bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal variation of fault slip rate in southern Taiwan by integrating GPS and InSAR observations
Authors: Hsiao Li-Yang , Chang Wu-Lung
Published: March 2020

Due to the rapid convergence of Philippine Sea Plate toward the continental margin of Eurasian Plate, the southern Taiwan has a high number of 8 active faults published by the Taiwan Central Geological Survey. We inverted the Global Positioning System (GPS) velocity measurements to investigate the slip rates on these faults and how these values could change with time, especially before and after large seismic events. In this study we employed TDEFNODE to first evaluate two fault-slip models before and after the 2016 Mw 6.4 Meinong earthquake within the periods of 2002 to 2016 (model 1) and 2016 to 2018 (model 2). Our results from these two models show that some long-term average fault slip rates were changed with time, such as the Zuozhen, Chishan and Hengchun faults that have values 30.2, 27.0 and 29.7 mm/yr in 2002-2016 and 15.2, 6.6 and 14.2 mm/yr in 2016-2018, respectively. In addition, we focused on the Mw 7.0 and Mw 6.9 2006 Hengchun doublet earthquakes by integrating the Permanent Scattered Interferometric Synthetic Aperture Radar (PS-InSAR) data collected by ALOS from 2007 to 2011 with the GPS velocities for a joint inversion for fault slip model (model 3). The results show that the average long-term slip rates of the Chishan and Hengchun faults are 12.5 and 16.8 mm/yr, respectively, which are significantly lower than the rates of 2002-2016 (model 1). More fault models with different time spans are on the way to affirm these temporal rate changes and explore their implications on earthquake hazard analysis.
Multidisciplinary approach to assess landslide hazards in alpine environment: the geomorphological map of the upper Maira Valley (Western Alps, Italy).
Authors: Bonasera Mauro , Petroccia Alessandro , Caso Fabiola , Nerone Sara , Morelli Michele
Published: March 2020

The landscape evolution of the U-shaped Maira Valley was mainly led by glacial dynamics during Pleistocene. The Holocene linear fluvial erosion creates higher steepness slopes in a narrow valley in which gravitational phenomena involves buildings and facilities of Acceglio municipality (Piedmont, Italy). A geomorphological survey in an unmapped area of about 12 km2 has been carried out and a new map at scale 1:10000 has been realised. In order to improve the accuracy of fieldwork data, several multidisciplinary techniques have been investigated. The landforms and slope evolution were analysed by using a 5-meters resolution ARPA Digital Elevation Model (DEM) in GIS environment. Discontinuities and geomorphological features were recognized and mapped observing aerial-photos provided by Regione Piemonte. Multi-temporal dataset of orthophotos were useful to examine the river pattern behaviour coupled with interdigitating polygenic fan deposition. The stratigraphic sequence knowledge was achieved using boreholes, inclinometers and piezometers evaluating eventual detrital cover thickness. Detailed field investigations allowed to understand the relationship between structural geology and landslide evolution, in particular concerning several detachment zones characterising the slope overlooking Acceglio town. In the uppermost range of that slope, the fracturation is intense and influences the rock-falls and rock avalanches trigger, whilst debris flows were identified throughout the detected area associated with a homogeneous presence of weathered cover. Widespread accumulation bodies suggest how avalanche and debris flow occurrences have affected Acceglio human activities, testified by historical archives documents as well. In the past, several trial to mitigate these risks were performed through engineering activities which could be refined and implemented with further local analysis on landslide susceptibility. Research on this issue, in addition to having a great scientific interest, can provide essential tools for upper Maira Valley Administrations, being the main available support for an appropriate urban planning.
Impacts of stratospheric ozone and greenhouse gas changes on the Southern Hemisphere circulation in the CCMI models
Authors: Han Bo-Reum , Choi Jung , Son Seok-Woo
Published: March 2020

 The impacts of stratospheric ozone and greenhouse gas changes on the Southern Hemisphere (SH) climate are re-visited by examining the single forcing experiments from the Chemistry-Climate Model Initiative (CCMI) project. In particular, the fixed ozone-depleting substance (ODS) runs and the fixed greenhouse gas (GHG) concentration runs are directly compared with the reference runs for both the past and future. Consistent with the previous studies, the SH-summer general circulation changes, such as changes in the jet location, Hadley cell edge, and Southern Annular Mode (SAM), show the opposite trends from the past to the future in response to the Antarctic ozone depletion and recovery. The GHG-induced circulation changes largely enhance the ozone-induced circulation changes in the past, but partly cancel them in the future. The ozone recovery-related tropospheric circulation return dates are also estimated in this study. We will further discuss the inter-model diversity among the CCMI models.
Estimating Antarctic Ice Sheet Contributions to Future Sea Level Rise Using a Coupled Climate-Ice Sheet Model
Authors: Park Jun-Young , Schloesser Fabian , Timmermann Axel , Choudhury Dipayan , Lee June-Yi , Nellikkattil Arjun Babu , Pollard David
Published: March 2020

