes and feedbacks. We focus on the detection of an anthropogenic signal on record-breaking summer temperature using historical and 21st century simulations from a set of CMIP5 climate models. Results show that simulated and observed record evolutions follow the stationary climate theoretical record rate until the 1980s. They then diverge from the expected value, with an increase of the number of warm records and a decrease of the cold ones. These changes are shown to accentuate over the 21st century. The influence of internal variability based on control simulations is used to estimate an anthropogenic signal emergence time around 2030.

We then focus on a set of case studies of future heat waves. We analyze a high spatial resolution simulation (from 5° up to 50°) of the regional atmospheric model driven by the CNRM-CM5 model. Based on warm spell duration indices, we select a few intense events that occur in the second part of the 21st century. Heat waves are generally associated with quasi-stationary anticyclonic circulation anomalies that produce clear skies and warm air advection. They are often associated to anomalously dry land surface conditions. For each case study, we perform ALADIN sensitivity experiments by perturbing either the prescribed large-scale circulation and/or the initial soil moisture content. We then infer the dominant mechanisms and the feedbacks operating to amplify or mitigate the heat waves. We also perform a worst-case scenario where we try to generate an extreme heat wave in order to assess the associated temperature rise and its possible saturation due to negative feedback.
## Global future changes of precipitation extremes

A. Toreti (1); P. Naveau, (2); M. Zampieri, (3); A. Schindler, (4); E. Scoccimarro, (5); E. Xoplaki (6); HA. Dijkstra, (7); S. Gualdi, (3); J. Luterbacher (8)

(1) European Commission, Joint Research Centre, Ispra, Italy; (2) Laboratoire des Sciences du Climat et de l'Environnement, IPLS- CNRS, Gif-sur-Yvette, France; (3) Centro Euro-Mediterraneo sui Cambiamenti Climatici, Lecce, Italy; (4) Federal Office of Meteorology and Climatology, MeteoSwiss, Zurich, Switzerland; (5) Centro Euro-Mediterraneo sui Cambiamenti Climatici, Lecce, Italy; (6) Justus-Liebig-University Giessen, Geography: Climatology, Climate Dynamics and Climate Change, Giessen, Germany; (7) Utrecht University, Department of physics and astronomy, Utrecht, Netherlands

Precipitation extremes have a strong impact on ecosystems and societies especially in exposed and vulnerable areas. In a climate change context, where exposure and vulnerability are also expected to change, it is essential to achieve a better understanding and an improved characterisation of these events. By analysing the latest global climate model simulations from the Coupled Model Intercomparison Project Phase 5 and by using an innovative statistical approach, seasonal changes in daily precipitation extremes under the high emission (RCP8.5) and the mid-range mitigation emission (RCP4.5) scenarios are investigated. Two future time periods (2020-2059, 2060-2099) are compared with the historical time period 1966-2005 and the results presented in terms of very high risk events. Furthermore, global models are evaluated with precipitation extremes by using the available high-resolution observations during the selected time period of the historical run. At the European scale, complex changes in the tail behaviour are also assessed. Results show that in the historical period a reliable characterisation of daily extreme precipitation cannot be achieved for large areas of the world, where an estimation of the return levels cannot be obtained. This is the case, for instance, during boreal winter for a belt elongated over the subtropics and in the main tropics of the Northern Hemisphere and the oceanic areas west of the three continents of the Southern Hemisphere. In the Euro-Mediterranean area, northern Eurasia, and North America, the simulations show lower intermodel variability and higher correlation with the observations in boreal winter. Conversely, for Australia, southern Asia, and the Middle East, all seasons are characterised by larger intermodel variability and lower correlation with the observations. Concerning the future projections, the main findings point to an intensification (more pronounced at the end of the century under the high-emission scenario RCP8.5) of precipitation extremes almost everywhere in the world and in all seasons. However, a lack of reliability and consistency affects the subtropics/tropics. The zonal means of the identified changes clearly show more pronounced increases over the high latitudes of both hemispheres in all seasons, with the exception of the Northern Hemisphere in the mid-century boreal summer, associated with larger intermodel variability. Over the Southern Hemisphere, a sharp decrease in the estimated positive changes from the high to the middle latitudes is evident in all seasons followed by (with the exception of the austral winter) a strong increase towards the low latitudes. Stronger hemispheric differences are also estimated over the high latitudes for RCP8.5 at the second half of the century that are most prominent in summer and autumn. At the regional level, models show a better agreement the projected increase of return levels over land, although large variability affects the estimated seasonal changes over specific areas (e.g., eastern Asia in summer).

## Weakened Flow, Persistent Circulation and Prolonged Heat Waves in Boreal Summer

D. Coumou (1); J. Lehmann, (1); K. Kornhuber, (1); V. Petoukhov, (1)

(1) Potsdam Institute for Climate Impact Research, Potsdam, Germany

Changes in atmospheric circulation can strongly alter the frequency and/or magnitude of high-impact extreme weather events. The Northern Hemisphere mid-latitudes

have seen significant changes in the large-scale summer circulation over the last decades and this might have contributed to more prolonged heat waves (1-3). The zonal mean zonal wind (or "jet") has weakened by about 5% over 1979-2014, likely driven by the much more rapid warming in the Arctic as compared to the rest of the Hemisphere. In conjunction with the summer jet, the kinetic energy associated with transient synoptic-scale weather systems (the Eddy Kinetic Energy, or EKE) has seen a significant weakening as well. The observed decline in EKE is more pronounced in relative terms than that of the jet (by about 10% over 1979-2014), which is consistent with theoretical arguments and climate model simulations. Transient eddies are both forced by the jet via vertical shear but can also accelerate it via the eddy-driven jet (4, 5). The observed summertime weakening of both jet and EKE is also a robust signal in future projections of CMIP5 climate models (5, 6). At the same time, for some wave numbers, we have seen an increased occurrence-frequency of high-amplitude quasi-stationary waves during recent boreal summers. We argue that this increase in frequency is associated with a recent cluster of resonance events which can create such high-amplitude waves.

