bluuebunny/crossref_metadata_2025 huggingface dataset:
Composition Dependence of Stratospheric Aerosol Radiative Forcing
Authors: Li Yaowei , Dykema John , Keutsch Frank
Published: March 2021

Model results suggest organic aerosol represents a significant fraction of total stratospheric aerosol radiative forcing, which in itself could represent as much as a quarter of global radiative forcing. Other model investigations suggest that the radiative influence of organic aerosols and dust must be included to obtain consistency with satellite measurements of stratospheric aerosols. In situ observations suggest that stratospheric aerosol composition is strongly vertically dependent and contains a significant organic component in the lower stratosphere. Laboratory studies suggest a range of possible values for the complex refractive index of organic aerosols in the stratosphere. The real part of the refractive index could vary over a range that brackets the value of the real refractive index for pure sulfuric acid/water aerosols. The imaginary part of the refractive index of the organic component is highly uncertain, suggesting aerosols that range from being purely refractive to significantly absorbing (eg, brown carbon). The mixing state of these mixed composition aerosols is also uncertain; depending on the complex refractive index of the organic component, morphological variation could have a significant influence on aerosol radiative properties. In this work we perform a sensitivity study of shortwave radiative forcing of stratospheric aerosols, examining the influence of different plausible values of complex refractive index and particle morphologies. In situ measurements of aerosol size and composition are used to represent the size distribution, vertical profile, and organic mass fraction for the computation of aerosol optical properties. These profiles of aerosol optical properties are used as inputs to a radiative transfer model to calculate profiles of shortwave fluxes and radiative heating rates for standard model atmospheres. The implications of the variations in aerosol optical depth and resulting radiative forcing are interpreted in terms of implications for satellite measurements of stratospheric radiative forcing. The various radiative forcing results and remote sensing implications for different scenarios of organic complex refractive index and morphology call for better understandings of the effects of chemical evolution and transport dynamics on the aerosol optical properties in the stratosphere.
Hurdles for implementation of constructed wetlands as Nature-based Solutions in Sweden
Authors: García Murcia Julián Andrés , Jaramillo Fernando , Wikström Sofia
Published: March 2021

Eutrophication in the Baltic Sea has been one of the major environmental issues during the last century partly due to extensive land-use change, loss of natural retention systems, and insufficient management. European legislation such as the Water Framework Directive (WFD) attempts to guide the recovery of good ecological status from freshwater to the sea, and suggests wetlands as ecosystems that can potentially contribute to achieving this goal. Wetlands are considered remarkable Nature-based Solutions (NbS) for improving water quality by diminishing the nutrient loads. This study aims to set a background context of the WFD implementation in Sweden, determine the status of constructed wetlands, and evaluate the stakeholders’ perspectives to identify the main administrative hurdles of wetland implementation in Sweden. For this purpose, we conducted a narrative review, database analysis, and semi-structured interviews with members of the institutions involved in water management. Our results show that it is essential to find synergies among the WFD and other directives to expand cross-sectoral cooperation, implement adjustments on the funding scheme that includes restoration and maintenance of natural wetlands, and increase compensation periods and cost ceiling. Likewise, it is crucial to perform significant improvements in the monitoring system, including more frequent data collection, as well as exploring new strategies to capture landowners’ interest in the implementation of NbS, such as the Catchment Officers program. Finally, we suggest paludiculture as a promising farming practice to increase proprietors’ attention on novel market alternatives, and in turn, to provide benefits for climate, water, and biodiversity.

Keywords Wetlands management · Water Framework Directive · Nature-based Solutions · Eutrophication · Semi-structured interviews · Sweden
Assessing changes in land use and their effects on river flows in tropical catchments of Ecuador
Authors: Giler-Ormaza Andy , Pimentel Rafael , Aguilar Cristina
Published: March 2021

Changes in land use and land cover (LULC) can have direct effects on streamflows at the catchment scale. However, studies of this type are still lacking in some tropical areas of the globe where LULC changes constitute the main antropic changes at watershed scale; for instance, deforestation, and agricultural modification among others. Therefore, for analysing impacts on streamflow, the first challenge is to achieve a good characterization of LULC. 

Here the objective is to evaluate whether these changes have occurred for two small basins on the South American coast in Ecuador (Junín and Paján) and, to analyse their possible effects on flows with special emphasis on minimum flows. Both catchments are characterized by savanna (Aw) climate with  seasonal rainfall patterns and a long period of minimum to zero precipitation. Changes in LULC are studied using two sources of remote sensing information: ESA-CCI-LC at spatial resolution of 300 m and Landsat TM at spatial resolution of 30 m, together with local authorities reports within the last decades. While ESA-CCI-LC directly provides LULC information , LULC was retrieved from surface reflectance after preprocessing (atmospheric and topographic corrections) from Landsat by  using a supervised algorithm. In a preliminary approach the observed changes are compared with variation in streamflow in the outlet of both catchment. 