One of the largest uncertainties in projecting future global mean sea level (GSML) rise in response to anthropogenic global warming originates from the Antarctic ice sheet (AIS) contribution. Previous studies suggested that a potential AIS collapse due to the Marine Ice Sheet Instability (MISI) and Marine Ice Cliff Instability (MICI) may contribute up to 1m GMSL rise by the year 2100. However, these estimates were based on uncoupled ice sheet models that do not capture interactions between the AIS and the ocean and atmosphere. Here, we explore future GMSL projections using a three-dimensional coupled climate-ice sheet model (LOVECLIP) that simulates ice sheet dynamics in both hemispheres. The model was forced by increasing CO2 concentrations following the Shared Socioeconomic Pathway (SSP) 1-1.9, 2-4.5 and 5-8.5 scenarios. Over the next 80 years, the corresponding GMSL contribution from AIS amounts to about 2cm, 8cm and 11cm, respectively. Additional sensitivity experiments show that AIS meltwater flux in response to the SSP 5-8.5 CO2 concentrations causes subsurface Southern Ocean warming which leads to an additional 20% AIS melting and a reduction in Southern Hemispheric future warming.
Spatial and temporal variation of drought patterns over East Africa
Authors: Haile Gebremedhin Gebremeskel , Tang Qiuhong , Leng Guoyong , Jia Guoqiang , Wang Jie , Cai Diwen , Sun Siao , Baniya Binod , Zhang Qinghuan
Published: March 2020

Understanding historical patterns of changes in drought is essential for drought adaptation and mitigation.
While the negative impacts of drought over east Africa have attracted increasing attention,
a comprehensive and long-term spatiotemporal assessment of drought is still lacking. Here, we provided
a comprehensive spatiotemporal drought pattern analysis during the period of 1964–2015 over
the GHA. The Standardised Precipitation-Evapotranspiration Index (SPEI) at various timescales (1 month
(SPEI-01), 3 month (SPEI-03), 6 month (SPEI-06), and 12 month (SPEI-12)) was used to investigate drought
patterns on a monthly, seasonal, and interannual basis. The results showed that despite regional differences,
an overall increasing tendency of the drought was observed across the GHA over the past 52 yr, with trends of
change of -0.0017 yr-1, -0.0036 yr-1, -0.0031 yr-1, and -0.0023 yr-1 for SPEI-01, SPEI-03, SPEI-06, and
SPEI-12, respectively. Droughts were more frequent, persistent, and intense in Sudan and Tanzania, while
more severe droughts were found in Somalia, Ethiopia, and Kenya. Droughts occurred frequently before
the 1990 s, and then became intermittent with large-scale impacts occurred during 1973–1974, 1984–
1985, and 2010–2011. A turning point was also detected in 1989, with the SPEI showing a statistically significant
downward trend during 1964–1989 and a non-statistically significant downward trend from 1990
to 2015. Seasonally, droughts exhibited an increasing trend in winter, spring, and summer, but a decreasing
trend in autumn. The research findings have significant implications for drought adaptation and mitigation
strategies through identifying the hotspot regions over east Africa at various timescales. Area-specific
efforts are required to alleviate environmental and societal vulnerabilities to drought events.
Upscaling riparian lowland buffer zone flow dynamics in the Danish nitrogen model
Authors: Noorduijn Saskia , Højberg Anker
Published: March 2020

The importance of riparian lowland buffer zones on surface and ground-water quality has recently received greater attention within Denmark. Significant funding has been made available to re-establish riparian lowlands to reduce nitrate loading to streams, as well as reducing GHG emissions. Surface water nitrate loads are currently estimated using the national nitrogen model, the scale of this model is unable to capture the flow dynamics of small-scale riparian lowlands. Therefore, the model is unable to account for the spatial and temporal variation in the nitrate reduction in the riparian lowlands. Consequently, the current focus is on upscaling the hydrological impacts of riparian lowlands so they may be incorporated into the national scale model in a consistent and transparent way.