The reduction in amplitude of fast-moving transient waves (as captured by EKE) and the more-frequent occurrence of high-amplitude quasi-stationary waves both favor more persistent weather conditions. It has been demonstrated that high-amplitude quasi-stationary waves in the atmosphere are statistically associated with extreme weather at the surface (7, 8). Especially regions at the western boundary of the continents show the strongest association between surface extremes and high-amplitude upper-level waves. In contrast, strong transient wave activity, i.e. large EKE, is linked to moderate surface temperatures and vice versa (3). Over most continental regions affected by storm tracks, there is a significant negative correlation between monthly EKE and surface temperature. Thus, the hottest summers are associated with extremely low EKE, while mild summers are associated with more pronounced EKE. Again the western boundaries of the continents are especially sensitive since these regions are most directly influenced by the storm tracks.

In conclusion, boreal summer circulation has seen pronounced changes over the last decades, trends which seem to have amplified since the onset of rapid Arctic Amplification around 2000. Especially the reduction in EKE, but also in zonal mean flow, have created conditions favorable for the buildup of heat and drought over the continents. Moreover, a cluster of resonance events is observed since 2000, which has increased the occurrence-frequency of a high-amplitude quasi-stationary waves with wavenumbers close to 7. Thus, this generally implies a weakening of transient synoptic eddy activity and more-frequent states of quasi-stationary flow. These observed changes in large-scale flow point towards more persistent flow patterns and therefore more extreme surface weather. This is also consistent with the pronounced increase in heat extremes in Europe and other mid-latitude regions (9, 10).

J. E. Overland, J. A. Francis, E. Hanna, M. Wang, Geophys. Res. Lett. 39, L19804 (2012).

2. J. A. Francis, S. J. Vavrus, Environ. Res. Lett. 10 (2015), doi:10.1088/1748-9326/10/1/014005.

3. D. Coumou, J. Lehmann, J. Beckmann, Science (80-). J. (accepted) (2015).

4. T. Woollings, M. Blackburn, J. Clim. 25, 886-902 (2012).

5. J. Lehmann, D. Coumou, K. Frieler, A. V. Eliseev, A. Levermann, Environ. Sci. Lett. 9, 084002 (2014).

6. P. A. O'Gorman, Proc. Natl. Acad. Sci. USA 107, 19176-19180 (2010).

7. J. A. Screen, I. Simmonds, Nat. Clim. Chang. 4, 704-709 (2014).

8. D. Coumou, V. Petoukhov, S. Rahmstorf, S. Petri, H. J. Schellhuber, Proc. Natl. Acad. Sci. U. S. A. 111, 12331-12336 (2014).

9. S. Russo et al., J. Geophys. Res. Atmos., n/a/n-a (2014).

10. N. Christidis, G. S. Jones, P. a. Stott, Nat. Clim. Chang. 3-7 (2014).

## Climate Model Simulation of Present and Future Extreme Events in Latin America and the Caribbean: What Spatial Resolution is Required?

R. Oglesby (1); C. Rowe, (2); R. Mawalagedara, (3)

(1) University of Nebraska, Lincoln, Earth and atmospheric
sciences and daugherty water for food institute, Lincoln NE, United States of America; (2) University of Nebraska, Lincoln, Earth and atmospheric sciences, Lincoln NE, United States of America; (3) University of Nebraska, Lincoln, Earth and atmospheric sciences and daugherty water for food institute, Lincoln, United States of America

Latin America and the Caribbean are regions presently at a grave risk to a variety of extreme climate events. These include flooding rains, damaging winds, drought, heat waves, and in high elevation mountainous regions, excessive snowfalls. The causes of these events are numerous. For example, flooding rains and damaging winds are often associated with tropical cyclones, but also can occur, either separately or in tandem, due to smaller, more localized storms. Similarly, heat waves and droughts can be large scale or localized, and frequently occur together (as excessive drying can lead to enhanced heating, while enhanced heating in turn promotes additional drying). Even in the tropics, extreme snow and ice events can have severe consequences due to avalanches, and also on water resources. Understanding and modeling the climate controls behind these extreme events requires consideration of a range of time and space scales. A common strategy is to use a global climate model (GCM) to simulate the large-scale (~100 km) daily, atmospheric, and regional-scale extreme heating on extreme events. A limited area, high resolution regional climate model (RCM) is then employed to dynamically downscale the results, so as to better incorporate the influence of topography and, secondarily, the nature of the land cover. But what resolution is required to provide the necessary results, i.e., minimize biases due to improper resolution? In conjunction with our partners from participating Latin American and Caribbean nations we have made an extensive series of experiments with the region-wide and for individual countries, using the WRF regional climate model to downscale output from a variety of GCMs, as well as Reanalyses (as a proxy for observations). The simulations driven by the Reanalyses are used for robust model verification against actual weather station observations. The simulations driven by GCMs are designed to provide projections of future climate, including importantly how the nature and number of extreme events may change through coming decades. Our results suggest that for proper simulation of both mean climate, and importantly extreme events, a spatial resolution of 4 km is required in regions of complex mountainous topography. A somewhat coarser resolution of 12 km is adequate in regions without much topographic relief, and where differing land covers account for most of the spatial heterogeneity.