Results show that for one of the catchments, Junín, ESA-CCI-LC does not reflect changes, while the analysis with Landsat TM shows a decrease of 11.7% of evergreen forest and an increase in agricultural activities. For the other basin, Paján, the first source indicates an increase in evergreen forest, while the second source indicates the opposite, a decrease of 7.4%. The contradictions in these sources highlight the importance of taking into account local knowledge as well as the appropriate selection of spatial resolution in the analysis. Finally, regarding the effects of the LULC changes in streamflow the initial approach was not sufficient to capture any direct effect and therefore, a deeper analysis based on specific features of the streamflow signal are planned as the next step.  
Understanding soil moisture dynamics through cosmic rays: a global analysis
Authors: Power Daniel , Rosolem Rafael , Rico-Ramirez Miguel , Desilets Darin , Desilets Sharon
Published: March 2021

Despite its importance in many hydrological and environmental applications, direct estimates of soil moisture at the field-scale is still challenging. The spatial gap between point scale sensors and satellite derived products is becoming increasingly important to consider in the push for hyper-resolution (sub)kilometre-hydrometeorological models. Cosmic-Ray Neutron Sensors (CRNS) can help to bridge this spatial gap. CRNS provide estimates of field-scale (sub-kilometre) root-zone integrated soil moisture typically at hourly intervals. They achieve this by counting fast neutrons which are produced in the atmosphere from incoming cosmic rays. Fast neutrons are mitigated primarily by hydrogen atoms, and it is this relationship that allows us to estimate field averaged soil moisture. National networks of CRNS are available in the USA, Australia, the UK, and Germany, along with individual sites across the globe. As these networks have expanded, so has our knowledge on best practices for calibration and correction of the sensor measurements. However, there continues to be a divergence and lack of harmonization in some processing data methods leading to an additional uncertainty when comparing sensors in different networks. This can undermine efforts to employ large-sample hydrological analysis of CRNS across a wide range of climate and biomes. To provide an easily accessible platform for multi-site comparison worldwide, we developed the Cosmic Ray Sensor Python tool (crspy). Crspy is an open-source Python package which is designed to process CRNS data from global networks in a uniform and harmonized way (https://www.github.com/danpower101/crspy). Additionally, crspy has been developed for multi-site ‘big-data’ analysis in hydrology. Our crspy tool produces detailed information in the form of metadata for each site, using both site specific data as well as global data products to give information on soil properties (SoilGridsv2), land cover/aboveground biomass (ESA CCI) and climate data (ERA5-land). Our preliminary analysis and tool development was carried out using data from more than 100 sites globally from the public domain. We will present an analysis of this large sample of data, utilising the harmonized soil moisture readings along with detailed metadata for each site. We aim to increase our understanding of the dominant mechanisms controlling soil moisture dynamics which will undoubtedly be useful in multiple areas of research such as catchment classification, agriculture and irrigation, and hydrological model development.
Uplifted marine terraces of Cephalonia island, Western Greece. Insights into the late Quaternary geomorphic evolution of the area.
Authors: Tsanakas Konstantinos , Saitis Giannis , Evelpidou Niki , Karymbalis Efthimios , Karkani Anna
Published: March 2021

Uplifted marine terraces act as a continuous record of eustatic changes in tectonically active coastal areas and can provide significant insight into their late Quaternary geomorphic evolution. Cephalonia island, located at the north-west edge of the Hellenic Arc, is a tectonically and seismically highly active area in the Ionian Sea, western Greece, where collision, subduction and transformation take place in a relatively small region. Pleistocene eustatic sea level fluctuations and the long-term vertical movements of the island, have left their imprint on the southern part of the island in the form of uplifted marine terraces. In the present study we aim to identify and map in detail the uplifted marine terraces, applying Digital Elevation Model analysis, utilizing GIS techniques and extensive fieldwork. A GIS spatial geodatabase has been organized and a GIS-based Automatic Landform Analysis was implemented for the identification and mapping of the inner edge of the uplifted marine terraces. Extensive field work and UAV imagery, enabled us to validate the results of the DEM analysis and to improve the accuracy of the position of the inner edges. A sequence of eight marine terraces has been revealed in the Paliki Peninsula ranging in elevation between 2-16 m above sea level for the lowest terrace and 300-440 m asl for the higher one. In the southern part of the main island 9 marine terraces have been identified and mapped at elevations ranging from 1-2 m for the lower one up to 142-170 m above sea level for the higher one respectively. The majority of the terraces is curved on erodible Pliocene and Pleistocene formations and only the lower ones appear to be well preserved. Their lateral morphological continuity is interrupted by the fluvial activity of a large number of ephemeral streams. The non-uniform occurrence of marine terraces at different elevations in Paliki peninsula and the southern part of the main island implies a complex tectonic activity of the island probably attributed to different tectonic blocks.
Detecting and analyzing regional trends in sub-daily rainfall annual maxima by using the Meta-statistical Extreme Value Distribution
Authors: Dallan Eleonora , Zaramella Mattia , Borga Marco , Marra Francesco
Published: March 2021