Key to quantifying the impacts of riparian lowlands on the surface water nitrate loading is partitioning flow pathways, e.g., surface runoff, groundwater discharge, and drain flow. For example, the likelihood of nitrate reduction within a riparian lowland dominated by surface runoff is low, conversely if groundwater discharge dominants the likelihood is higher. Determining a relationship between the small-scale riparian flow pathways and larger scale landscape features, such as drainage area, slope, and aquifer geometry, may provide a means to upscale and quantify the reduction capacity of a lowland riparian zone.

Numerous field scale riparian lowland investigations have focused on describing the hydraulic processes, but very few investigations have attempted to quantify the flow pathways and/or provide insight into how this information may be used at a larger scale. This investigation will aim to simulate and quantify the observed flow pathways at the field scale for two field sites in Jutland (Fensholt and Holtum), Denmark. These simulations will aid in identifying the keys landscape features which can be used to determine the reduction capacity of riparian lowlands at the national scale.
Links between global terrestrial water storage and large-scale modes of climatic variability
Authors: Li Tiewei
Published: March 2020

Large-scale modes of climatic variability, or teleconnections, influence global patterns of climate variability and provide a framework for understanding complex responses of the global water cycle to global climate. Here, we examine how Terrestrial Water Storage (TWS) responds to 14 major teleconnections (TCs) during the 2003–2016 period based on data obtained from the Gravity Recovery and Climate Experiment (GRACE). By examining correlations between the teleconnections and TWS anomalies (TWSA) data, we find these teleconnections significantly influence TWSA over more than 80.8% of the global land surface. The El Niño-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO) are significantly correlated with TWSA variations in 55.8%，56.2% and 60% the global land surface, while other teleconnections affect TWSA at regional scales. We also explore the TCs’ effect on three key hydrological components, including precipitation (P), evapotranspiration (ET) and runoff (R), and their contribution to TWSA variations in 225 river basins. It’s found the TCs generally exert the comprehensive but not equally impact on all three components (P, ET and R). Our findings demonstrate a significant and varying effect of multiple TCs in terrestrial hydrological balance.
Building loss ratio comparison based on physical vulnerability and event-based data in Taiwan
Authors: Hsu Chih-Hao , Tsao Ting-Chi , Huang Chuan-Yi
Published: March 2020

In this study, several debris flow physical vulnerability curves and the even-based inundation depth were applied to a mountainous community hit by debris flow in 2015 to estimate the various possible loss ratio of each building. Then the comparison between estimated possible loss ratio and loss ratio determined by expert in the field is made to map out the distribution and deviation.

Vulnerability is commonly related to the consequences of natural hazard. For debris flow hazard these consequences are generally measured in terms of losses (Fuchs et al., 2007). In risk management vulnerability is an essential component for analyzing natural hazard risks (Lo et al., 2012). It is expressed on a scale from 0 (no damage) to 1 (total loss) and increasing with the intensity of hazard.

The Taoyuan DF034 debris flow potential torrent is located in northern Taiwan. In 2015, during Typhoon Soudelor the rainfall caused a shallow landslide which was transformed instantly into a debris flow. 13,000 cubic-meter of debris were washed out and deposited in 5,200 sq-meter area. Because of the evacuation before debris flow event, only 15 residential houses were inundated and no one was injured fortunately. In order to understand the inundation depth, the field investigation was executed shortly after the event. The building dimension, floor, structure type, location, and inundation depth were well documented and the loss ratio of each building was determined by expert as well.

The comparison of loss ratio based on inundation depth and impact pressure between Kang and Kim (2016), Papathoma-Köhle et al. (2015) and Lo et al. (2012) is made. The result shows building characters and debris flow velocity affect the loss ratio significantly.

Key Words: Debris flow, Vulnerability, Loss ratio, Taiwan
Interpreting Coda Wave Decorrelation from ambient seismic noise interferometry, inputs from laboratory experiments
Authors: Larose Eric , Thery Romain , Abraham Odile , Guillemot Antoine
Published: March 2020

Seismic and ultrasonic waves are sometimes used to track fluid injections, propagation, infiltrations in complex material, including geological and civil engineered ones. In most cases, one use the acoustic velocity changes as a proxy for water content evolution. Here we propose to test an alternative seismic or acoustic observable: the waveform decorrelation. We use a sample of compacted millimetric sand as a model medium of highly porous multiple scattering materials. We fill iteratively the sample with water, and track changes in ultrasonic waveforms acquired for each water level. We take advantage of the high sensitivity of diffuse coda waves (late arrivals) to track small water elevation in the material. We demonstrate that in the mesoscopic regime where the wavelength, the grain size and the porosity are in the same order of magnitude, Coda Wave Decorrelation (waveform change) is more sensitive to fluid injection than Coda Wave Interferometry (apparent velocity change). This observation is crucial to interpret fluid infiltration in concrete with ultrasonic record changes, as well as fluid injection in volcanoes or snow melt infiltration in rocky glaciers. In these applications, Coda Wave Decorrelation might be an extremely interesting tool for damage assessment and alert systems [1].