## O-1113-09

### Should we expect more extreme rainfall from Atlantic tropical cyclones as a response to global warming?

F. Chauvin (1); H. Douville (1)

(1) Météo-France, CNRM-GAME, Toulouse, France

Daily precipitation extremes increase in intensity over many regions of the globe in simulations of a warming climate, including the tropics where observational constraints suggest that this sensitivity could be higher than expectations. The relationship (e.g. O'Gorman 2012). Here, the focus is on heavy precipitation related to Atlantic tropical cyclones (TCs). The objective is to investigate whether the sensitivity to global warming of TC rainfall is mainly controlled by the atmospheric water holding capacity, following the CC relationship, or could be even higher due to a dynamical cyclone amplification associated with atmospheric arcing release of latent heat in the atmosphere. This amplification may lead to rates of change reaching twice the CC rate (Trenberth 2007). Our investigation is based on TRMM satellite precipitation observations and atmospheric ERA-Interim reanalysis in association with the IBTracs observed TC dataset on the one hand, and on coupled ocean-atmosphere simulations performed with a stretched version of the CNRM-CM5 global climate model on the other hand. For the CNRM-CM5 simulation, aerodynamic TC tracking has been performed. A water budget analysis has been conducted along the cyclone tracks for both observation and model. It was found that moisture convergence is the dominant contribution to TC rainfall, as expected from previous case studies. Results also show that our climate model captures quite well the water budget derived from ERA-Interim, although the latter shows a systematic underestimation

of TC rainfall, as compared with TRMM, possibly due to an underestimation of TC winds. Moreover, the analysis of our climate scenario suggests that the increase of spatially aggregated TC mean rainfall follows the CC relationship, while super CC rates are only reached in the very inner core of the TCs.

## O-1113-10

### Temperature and precipitation extreme compound events in Southeastern South America and the associated atmospheric circulation

M. Rusticucci (1); B. Tencer (1); ML. Bettolli (2)

(1) School of Earth and Ocean Sciences, University of Victoria, Victoria, Canada; (2) University of Buenos Aires, Atmosphere and ocean sciences, Buenos Aires, Argentina

Compound events consist of the simultaneous or successive occurrence of two or more extreme events, the combination of extreme events with conditions that amplify the impact of the events, or the combination of events that are not individually extreme but can lead to extreme impacts when occurring together (the CLARIS LPB project). Four different extreme temperature events were defined: warm nights (days) correspond to days with minimum (maximum) temperature exceeding the 90th percentile of the daily distribution; cold nights (days) are days with minimum (maximum) temperature below the 10th percentile. Heavy precipitation events are events with daily rainfall above the 75th percentile of the empirical distribution of rainy days. A compound event is defined when one of the above temperature extremes occurs simultaneously with, preceded or followed by a heavy precipitation event.

The study is based on a comprehensive dataset of daily precipitation and daily minimum and maximum temperature observed at meteorological stations of the region and compiled during the CLARIS LPB project. Four different extreme temperature events were defined: warm nights (days) correspond to days with minimum (maximum) temperature exceeding the 90th percentile of the daily distribution; cold nights (days) are days with minimum (maximum) temperature below the 10th percentile. Heavy precipitation events are events with daily rainfall above the 75th percentile of the empirical distribution of rainy days. A compound event is defined when one of the above temperature extremes occurs simultaneously with, preceded or followed by a heavy precipitation event.

The existence of a significant statistical relation between these extremes could help to better characterize the uncertainties associated with projections of extreme precipitation events for a future warmer climate. Results show that the probability of occurrence of an intense precipitation increases during or after a warm night, but decreases during a cold night, compared to the expected likelihood of occurrence of this type of events in the absence of a relation between temperature and precipitation extremes. Warm days are usually associated to the occurrence of heavy precipitation events on the same day or the day before, but they rarely occur afterwards. On the contrary, cold days happen more often after an intense rain.

In order to characterize the atmospheric circulation during the occurrence of a compound event, we use a synoptic classification developed by Barrucand et al (2014) and based on daily mean fields of geopotential height at 500hPa from the NCEP2 reanalysis. The associated circulation during a compound event of warm nights or warm days and heavy precipitation shows a trough in the Pacific Ocean and a cold front over the continent that lead to warm and wet air advected to the east of the region of study. Cold days and heavy precipitation events in the southwestern part of the domain of study are usually characterised by a positive anomaly of geopotential height at the southern part of the continent associated with an eastern anomaly over the region.