Global warming is expected to modify the regime of extreme precipitation. Physical laws translate increasing atmospheric heat into increasing atmospheric water content that, together with changes in the atmospheric dynamics, drive precipitation changes. The literature generally agrees that extreme precipitation is changing. However, the study of observed annual maximum time series suggests that trends are highly variable in space and uncertain, also as a result of the inherent large stochastic uncertainty of rainfall maxima. In the present work, we exploit the Meta-statistical Extreme Value (MEV) Distribution to investigate the statistical processes behind these trends and understand how they can be related to changing meteorological conditions. The MEV framework was recently proposed for the frequency analyses of extremes under pre-asymptotic conditions and was shown to significantly improve estimation uncertainty for extreme events by using ordinary events. The narrow confidence interval characterizing MEV is a clear advantage for trend analysis, and its ability to separate storm intensity and yearly occurrence permits to better understand the statistical processes underlying extremes. We gathered data from 33 stations in the Trentino region (Eastern Italian Alps) with at least 25 years of 5-minute resolution records (average density 1/190 km-2) and computed the parameters describing the yearly intensity distribution of events at multiple durations ranging from 15 minutes to 24 hours as well as their yearly number. The Regional Mann-Kendall test is used for evaluating the presence of trend in the distribution parameters, number of events per year, estimated quantiles and recorded annual maxima. Results confirm the presence of significant trends in the annual maxima. Trends in the 2-year quantiles estimated yearly using MEV are consistent with the observed trends in annual maxima, which are more marked for 15min to 1 hr duration and less marked for 3hr to 24 hr duration. Conversely, trends in rare quantiles (10-year, 100-year) are significant for durations up to 1 hour and become not significant for longer durations. Analysis of the parameters shows that these trends are likely due to a combination of (i) increasing number of storm events per year and increasing intensity of the storms, and (ii) changes in the tail properties of the storms.
Non-invasive imaging of CO2 and O2 concentration reveals hotspots of root respiration 
Authors: Bereswill Sarah , Rudolph-Mohr Nicole , Oswald Sascha E.
Published: March 2021

Root respiration constitutes a major contribution to the CO2 efflux from vegetated soils. Amongst temperature, soil moisture is a key environmental variable determining respiration in soils, because it affects the amount of oxygen available for respiration as well as the CO2 gas transport within the soil pore space.

Non-invasive imaging techniques facilitate the in situ observation of the complex respiration patterns in the rhizosphere. We applied planar optodes (80x100 mm²) to map the CO2 and O2 concentration in the rhizosphere of white lupine plants (Lupinus albus) grown in slab-shaped glass rhizotrons (150x150x15 mm³) in sandy soil under P-deficient conditions. Respiration was measured daily for 19 days after planting at constant soil moisture content as well as during a drying-rewetting experiment, during which soil volumetric water content varied between 0.1 and 0.3 cm³ cm-3.

During their development, the plants exhibited a heterogeneous spatial pattern of root respiration; the highest CO2-concentrations were measured at the root tips and along younger parts of the root system. Heterogeneity in CO2 and O2 patterns was most pronounced in the drying-rewetting experiment: Distinct hotspots of CO2-release and oxygen consumption emerged 30 to 60 minutes after watering. The hotspot-regions correlated with the location of cluster roots growing close to the optodes, where up to three times increased CO2 concentrations occurred. Overall CO2 concentrations in the bulk soil increased as CO2 accumulated over time as gas diffusion in the wet soil was limited.

Our results highlight the strong spatial and temporal variability of root respiration throughout the growth and development of the root system, and particularly in response to an increase in soil moisture. Further experiments aim to combine CO2 and O2 optode measurements with neutron computed laminography, a tomographic imaging method suited to capture the 3D root system architecture of plants grown in laterally extended rhizotrons in order to link root respiration to root branching order, diameter and functional type.
Evolution of a debris-covered glacier in the Kerguelen Archipelago (49°S, 69°E) over the past 15,000 years constrained by in situ cosmogenic 36Cl dating
Authors: Jomelli Vincent , Charton Joanna , Schimmelpfennig Irene , Verfaillie Deborah , Favier Vincent , Mokadem Fatima , Gilbert Adrien , Brun Fanny , Aumaître Georges , Bourlès Didier L. , Keddadouche Karim
Published: March 2021