 

[1] R. Thery, A. Guillemot, O. Abraham, E. Larose, Tracking fluids in multiple scattering and highly porous materials: toward applications in non-destructive testing and seismic monitoring, Ultrasonics, 102, 106019 (2019).
Spatial distribution of debris cover and its impacts in the Hunza River Basin
Authors: Zhang Yong , Liu Shiyin , Wang Xin
Published: March 2020

Hunza River is an important tributary of the Indus River, which contributes ~12% of the total runoff in the upper Indus River. 25% of Hunza River basin is covered by glaciers. The Karakoram Highway (KKH) connecting Pakistan and China goes from the Khunjerab Pass and down to the Gilgit, which is an important section of the Pakistan-China Economic Corridor in the high mountains. Many glaciers in this region are extensively covered by supraglacial debris, which strongly influences glacier melting and its spatial pattern. Changes in these glaciers may threaten the stability of the highway subgrade through meltwater floods, unpredictable behaviors of glacier terminals as well as potential outburst floods of glacier lakes near glaciers. Therefore, predicting runoff, response to climate change and risk of outburst floods of debris-covered glaciers requires different treatment to that of clean glaciers in the Hunza River Basin. In this study, we estimate the thermal resistance of the debris layer for the whole basin based on ASTER images. Our results reveal that debris-covered glaciers account for 69% and 30% of the total number and area in the basin. Using a physically-based debris-cover effect assessment model, we find different debris-cover effects on different glaciers, with important implications for the morphology and evolution of glacier hydrological system and associated hazards.
Preliminary Study on Fusion Scheme of Multi-dimensional and Multi-scale Potential Field Data
Authors: Ji Xiaolin , Wang Wanyin , Liu Fuxiang , Yang Min , Xiong Shengqing , Ma Jie
Published: March 2020

Gravity and magnetic surveys are widely used in geology exploration because of its advantages, such as efficient and economy, green and environment-friendly, widely coverage and strong horizontal resolution. In order to well study in the geology exploration, it is required to comprehensively combine the different scales (different scales data) and different dimensions (satellite data, aeronautical data, ground data, ocean data, well data, etc.) of gravity and magnetic data that were observed in different periods, however, the comprehensive application of the multi-dimensional and multi-scale gravity and magnetic data still stays in the initial stage. In this paper, we do research on the key point of the fusion of potential field data (gravity and magnetic data): the way to fuse the different scales and different dimensions of potential field data into a benchmark and the same surface. Based on this research, we propose a scheme to fuse the multi-dimensional and multi-scale gravity and magnetic data. The synthetic models show that this fusion scheme is able to fuse the multi-dimensional and multi-scale gravity and magnetic data with great fusion results and small errors, in addition, the most important is that the fusion data conform to the characteristics of the potential field data and can meet the needs of data processing in the following steps. One of case studies in China has been accomplished to fuse aeronautical and ground gravity data that are different scales by using this fusion scheme. The fusion scheme we proposed in this study can be used in the fusion of the multi-dimensional (aeronautical, ground and ocean) and multi-scale gravity and magnetic data, which is good for interpretation and popularization.
Slope Activity Analysis in the Rogun Catchment Area, Tajikistan, using Remote Sensing Techniques
Authors: Jones Nina , Manconi Andrea , Strom Alexander
Published: March 2020

The stability and lifetime of construction projects in mountain areas are strongly dependent on local slope activity. Hydropower projects in particular are often affected and endangered by landslide damming and flood wave generation due to slope failures, and thus extensive studies of ground surface instability are vital to assess associated hazards. The Rogun Hydropower Project HPP located in Tajikistan in the Vakhsh – Surkhob River network is currently under construction. The site lies within the seismically active Tien Shan and Pamir Mountain ranges of Central Asia and in particular the Peter the First Range. This region is marked by extreme topography, steep slopes and extensive valley networks and has experienced large and catastrophic slope failures in the past, of which a multitude have been triggered by earthquakes of magnitude M≥4. Co-seismic failures are thus common in the area and present a high geotechnical hazard; however, to date no information on active slope instabilities in its catchment area exists.