## O-1113-POSTER PRESENTATIONS

### P-1113-01

### Capability of CORDEX RCMs in simulating extreme rainfall events over South Africa

S. Abba Omar (1); A. Babatunde (2)

(1) University of Cape Town, Environmental and Geographical Science, Cape Town, South Africa; (2) Climate Research Analysis Group (CSAG), Department of environmental and geographical science, university of cape town, Cape Town,
In South Africa, extreme rainfall events often lead to widespread destruction, damage infrastructure, and displace communities, strain water management and even destroy lives. Past studies have shown that reliable predictions of extreme rainfall events from regional climate models (RCMs) could help reduce the impact of these events. This present study evaluates the ability of new RCMs in simulating extreme rainfall events from South Africa, focusing on the Western Cape (WC) and east coast region (EC). This study defines an extreme rainfall over a location as rainfall that is equal or above the 95th percentile of the rainfall distribution at that location, and defines widespread extreme rainfall events (WEREs) over an area as events during which more than 50% of the grid-points in the area experience extreme rainfall. The 95th percentile threshold values were calculated over 11 years (1989-2008) of South Africa's daily rainfall data from nine RCMs which participated in the Coordinated Regional Climate Downscaling Experiment (CORDEX). The simulations were compared to two observation datasets (TRMM and GPCP), and to ERAINT rainfall data to understand whether these RCMs improve on the results from ERAINT. A self organizing map (SOM) was used to characterize WEREs identified in all the datasets into archetypal groups, and ERAINT data were used to describe the underlying circulation patterns for each archetypal rainfall pattern. The number of WEREs mapped to each archetypal pattern for each dataset allows us to get an idea of whether certain RCMs are more likely to simulate certain rainfall patterns.

The results show that RCA35, REMO and WRF seem to be the best at simulating the 95th percentile threshold values over the whole of South Africa. However, it was found that the CCLM seems to do the best over the WC and PRECIS does the best over the EC. Downscaling ERAINT with CCLM produces fewer WEREs, whereas downscaling ERAINT with PRECIS produces a higher number of WEREs simulated over both areas (WC an EC). The SOMs identifies four major patterns of WERE over areas. The first pattern (TRW) links WERE in WC or EC with tropical activities, producing a tropical temperate through that is truncated at the coast. The second pattern links WERE in WC or EC with mid-latitude rainfall activities(MLW). The third pattern produces an isolated WERE over each area (ISW). The fourth pattern, which is unique to WC, links WEREs in WC with rainfall activities over the Azulhas current. The fifth pattern, which is unique to EC, links WEREs in EC with both tropical and mid-latitude rainfall activities, hence producing TTTS. PRECIS has the tendency to overestimate the frequency of TRW WEREs over both the EC and WC whereas, WRF only shows this tendency over the EC. AREGE simulates more WEREs associated with ISW over the EC region and over the WC WRF and CRCMS underestimate the frequencies of these events. Over the EC the frequency of WEREs associated with mid-latitude rainfall activity seems to be simulated reasonably well by the RCMs whereas over the WC most of the RCMs overestimate the frequency of these types of WEREs.

## P-1113-02

# The potential risk of climate change and extreme climatic events on coastal cities of Nigeria

### S. Ayanlade (1)

(1) Obafemi Awolowo University, Ile-Ife, Nigeria, Dept. of Geography, Ile-Ife, Osun, France

This study examines the potential risk of climate change and extreme climatic events on coastal cities of Nigeria. The study applied satellites data, Remote sensing and Geographical Information System (GIS) methodologies to assess the environmental and societal implications and the risk of climatic events such as flooding, coastal erosion and seas surface rise on coastal cities of Nigeria. The risk of climate variability and extreme weather events cannot be overemphasized on urban settlements that occupy millions of people in Nigeria. It is obvious from the report of Nigerian National Population Commission (NPC, 2006) that a large percentage of Nigeria's urban population lives in coastal cities. Previous studies have reported that Climate change has been affecting and will continue to affect almost, if not all, the sectors of the urban economy including the most sensitive ones such as water and health sectors. Such impacts and the risk of climatic event are now obvious in many coastal cities of Nigeria. The impacts of climate change and urban risk may be felt also by a

wide spectrum of socio-economic variables like human health, transport, energy, industry and other service sectors in the coastal cities. Increases in population growth rates in the coastal cities of Nigeria, combined with a likelihood of a 1m sea-level rise, could create high risk on tourism-oriented economies, ecology, and other societal implications. Though, the report of IPCC, (2007) has shown that there are some uncertainties about the nature and magnitude of risk and vulnerability to climatic changes, it is necessary to make some assumptions about risk of changes in climate in order to assess potential such risk on coastal urban settlements of Nigeria. Thus, the general objectives of this study has been to assess the spatiotemporal risk of climatic event; map out a composite of scenarios for climate change impacts; to examine the risk of climatic extreme events on coastal cities of Nigeria; and their implications on physical, economic and social environments. This study holds the benefit for better understanding of a need to have a coastal zone management plan to address the possible coastal cities risk indicated in this study.

## P-1113-03

# The Climate Expectancy: a resolute parametrical approach to redefine the climate

### V. Cailliez (1)

(1) Chambre d'Agriculture de la Creuse, GUERET, France

1) The 30-year average, a largely outdated concept:

Since the climatic break (or powerful acceleration) that happened throughout the world in the late 70s, temperatures are following a steep slope. Considering the whole set of GCM simulations (see IPCC AR5), this trend is not going to slow down, to speak gently. So, we can no longer ignore that the mathematical operation of averaging applies not only on values but also on time, when used on a chronological series.

If we don't renew the definition of climate normality, we will be using the 30-year average of 1981-2010 (i.e. the 1996 expectancy) until 2021, when the 30-year average of 1991-2020 is to be calculated and released. What was tolerable in times of slow and weak fluctuations is becoming unacceptable in a situation where a strong trend is at work (from +0.3°C to +0.5°C per decade in France since the climatic break, for instance).