Debris-covered glaciers constitute a substantial part of the worldwide cryosphere (Scherler et al. 2018). However, their long-term response to multi-millennial climate variability has rarely been studied, in particular in the Southern Hemisphere. The presence of both debris-covered and debris-free glaciers on Kerguelen Archipelago (49°S, 69°E) offers therefore an excellent opportunity to investigate and compare long-term evolution of these two types of glaciers. To do so, we used the cosmogenic 36Cl surface dating method on moraine boulders that allows to establish temporal constraints of glacier oscillation. We provide here the first Late Glacial and Holocene glacier chronology of a still active debris-covered glacier from the archipelago: the Gentil Glacier. Results show that the Gentil Glacier advanced once at ~14.3 ka, i.e. during the Late Glacial (19.0 – 11.6 ka), and re-advanced during the Late Holocene at ~2.6 ka (Charton et al., 2020). Both debris-covered and debris-free glaciers experienced a broadly synchronous advance during the Late Glacial, that may be assigned to the Antarctic Cold Reversal event (14.5 – 12.9 ka) (Jomelli et al., 2017; 2018). This suggests that both types (debris-covered and debris-free) of glaciers at Kerguelen were sensitive to large amplitude temperature fluctuations recorded in Antarctic ice cores (WAIS divide Project Members, 2013), associated with increased precipitations (Van der Putten, 2015). However, during the Late Holocene, the advance at about ~2.6 ka was not observed on other glaciers and seems to be a specific response of the debris-covered Gentil Glacier, either related to distinct ice dynamics or an individual response to precipitation changes.

 

 

Charton et al., 2020 : Ant. Sci. 1-13

Jomelli et al., 2017 : Quat. Sci. Rev. 162, 128-144

Jomelli et al., 2018 : Quat. Sci. Rev. 183, 110-123

Scherler et al., 2018 : GRL. 45, 11,798-11,805

Van der Putten et al., 2015 : Quat. Sci. Rev. 122, 142-157

WAIS Divide Project Members, 2013: Nature. 500, 440-444
Modeling shelter abundance for juvenile Atlantic salmon in a residual flow reach of a hydro power plant using SSIIM 2
Authors: Pritsis Spyros , Ruther Nils , Schwarzwälder Kordula , Stamou Anastasios
Published: March 2021

Nowadays, the aquatic biodiversity is highly under pressure due to anthropogenic changes of the rivers such hydraulic structures changing the diversity of flow and aquatic fauna as well as sediment continuity. This can have severe consequences on the fish population in the river reach. Fish are strongly depending on a certain substrate composition throughout all their life stages. Juveniles for example are depending on a certain availability of shelter in the substrate in order to survive this stage.

Therefore, we investigate the effects of changes in the sediment composition at a hydropower plant in Switzerland on the availability of potential shelter for juvenile fish. By utilizing the observed correlation between parameters describing the fine tail of a riverbed’s grain size distribution and shelter abundance for juvenile Atlantic salmon, we predict the available shelter in a river reach by using a 3D hydrodynamic numerical model directly coupled to a morphodynamic model. The initial substrate composition was assumed to be spatially uniform, its parameters based on a grain size distribution curve derived from collected sediment samples.

This model can now be used for habitat improvement scenario modeling. Based on the assumption that a specific mixture of sediment coming from upstream travelling through the river reach will positively influence the potential shelter availability, different scenarios can be investigated. The baseline for comparison was the simulation of the bed changes without any sediment supply from upstream. The baseline discharge was set to 100 m3 /s and was applied for 24 hours. The resulting bed changes create a map of the potential shelter availability of this grain size mixture. Then, two scenarios with sediment inflow from the upstream boundary were simulated. One coarse and one fine mixture of sediment were chosen as inputs, with the goal of investigating their impact on shelter abundance. The former designed to have a positive effect while the latter expected to reduce interstitial voids in the substrate and have a negative effect on available shelter.

The investigation is conducted as part of the EU Horizon 2020 funded project FIThydro (funded under 727830)
The «rainfall-runoff» system and its long-term fluctuations in the Siverskyi Donets River Basin (Ukraine)
Authors: Bolbot Hanna , Grebin Vasyl
Published: March 2021

The current patterns estimation of the water regime under climate change is one of the most urgent tasks in Ukraine and the world. Such changes are determined by fluctuations in the main climatic characteristics - precipitation and air temperature, which are defined the value of evaporation. These parameters influence on the annual runoff distribution and long-term runoff fluctuations. In particular, the annual precipitation redistribution is reflected in the corresponding changes in the river runoff.
The assessment of the current state and nature of changes in precipitation and river runoff of the Siverskyi Donets River Basin was made by comparing the current period (1991-2018) with the period of the climatological normal (1961-1990).
In general, for this area, it was defined the close relationship between the amount of precipitation and the annual runoff. Against the background of insignificant (about 1%) increase of annual precipitation in recent decades, it was revealed their redistribution by seasons and separate months. There is a decrease in precipitation in the cold period (November-February). This causes (along with other factors) a decrease in the amount of snow and, accordingly, the spring flood runoff. There are frequent cases of unexpressed spring floods of the Siverskyi Donets River Basin. The runoff during March-April (the period of spring flood within the Ukrainian part of the basin) decreased by almost a third.
The increase of precipitation during May-June causes a corresponding (insignificant) increase in runoff in these months. The shift of the maximum monthly amount of precipitation from May (for the period 1961-1990) to June (in the current period) is observed.
There is a certain threat to water supply in the region due to the shift in the minimum monthly amount of precipitation in the warm period from October to August. Compared with October, there is a higher air temperature and, accordingly, higher evaporation in August, which reduces the runoff. Such a situation is solved by rational water resources management of the basin. The possibility of replenishing water resources in the basin through the transfer runoff from the Dnieper (Dnieper-Siverskyi Donets channel) and the annual runoff redistribution in the reservoir system causes some increase in the river runoff of summer months in recent decades. This is also contributed by the activities of the river basin management structures, which control the maintenance water users' of minimum ecological flow downstream the water intakes and hydraulic structures in the rivers of the basin.
Therefore, in the period of current climate change, the annual runoff distribution of the Siverskyi Donets River Basin has undergone significant changes, which is related to the annual precipitation redistribution and anthropogenic load on the basin.
Understanding climate-related risks to infrastructure in Chinese cities, Climate Risk Assessment of Infrastructure Tool
Authors: Sunyer Maria , Parry Louise , Pritchard Oliver , Obrien Harriet , Kagan Astrid , Frost Laura , Smith Ben
Published: March 2021

Climate resilient infrastructure is essential for the safety, wellbeing, sustainability and economic prosperity of cities. An understanding of current and future climate risks is an essential consideration for the planning, design, delivery and management of new and existing resilient infrastructure systems. While there is a growing number of tools which focus on assessing specific components of climate risk there is a need for tools which help bridge the gap between climate science, resilience practitioners, infrastructure owners and policy makers.

The Climate Risk Infrastructure Assessment Tool developed within the Climate Science for Service Partnership China (CSSP China) aims to help planners and policy-makers understand how climate change may impact a city’s infrastructure systems. CSSP China seeks to bring together climate practitioners in China and the UK, and to forge links between climate scientists and industry practitioners to develop practical tools that translate the science into valuable insights for policymaking, planning and design. The development of this tools builds on earlier work carried out with the Shanghai Met Service and the British Embassy in Beijing to develop a qualitative tool to guide the assessment of climate risks for infrastructure.

The tool guides the user through a semi-quantitative climate risk assessment for a section of an infrastructure system. At present it uses ensemble data from global climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) to estimate and visualise future climate change projections helping cities understand the current and future likelihood of weather events. The tool then enables cities to assess the overall impact of severe weather on infrastructure by determining its vulnerability and criticality. Risk is estimated as a combination of event likelihood and impact. For key risks, guidance on implementing appropriate adaptation measures is provided to support planners and policy-makers to consider what action is needed.
Identification of meteo-hydrological extreme events at the regional scale: the Northwestern Italy case study
Authors: Pesce Matteo , Viglione Alberto , Borre Alessandro , Gabellani Simone , von Hardenberg Jost , Ganora Daniele
Published: March 2021

Extreme value theory (EVT) is commonly applied in hydrology to study extreme events. The univariate approach has been widely used in literature on this topic, but this limits the analysis to single sites. A more recent approach considers multivariate techniques applied to larger datasets, to detect the spatial structure of these events. However, how to properly define events and which variables should be considered for their identification and characterization in a regional domain is still a matter of debate. Moreover, recent studies have pointed out the increasing need of establishing connections between the different processes entering the hydrological cycle at larger spatial scales, especially in the context of global climate change. This work presents a non-parametric method for extracting the largest hydrological events occurring over the Northwestern Italy in the last decades and correlates them to spatially averaged extreme climate indices (ETCCDI). In particular, the extraction of extreme hydrological events started from the calculation of the empirical non-exceedance probability of the daily runoff values, at each station of the stream gauge network, and of a corresponding empirical return time. Then, a daily regional return time was determined by averaging the return time values over all stations for each day, with a sliding time window and site-related weights. Finally, the local maxima of the regional return time were extracted by intersecting the signal with a filter of the return time itself and the largest annual event was considered for each year. The spatial dependence of these events was analysed by extracting the local maximum discharge values at each station, corresponding to the occurrence of the maximum regional return times. A correlation with regional values of the ETCCDI indices was also performed to get some insights on the meteorological extremes playing a role in the formation of floods. Results show a rank of the extracted events for the study area and some considerations on their relative impact in terms of damage are provided. This gives an indication of the long-term variability of extreme events at the regional scale.
The DUST^2 Project: A source-to-sink investigation of the modern dust system in southwestern North America
Authors: Munroe Jeffrey , Brahney Janice , Carling Greg , Hahnenberger Maura , Perry Kevin , Skiles S. McKenzie
Published: March 2021