The link with climate extremes is obvious. An extreme is qualified by its distance to normality. If we define the normality better, we define better what is away from it.

2) Redefining the climate:

The World Meteorological Organization (WMO) classical definition of the climate can be written : observation time series = 30-year average + anomaly time series

The proposition is to refine the 3 terms of the equation by an homogenization of the observed meteorological data, followed by a separation between the random part of the series (replacing the anomaly) and the organized part which is, in fact, the climate expectancy. The underlying idea is to consider that a 'real' anomaly in a time series should be what is totally unexpected, and so, what is part of a random series.

3) Organizational analysis:

The purpose is the separation of the long-term organizations (trend, cycles...) from the short-term ones (persistence...). Considering the long-term organizations, we can write:

$$ \text{Par}(t) = (a^t+b)+\text{Amp1}\sin(2\text{IT}+\text{P1})+\text{Phas1})+\text{Amp2}\sin(\dots)+\dots+\text{ParWLO}(t) $$

where Par(t) is the homogenized series and WLO means Without LongTerm Organization.

The short-term organization is treated in an autoregressive process:

$$ \text{ParWLO}(t) = \text{A1}\text{ParWLO}(t-1)+\dots+\text{Akmax}\text{ParWLO}(t-\text{kmax})+\text{ParWSTO}(t) $$

where Ai are the auto-regression coefficients and kmax is the (maximum) horizon of significant persistence. WSTO means Without long term and ShortTerm Organization.
We can now easily deduce the expression of the climate expectancy ClimPar(t) :

$$ \text{ClimPar}(t) = \text{Par}(t) - \text{ParWSTO}(t) $$

On this expression, it is easy to figure out that we can have a different value of the climate expectancy on each observed data till the last one. The compatibility with the classical WMO definition is achieved simply by centering ParWSTO(t).

The randomness of the ParWSTO(t) series can be verified with multiple statistical tests like the runs tests. It happens that the separation between organized and random parts is excellent. We experienced this with 30-year to 60-year long daily datas of maximum and minimum temperatures, located in the central region of France called Limousin.

Because the ParWSTO(t) series is a random series (or very close to), it can be regenerated by a random number generator. The shape of the random distribution is adjusted dynamically and parametrically to the observed one by analysing the organization of the variance, skewness and kurtosis of ParWSTO(t).

The upgrade of the determination of climate extremes is the result of the whole process which can be summarized as a separation between organized and random variability.

4) Biding farewell to the 30-year average ...

On one side, the 30-year average is an easily explained notion, which needs only simple calculations and is universal. To abandon it will be indeed a difficult human and social process. On the other side the climate expectancy is a quite open concept, delicate to understand at first sight and that can lead to long and uneasy calculations. However its integration into the toolbox of climatologists has to be started soon because of the strength and the inertia of the global warming phenomenon. Its usability at very different scales of time (from hourly to centennial datas at the least) should facilitate a rapid consensus.

## P-1113-04

### Climate change and extreme weather events in Mediterranean Sea: studies with WRF atmospheric model

G. Emmanouil (1) ; M. Vlachogianni (1) ; A. Sfetsos (1)

(1) Demokritos, Athens, Greece

Extreme weather events are becoming more frequent the last years. This fact along with its relation to the possible climate change, are two major issues of scientific study. In this work, WRF-ARW atmospheric model is used to simulate extreme weather conditions in Mediterranean Sea, focusing in the Greek peninsula. Sensitivity tests with different model configurations will be presented, as well as evaluation of the results against in-situ observations. The results show good agreement with observations and prove to be a very useful tool for studying, forecasting and trying to limit down the consequences of such events.

## P-1113-05

### Extreme Rainfall Events in Asia: Projected Changes and Uncertainties

N. Frechet (1) ; A. Duchez (2) ; CH. Wu (1) ; HH. Hsu (1) ; CA. Chen (1) ; A. Forryan (2) ; B. Sinha (2) ; JJM. Hirschi (2) ; AL. New (2)

(1) Academia Sinica, RCEC Research Center for Environmental Change, Taipei, Taiwan; (2) National Oceanography Center (NOC), Southampton, United Kingdom

Extreme precipitation (and drought) are one of the main concern for society and environment, because they can lead to severe flood (and lack of water supply). In warmer environment, atmospheric moisture is expected to increase, and could thus create more favorable conditions to trigger extreme rainfall. However, the change in dynamics can also play a major role in the change of distribution of precipitation. The modification of the land-sea thermal gradient, the vertical structure of the atmosphere, or the latent heat released by the precipitation, can all impact the large scale circulation, and thus the rainfall distribution.

In this study, focussed on the East Asia region, we analyzed

the results from two high resolution models (HiRAM-C192 and HadGEM3-GC2), and from the CMIP5 ensemble, to investigate the projected change in extreme rainfall events (either extreme precipitation or long drought). The role of the SST is also investigate. HadGEM3-GC2 is fully coupled with ORCA025, while HiRAM-C192 is forced by prescribed SST. The SST forcing for this model is determined by a cluster analysis from the CMIP5 projection. Three main patterns of SST are used providing three different projections for this model. We also emphasize the correlation with the dynamics to explain the interannual variability of the extremes events.