The DUST^2 project is a new Critical Zone Thematic Cluster funded by the US National Science Foundation.  DUST^2, an abbreviation for Dust across a Desert-Urban-Summit Transect, will study the modern dust system in southwestern North America, from source to sink using a combination of methods.  Previous work has demonstrated that arid lands in the southwestern US are significant sources of mineral dust.  The amount of dust emitted increased notably following European settlement, and climate models predict future increases in dust emission in response to climate warming.  This dust is transported to the north and east by the wind, particularly during the springtime and coincident with the passage of strong frontal systems.  The properties of this natural dust are altered as it mixes with anthropogenic aerosols sourced from industry and other activities along the densely populated Wasatch Front in northern Utah.  Eventually, this dust is delivered to mountain ranges at the eastern border of the Basin and Range as well as in the Rocky Mountains.  There, dust impacts the albedo of snowpack, triggering changes in snowmelt timing and magnitude.  Dust also influences the developmental trajectories of mountain soils and alters the nutrient status of mountain ecosystems.  The six primary investigators of the DUST^2 project, along with an array of additional staff and students, will study this dust system with field and lab-based methods focused on dust emitting landscapes, dust transport modeling, dust collection in urban and mountain settings, snow monitoring and snowmelt modeling, and investigation of dust-influenced soils coupled with analysis and modeling of the cycling of dust-derived nutrients.  A major goal of this project is to incorporate researchers beyond those responsible for establishing the overall project framework.  Anyone interested in learning about ways to collaborate or become involved with the DUST^2 effort should contact a member of the project leadership team listed as authors on this abstract.
Sensitivity of convective overturning and turbulent mixing of dissolved gases in the Labrador Sea to atmospheric forcing
Authors: Piunno Romina , Moore Kent
Published: March 2021

Deep oceanic convection occurs in few locations around the globe. One such location is found in the Labrador Sea where dense waters can subside to depths in excess of 2km below the surface. The weak stratification preconditions the water column for deep convection, triggered by wintertime surface cooling associated with high wind speed events. The convected water brings with it dissolved gases, such as Carbon Dioxide, which are in constant flux between ocean and atmosphere. It is thought that this process of turbulent boundary layer interactions coupled with deep convection is responsible for mixing these gases into the deep ocean, making the ocean the largest sink of anthropogenic carbon.

The convective overturning process depends on the temperature and salinity profiles which, together dictate density and thus the static stability of the water column. We have adapted a widely used one-dimensional mixed-layer model, referred to as PWP, to include a parameterization of the air-sea flux of gases such as Oxygen and Carbon Dioxide.  The model is forced with surface meteorological fields from the ERA5 reanalysis as well as the higher resolution operational reanalysis from the ECMWF.

With the model, we investigate the sensitivity of deep-water formation and the vertical profile of these gases to various atmospheric forcing scenarios. Overturning in the Labrador Sea is most active during the winter months when heat flux out of the ocean is at its maximum. It is found that overturning is far more sensitive to thermal forcing than it is to freshwater forcing within the range of forcings typical to the Labrador Sea. We explore the impact of this sensitivity, including the dependence of the atmospheric forcing on modes of climate variability such as the NAO,  has on the role that the Labrador Sea plays as a marine sink for anthropogenic carbon.
Seasonal prediction in northern Atlantic Ocean and Norwegian Seas
Authors: Keenlyside Noel , Pariyar Sunil , Bethke Ingo , Wang Yiguo , Counillon Francois
Published: March 2021

Recent operational systems are able to predict sea surface temperature (SST) on seasonal timescales in the extra-tropical North Atlantic and Nordic Seas to a high-degree and as high as in the tropical Pacific. While prediction on multi-year timescales is well documented, the source of the high skill on seasonal timescales is unclear and somewhat unexpected. Here, using the Norwegian Climate Prediction model, we show that the skill on seasonal timescales is associated primarily with low-frequency variability (timescales longer than five years). Consistently, there is high skill in predicting SST anomalies six seasons in advance, although there is a skill drop across boreal summer that seems associated with reduced vertical mixing. External forcing and initialized ocean variability contribute similarly to skill on seasonal timescales, as assessed through a heat budget analysis. Skill on these timescales can benefit fisheries and aqua culture.
Tropical forest CH4: from termite mounds to tower  measurements
Authors: van Asperen Hella , Warneke Thorsten , C De Araújo Alessandro , Forsberg Bruce , Ramos de Oliveira Leonardo , de Lima Xavier Thiago , Sá Marta , Teixeira Paulo , Azevedo de Oliveira Robson , Leal Leila , Moura Veber , Rafael Alves-Oliveira João , Botia Santiago , Lavrič Jost , Komiya Shujiro , Frumau Arnoud , Hensen Arjan , van Dinther Danielle , van den Bulk Pim , Notholt Justus
Published: March 2021

Methane (CH4) is one of the most important anthropogenic greenhouse gases.  Despite its importance, natural sources of methane, such as tropical wetlands and termites, are still not well understood and a large source of uncertainty in the tropical CH4 budget. The Amazon rainforest is a key region for the (global) CH4 budget but, due to its remote location, continous CH4 concentration and flux measurements are still rare.

The 50 m high K34 tower (field site ZF2) is located in a pristine ‘Terra Firme’ tropical forest region 60 km northwest of Manaus (Brazil), and is located next to a waterlogged valley, a possible location for anaerobic CH4 production. In October 2018, in addition to the existing EC CO2 system, an in-situ FTIR-analyzer (measuring CO2, CO, CH4, N2O and δ13CO2) was set up to measure tower profile concentrations, above and below the canopy, continuously. By analyses of vertical and temporal nighttime concentrations patterns, an emission estimate for all gases could be made, and an ecosystem emission of ~1 nmol CH4 m-2 s-1  was estimated. In addition, by use of different types of flux chambers, possible  CH4 sinks and sources such as soils, trees, water and termite mounds were measured.

By combining tower and flux chamber measurements, the role and magnitude of different ecosystem sources could be assessed. In this presentation, an overview of the measured CH4 forest concentrations and fluxes will be given.
Coherent intra-annual ensemble forecasts of surface and groundwater availability
Authors: Robertson David , Fu Guobin , Barron Olga , Hodgson Geoff , Schepen Andrew
Published: March 2021

In many parts of the world, surface water and groundwater are used complementarily to supply agricultural production and to meet urban water demands. Conjunctive management of these water resources requires balancing of the different characteristics of surface water and groundwater with respect to availability, quality and cost of supply. Ensemble forecasts of surface water and groundwater availability can inform management decisions but require explicit representation of the complex processes controlling surface and groundwater interactions. While many methods and operational services exist that provide independent forecasts for surface and groundwater availability, to our knowledge no approaches for coupled forecasting have been developed yet.

In this presentation we introduce an approach that generates coupled forecasts of surface water and groundwater availability. It extends the Forecast Guided Stochastic Scenarios (FoGSS) (Bennett et al., 2016) approach to forecast groundwater level at specified locations, in addition to streamflow totals, to lead times of 12 months at monthly time steps. We adapt a conceptual hydrological model to improve predictions of streamflow and, as a by-product, groundwater level. We then apply independent error models to streamflow and groundwater level to reduce bias, update predictions using recent observations and quantify residual uncertainty. Ensemble streamflow and groundwater forecasts are generated by forcing the hydrological and error models with ensemble rainfall forecasts generated by post-processing ECMWF System 5 outputs. The skill, bias and reliability of the rainfall, streamflow and groundwater level forecasts were assessed for a case-study catchment in South-East Queensland, Australia. We find that skill of forecasts is dependent on the forecast issue month and lead time, with groundwater level forecasts displaying significant skill to lead times of 12 months, while streamflow forecast skill rarely persists beyond 3 months.  We conclude by describing opportunities to improve forecast skill and some of the challenges that may be faced in the operational delivery of water resource forecasts in real-time.

Reference

Bennett, J. C., Wang, Q. J., Li, M., Robertson, D. E., and Schepen, A.: Reliable long-range ensemble streamflow forecasts: Combining calibrated climate forecasts with a conceptual runoff model and a staged error model, Water Resources Research, 52, 8238-8259, 10.1002/2016WR019193, 2016.
Precipitation over the Southern Ocean: synoptic analysis and model evaluation using ground-based remote sensing and in-situ measurements
Authors: Luis Diogo , Gorodetskaya Irina , Leonard Katherine , Schlosser Elisabeth , Vignon Etienne , Ralph F. Martin , Lehning Michael
Published: March 2021

Precipitation is still a poorly known variable in the Southern Ocean/Antarctica due to the lack of measurements. Unique precipitation measurements were carried out during the Swiss Polar Institute’s Antarctic Circumnavigation Expedition (ACE) (December 2016 - March 2017). High temporal resolution measurements of precipitation were performed by a Snow Particle Counter (SPC) and by a micro rain radar (MRR) aboard the RV Akademik Tryoshnikov. Radiosondes were launched periodically to observe the vertical structure of the atmosphere. Additionally, MRR and radiosonde measurements from Dumont D’Urville station (DDU) were available when the expedition was in the Mertz Glacier region. These data offer a rare opportunity to evaluate model and reanalysis products performance in a region without regular precipitation measurements. In this study, ECMWF’s ERA5 reanalysis product and Antarctic Mesoscale Prediction System (AMPS) model data are evaluated using ACE and DDU in-situ observations. Two snowfall events that occurred around Mertz Glacier during the ACE campaign were chosen to compare ERA5 and AMPS data with in-situ measurements. The first event on 2 February 2017 was associated with an extratropical cyclone east of Adelie Land and a moderate along-shore moisture transport. The second event on 8-10 February 2017 was associated with a cyclone west of Mertz blocked by a high-pressure ridge, directing an intense moisture transport (identified as an atmospheric river) and precipitation to DDU. To assess if ERA5 reanalysis and AMPS (Antarctic Mesoscale Prediction System using Polar-WRF model) are able to represent these different types of precipitation events, we analyse the differences in precipitation amount between in-situ, model and reanalysis data and compare modelled vertical profiles with radiosonde measurements.
Developing a triple tree-ring constraint for tree growth and physiology in a global land surface model
Authors: Barichivich Jonathan , Peylin Philippe , Daux Valérie , Risi Camille , Jeong Jina , Luyssaert Sebastiaan , Launois Thomas
Published: March 2021