In both CMIP5 ensemble and high resolution models the signal of extreme precipitation strongly increase during the summer. On the other hand, the signal on the drought spell is not clear. HadGEM3-GC2 show a decrease during winter of East Asia, while the three HiRAM runs show an increase during this same season. It could be due to a difference of sea-land contrast. The East Asia 200 hPa jet intensity impacts significantly the variability of extremes precipitation, while the winter 850hPa winds show a strong correlation with the drought over East Asia. The results on CMIP5 ensemble also show a significant impact of the change in vertical motion (with a tendency to slow down), that could act as a counterbalance to increase of atmospheric moisture. But large uncertainties remain between different models, and impact strongly the confidence on the extreme projection.

## P-1113-06

### Climate change impacts on social well-being of fishers' communities in the Bangladesh Sundarban

MM. Islam (1)

(1) Sylhet Agricultural University, Department of Coastal and Marine Fisheries, Sylhet, Bangladesh

Social well-being concept has garnered much interest in recent years as a multi-dimensional, holistic approach to understand and measure progress and problems. Though the concept of social well-being has operationalized across different disciplines, there are very few studies using this concept to show how climate change is affecting well-being of fishing communities. To fill this knowledge gap, the study used social well-being approach to study the impacts of climate change on the livelihoods of mangrove fishers' communities in the Bangladesh Sundarban. Qualitative data collection tools were employed; a semi-structured questionnaire was used to collect the empirical data from four fishing communities. Given that, in recent past two consecutive cyclones - Sidr (hit Bangladesh coast on 15th November, 2007), and Aila (struck Bangladesh coast 25th May, 2009) affected a major part of the Sundarbans mangrove ecosystem with great devastation. In addition, the region faces other environmental degradations such as saline water intrusion, occasional droughts as well as degraded resources base of the forest. Thus, ongoing environmental changes in the Sundarbans and its effects on the communities provide a suitable setting to study the impacts on climate changes on the well-being of the residing population. Following the Web framework of wellbeing, social well-being has three dimensions, material, subjective and relational that together constitutes human welfare. Cyclones Sidr and Aila caused loss of different 'material' values for the fishing communities in several ways. Rising tidal waves, associated with cyclones washed away productive assets, housing, and standing crops in the field, employment opportunities in alternative occupations were also severely squeezed, that altogether rendered in income losses of the aftermath of cyclone Aila. Most fishers took shelters in makeshift built on embankments that severely degraded their standard of living. Increased salinization after cyclone struck caused acute crisis of drinking water and loss of biodiversity that reduced overall environmental quality of region. Many fishers expressed their shocks, fears after seeing that rising water washing away their belongings before their eye. Living in constant economic hardship, depending on external supports for survival for longer period, school drop out and increased child labour undermined fishers' aspirations and confidence for a secured future. In case of relational values, 'social cohesion' of fishers' communities traditionally served as buffer during the period of crisis. However, individual competition to receive relief at the cost of others' interest negatively affected the community bonding and dispelled social capital to certain extent. The
responses from the government mostly gave emphasis on of materialistic rehabilitation of the affected communities. Following this new understandings through social well-being lens, the present study submits for a more holistic, more responsive policy making in Bangladesh by taking consideration into multiple dimensions of human welfare that are affected by climate change impacts.

P-1113-07

Characterization of extreme rain events
and assessment of Regional Climate
Models in Morocco

K. Khomsi (1); M. Gil (2); M. Sinan (3); M. Snoussi (4)

(1) Direction de la Météorologie Nationale, Casablanca, Morocco; (2) Université Montpellier 2, Hsm/ird, MONTPELLIER, France; (3) Ecole Hassania des Travaux Paris, Casablanca, Morocco; (4) Université Mohammed V-Agdal, Faculty of Sciences, Rabat, Morocco

At a global scale, more than half of the costliest disasters are weather related and our planet is facing more devastating extreme events mainly those related to rain. In Morocco, the floods between the 21st and the 25th November 2014 in the south of the country had caused the death of 32 people. In Casablanca, the flood of the 29th-30th November 2010 had caused enormous human and material losses. In the province of Settah, the flood of the 24th December 2001 have caused the death of eight people and flooded several industrial units and Darou in the region, adding to many other tragedies in the flood areas. Also in Ouira, the floods of the 17th August 1995 had caused more than 230 deaths, 550 missing, 200 damaged cars and other property damage. Thus, there is a real need for understanding and anticipating extreme weather events mainly those related to intense rains, that may lead the way in risk assessment and development of mitigation strategies.

The aim of this work is to characterize the frequency and
the trends of rain extreme events and to assess simulations
of regional climate models for these extreme events in
the watersheds of Tensif and Bouregreg (Morocco), during the
last decades. First, the work analyzes the observed trends
in daily rainfall time series, that it identifies very rare,
very exceptional rain events using percentile-sampling
thresholds, and studies the trends of regional frequencies.
Finally it evaluates an ensemble of regional climate models
from the European project ENSEMBLES, with regard to
the found trends in order to recognize models that best
describe observed rain regime, in the studied catchments.