Gradual anthropogenic warming and parallel changes in the major global biogeochemical cycles are slowly pushing forest ecosystems into novel growing conditions, with uncertain consequences for ecosystem dynamics and climate. Short-term forest responses (i.e., years to a decade) to global change factors are relatively well understood and skilfully simulated by land surface models (LSMs). However, confidence on model projections weaken towards longer time scales and to the future, mainly because the long-term responses (i.e., decade to century) of these models remain unconstrained. This issue limits confidence on climate model projections. Annually-resolved tree-ring records, extending back to pre-industrial conditions, have the potential to constrain model responses at interannual to centennial time scales. Here, we constrain the representation of tree growth and physiology in the ORCHIDEE global land surface model using the simulated interannual variability of tree-ring width and carbon (Δ13C) and oxygen (δ18O) stable isotopes in six sites in boreal and temperate Europe.  The model simulates Δ13C (r = 0.31-0.80) and δ18O (r = 0.36-0.74) variability better than tree-ring width variability (r < 0.55), with an overall skill similar to that of other state-of-the-art models such as MAIDENiso and LPX-Bern. These results show that growth variability is not well represented, and that the parameterization of leaf-level physiological responses to drought stress in the temperate region can be improved with tree-ring data. The representation of carbon storage and remobilization dynamics is critical to improve the realism of simulated growth variability, temporal carrying over and recovery of forest ecosystems after climate extremes. The simulated physiological response to rising CO2 over the 20th century is consistent with tree-ring data in the temperate region, despite an overestimation of seasonal drought stress and stomatal control on photosynthesis. Photosynthesis correlates directly with isotopic variability, but correlations with δ18O combine physiological effects and climate variability impacts on source water signatures. The integration of tree-ring data (i.e. the triple constraint: width, Δ13C and δ18O) and land surface models as demonstrated here should contribute towards reducing current uncertainties in forest carbon and water cycling.
Evaluating and Improving Parameterizations of the Variance of Temperature Fluctuations Over Heterogeneous Landscapes for Surface Boundary Conditions in Atmospheric Models
Authors: Waterman Tyler , Katul Gabriel , Bragg Andy , Chaney Nathaniel
Published: March 2021

The implementation of higher-order turbulence closure schemes in Earth system models (e.g., the Cloud Layers Unified by Binormals; CLUBB) aims to improve the modeling of convection and radiative transfer in numerical weather prediction and climate models. However, the added value of these schemes is constrained by the specification of boundary conditions on higher-order statistics. At the land surface, many of the higher order turbulence statistics that are required as boundary conditions are parameterized using formulations more appropriate for stationary and planar-homogeneous flow in the absence of subsidence. A case in point is the variance of the potential temperature fluctuations.  Because of the additive nature of variances arising from non-uniformity in surface heating, current parameterizations are not readily generalizable. The current scheme used in CLUBB, as well as other models, relies on limited studies over uniform terrain, with the variance entirely determined by local sensible heat flux, friction velocity, and the Obukhov stability parameter without regard to local site characteristics. This presentation aims to address this weakness by leveraging the National Ecological Observation Network (NEON) network of eddy covariance towers to validate the current parameterization scheme for potential temperature variance, as well as propose improvements for more heterogeneous terrain.

The turbulence fluctuations of temperature at 39 NEON sites are processed and quality controlled, removing points occurring at night, while precipitation is falling, and with sub-zero temperatures. Results overall indicate the current scheme performs well, especially over flat homogeneous terrain where local flux relationships dominate. When there is sufficiently heterogeneous, rough terrain or non-closure of the local energy balance, however, existing schemes fail to accurately estimate the variances in temperature. In these cases, the parameterization needs to be modified, and initial results suggest simple adjustments can yield improvements and reduce error close to that of the uniform sites with local energy balance closure. The successful improvement of the temperature variance parameterization scheme implies high potential for similar, new, empirically derived parameterizations for the surface boundaries for other higher order turbulent statistics (e.g. temperature skewness) in atmospheric turbulence models.