P-1113-08

Relationship between the Tropical South Atlantic SST and drought over West Africa from CORDEX

NAB. Klutse (1) ; A. Babatunde (2) ; M. Adeniyi, (3) ; F. Nkrumah (4)

(1) Ghana Atomic Energy Commission, Remote sensing, gis, climate, Ghana space science and technology institute, Ghana, (2) University of Cape Town, Environmental And Geographical Science, Cape Town, Western, South Africa; (3) University of Ibadan, Department of physics, Ibadan, Nigeria, Federal Republic of; (4) University of Cape Coast, Department of physics, Cape Coast, Ghana

Droughts in West Africa are not only an environmental problem but also a social and economic concern. However, droughts research has not obtained the necessary attention in West Africa. Moreover, the dynamics of West African drought are not fully understood and among the studies that have considered droughts of West Africa, only a few have considered the link between Tropical South Atlantic (TSA) Sea Surface Temperature (SST) and drought over West Africa. In this study, we look at how CORDEX models represent the relationship between the TSA SST and drought, precipitation and temperature over West Africa. Studies on drought done over West Africa used only precipitation in Standardised Precipitation Index (SPI) to measure drought index. The use of precipitation alone is inadequate to give information about drought as evapotranspiration has a direct influence on drought. We recognize that evapotranspiration is an important process of water loss. Here, we use the Standardised Precipitation Evapotranspiration Index (SPEI) where evapotranspiration

is included in the calculation of the drought index.

P-1113-09

Drought Hazard Analysis over India and Its
Impact on Climate Using Applying Multiva-
riate Technique for Composite Indicators

P. Kumar, (1); K. Swati (2)

(1) Banasthali University, Remote sensing, jaipur, India; (2)
Banasthali University, Remote Sensing, Tonk, India

Drought being complex and least understood disaster affects multidimensional parameters of social and economic structure of society. It is said to be hydro-meteorological disaster having prolonged period of below average precipitation causing drought whose severity is largely determined by the amount of rainfall. The objective of this study is to evaluate the effect of drought hazard analysis in India with a combination of drought indices in geospatial environment using meteorological drought hazard analysis has been carried out effectively by the generation of Drought Hazard Index (DHI). Meteorological drought hazard analysis was performed by analyzing rainfall and its distribution pattern and drought occurrences. The current study of this research is to develop a composite index capturing spatial variations of drought hazard by taking into account the spatial and temporal occurrence of meteorological drought and to map the drought hazard in India. The present research involves generation of drought hazard index formed by compilation of individual indicators based on meteorological parameters into single index which is further used for the analysis of namely meteorological drought hazard in the country India. The study uses Climate Precipitation Center (CPC) rainfall time series at 10 x10 km grid for south west monsoon season (June-September) for 12 years 2001-2012 shown in Figure 1. DHI proposed in this study is a major initiative towards generating hazard indices for disasters with the composite index approach. DHI has fairly well represented the drought hazard pattern in the country by capturing the spatial variations in drought hazard across India. The DHI has thus effectively captured the spatial variations in drought hazard across India. The spatial patterns of drought hazard are reasonable and justify the strength of the index. The conclusion of this study is that there is evidence from further improved by adding more number of indicators. The strengths of the methodology are using a composite index method, analysis in spatial perspective, inclusion of a wide range of inputs and covering a large geographic area. Indicators selection and weights generation are the possible areas for further work.

P-1113-10

Determining climate indicators to assess
the impact of extreme weather events on
road accidents in Hungary

M. Lakatos (1); E. Vincze (1); Z. Bihari (1); T. Szentimrey (1)

(1) Hungarian Meteorological Service, Climate Department, Budapest, Hungary

The Special Report of IPCC on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (2011) concluded that there is evidence from observations gathered since 1950 of change in some extremes. A set of climate indices are used in several projects on climate change as prevailing indicators of changes in extremes.

The main focus of the presentation is preparing climate
indicators to impact and vulnerability assessment
of roads accidents, critical infrastructure, within
extreme weather events in wintering periods based on
existing data of the National Adaptation Geographical
Information System (NAGIS) in Hungary. The daily grid for
period 1961-2010 in 0.1° spatial resolution for several
basic meteorological variables and climate indicators
were created in CARPATCLIM (Climate of Carpathian
Region) project is integrated to the NAGIS system for the
territory of Hungary. The common used methods and
software in the CARPATCLIM project was the method
MASH (Multiple Analysis of Series for Homogenization;
Szentimrey) for homogenization, quality control,
completion of the observed daily data series; and the
method MISH (Meteorological Interpolation based on Surface Homogenized Data Basis; Szentimrey and Bihari) for gridding of homogenized daily data series. It is a relevant climate database for studying climate extremes and climate change in the region.

Different climate indicators are defined and quantified to mapping of exposure and sensitivity such as zero crossing days, precipitation amount in a specific period, ice days, precipitation amount in a specific period, cold/wet days, daily mean temperature < 25th percentile, and daily precipitation > 75th percentile for example. These climate indicators are the input values to impact studies that will be developed through the integration of the exposure and sensitivity mapping layers to the NAGIS system. Mapping of exposure will be based on measurement data and climate modelling results of Hungarian Meteorological Service (OMSZ), while the transport accident data recorded at the central body of disaster management will serve as a basis for sensitivity mapping. Among others these climate indicators will be used to assess the vulnerability due to climate change, which will foster the development of adaptation strategies and objective decision making.

## P-1113-11

### Changes in nature of extreme rainfall in southern Africa

#### C. Lennard (1)

(1) University of Cape Town, Climate System Analysis Group, Cape Town, South Africa

Extreme rainfall, usually expressed through local or national events, is driven by synoptic-scale forcinings as well as other factors like moisture availability, lapse rate etc. Rainfall and especially small-scale extreme rainfall associated with convection is poorly simulated by numerical models (general circulation models - GCMs) and regional climate models (RCMs). However, numerical models are able to simulate large-scale circulation states so in this study we characterize circulation states to investigate projected changes in extreme rainfall over Southern Africa.

Downscaled evaluation and projection data from two CORDEX regional models and four global models were examined and changes in the occurrence of rainfall and extreme rainfall investigated in three sub-regions over southern Africa. Synoptic states associated with extreme rainfall were identified in each region. Over the evaluation period we find that the regional models performed adequately in predicting the general rainfall characteristics over the region but did not capture the characteristics of extreme rainfall well. However, synoptic states associated with rainfall and extreme rainfall were captured and characterized.

In the near-term (2036–2065) and far-term (2065–2099) under both RCP4.5 and RCP8.5, synoptic states that are associated with drier conditions are projected to increase, while synoptic states that enhance precipitation are projected to decrease over time. Furthermore, the synoptic states associated with extreme precipitation are projected to increase.

Given the current threat posed by extreme rainfall in the regions these results speak directly to the necessity to develop effective and implementable adaptation strategies to reduce the impact of extreme rainfall on vulnerable communities.

## P-1113-12

Summer temperature extremes over Europe obtained from an ensemble of regional climate models

S. Lidija (1) ; I. Güttler, (1) ; K. Cindri ☐ Kalin, (1) ; ☐ Branković, (1)

(1) Meteorological and Hydrological Service, Department for Climatological Research and Applied Climatology, Zagreb, Croatia

European summer temperature extremes from simulations of six EURO-CORDEX regional climate models are analysed for the 20-year period, 1989–2008. The models were driven by ERA-Interim reanalysis at 50 and 12.5-km horizontal resolutions. Three categories of extreme temperature indices – absolute, percentile and duration – are derived from daily data. The results are compared with

extreme temperature indices calculated from the gridded daily E-OBS data over Europe and for Croatia, where the indices are derived from daily observations at 20 Croatian meteorological stations. The ensemble spread is large, but the biases at 12.5-km simulations are smaller than at 50 km. When compared with validation data, model simulated temperatures and their percentiles are mostly overestimated over southern Europe and underestimated over northern Europe. Over Croatia, spatial distribution of indices at 12.5 km is time scales (up to 6 months) and for stations above 10°N, the gamma distribution is the most frequent choice; below this belt, the Weibull distribution predominates. For longer than 6-month time scales, there are no consistent patterns of fitted distributions. After calculating the SPI in the usual way, operational drought thresholds that are based on an objective method are determined at each station. These thresholds are useful in drought-response decision making. From SPI time series, episodes of severe and extreme droughts are identified at many stations during the study period. Moderate/severe drought occurrences are intra-annual in short time scales and interannual for long time scales (greater than 9 months), usually spanning many years. The SPI calculated from CRU gridded precipitation shows similar results, with some discrepancies at longer scales. Thus, the spatialized dataset can be used to extend such studies to a larger region—especially data-scarce areas.

## P-1113-13

### Standardized Precipitation Index (SPI) and Its Use to Assess Drought Occurrences in Cameroon over Recent Decades

#### F. Mkankam Kamga (1)

(1) Université des Montagnes, Bangangté, Cameroon

The standardized precipitation index (SPI) is computed and analyzed using 55 years of precipitation data recorded in 24 observation stations in Cameroon along with University of East Anglia Climate Research Unit (CRU) spatialized data. Four statistical distribution functions (gamma, exponential, Weibull, and lognormal) are first fitted to data accumulated for various time scales, and the appropriate functions are selected on the basis of the Anderson-Darling goodness-of-fit test. The gamma scale is up to 6 months and for stations above 10°N, the gamma distribution is the most frequent choice; below this belt, the Weibull distribution predominates. For longer than 6-month time scales, there are no consistent patterns of fitted distributions. After calculating the SPI in the usual way, operational drought thresholds that are based on an objective method are determined at each station. These thresholds are useful in drought-response decision making. From SPI time series, episodes of severe and extreme droughts are identified at many stations during the study period. Moderate/severe drought occurrences are intra-annual in short time scales and interannual for long time scales (greater than 9 months), usually spanning many years. The SPI calculated from CRU gridded precipitation shows similar results, with some discrepancies at longer scales. Thus, the spatialized dataset can be used to extend such studies to a larger region—especially data-scarce areas.

## P-1113-14

### Analysis of extreme temperature indices of long-term homogenised temperature series in South Africa

#### M. Nxumalo (1) ; A. Kruger, (2)

(1) South African Weather Service, Climate department, Pretoria, South Africa; (2) South Africa, Climate department, Pretoria, South Africa

Homogenized data reduces the risk of significantly biased results in historical climate trend analysis. This study utilises for the first time long-term homogenised maximum and minimum daily temperature data sets for South Africa, spanning from the period 1931 to 2014. Previous extreme temperature trend analyses for South Africa only covered periods from 1961, which makes the current analyses significant in terms of the period of analysis, but also the number of stations that could be utilised. Whereas previous studies covered the analyses of the time series of fewer than 30 stations, the combinations of data from different stations in single time series through homogenisation increased the number of time series to 36. The time series were analysed using the extreme temperature indices developed by the WMO-ETCCDI team, which makes it possible to compare the results to other analyses across the world. Examples of the index trend analyses are the annual number of cool days, annual number of warm days, Diurnal temperature range, annual maximum and minimum temperatures, warm and cold nights and annual maximum warm spells, amongst others. This analysis forms part of the ongoing study in historical temperature trends in South Africa from in-situ measurements, by the South African Weather Service.

## P-1113-15

### Characterizing and understanding the