Here we present an inventory of slope instabilities in the Rogun Dam catchment area based on optical and synthetic aperture radar differential interferometry (DInSAR) remote sensing techniques. Sentinel-1 multi–temporal differential interferograms are generated for summer periods of 2016 – 2018 to detect surface displacements. Slope velocities are estimated based on a comparison between differential interferograms, while landslide types are identified based on a geomorphological classification. A likelihood analysis is developed to understand the state of activity of slopes and provide a semi-quantitative confidence thereof. The collected data is subsequently integrated to perform spatial and statistical analyses in order to perform a proximity analysis, assess a co-seismic link and evaluate the damming hazard potential to the Rogun HPP. Results show that a clear majority of detected features are located within 10 km of major faults and in zones of high peak ground acceleration, indicating a potential seismic influence or triggering. Some active slopes show an increase in surface displacement after a particular earthquake event and equally suggest a potential link. Moreover, we developed a damming hazard analysis for slopes detected as active in Sentinel-1 differential interferograms, considering the likelihood of movements, their distance to rivers and faults, as well as estimated volume and velocity per year. The results indicate that a total of 29.6 % of all features constitute a high damming hazard potential in case of catastrophic failure, with 4.5 % located within 1 km of the Rogun Dam reservoir. Although many potential sites are not directly on the slopes rising above the future reservoir, hazardous locations in the catchment upstream pose a threat due to possibility of significant outburst floods in case of the dammed lake outburst.
Contrasting spatial distributions of surface sediment compositions from the Emperor Seamount Chain, North Pacific
Authors: Chen Jie , Zou Jianjun , Shi Xuefa , Lembke-Jene Lester , Nürnberg Dirk , Tiedemann Ralf
Published: March 2020

The Emperor Seamount chain is located in the North Pacific Ocean and beneath the Northern Westerly wind belt. It extends from the subtropical to subarctic North Pacific oceans between 30°N-50°N. Modern observations have shown this region has complex physical oceanic processes, including the Kuroshio Extension, the Oyashio Current, the polar front and the subarctic front. A large amount of dust from the central Asian continent is delivered to this area, which affects the regional marine ecosystem and the global carbon cycle. Due to the lack of sediments from the Emperor Seamount chain, few studies have examined the composition of surface sediments in this ocean realm. On the basis of 50 samples collected during the SO264 Expedition in 2018 using multicorers, we investigate the spatial distributions of sediment grainsize, total organic carbon, CaCO3 and major and minor elements in surface sediments of this ocean realm. Our data show that the detritus sediments mainly consist of siltly sand and clayey silt with more coarse fractions between ~45°N and 48°N, which has strong negative correlations with water depth. The content of CaCO3 varies between 0.04% and 83.67% with higher values at the south of 48°N. The TOC content ranges between 0.07% and 1.36% with lower values (<0.3%) occurring at the north of ~45°N. The concentration of ∑REEs ranges from 31 ppm to 136 ppm with lower values between ~45° N and 48°N. There is significant positive Eu anomaly at all stations, indicating widespread occurrence of volcanic detritus. A significant negative correlation between sediment grainsize and ∑REEs and some lithophile elements, such as Al2O3, Fe2O3, K2O, Th, REEs, etc., indicates a strong effect of sediment grainsize on sediment geochemical composition. A strong negative correlation between Al and CaCO3 suggests contrasting sources, such as terrigenous vs biogenic sources, respectively. Our data confirms the contributions of terrigenous, volcanic and biogenic materials to the bulk sediment with contrasting spatial distribution along the Emperor Seamount Chain.

Note: This study was supported by the National Natural Science Foundation of China (Grant No.41876065, U1606401) and National Program on Global Change and Air-Sea Interaction(GASI-GEOGE-04). 
Neotectonics and landscape characterization in the Gawler Craton, South Australia - Insights through high-resolution remote sensing
Authors: Martinez Cericia , Kelka Ulrich , Gonzalez-Alvarez Ignacio , Krapf Carmen
Published: March 2020

The Gawler Craton hosts significant economic mineralization within South Australia. Due to limited outcrops, deeply weathered profiles, and the absence of a clear variety of landscape surface features, mineral exploration is particularly challenging in this part of Australia. Here we present a workflow of data processing and interpretation to understand the neotectonics and landscape characterization of this region. We explore the potential to delineate surface lineaments and features from newly acquired high-resolution datasets. We aim to automatically identify landform domains based on the analysed data and investigate whether deep seated tectonic lineaments manifest in recognizable surface expressions.

The data we analyse in this study comprises digital elevation, radiometric, magnetic, and gravity data. We assume that elevation and radiometric data relate to surficial landscape features, whereas gravity and magnetic data represent subsurface basement features. Linking the analysis of both surface and subsurface datasets can potentially yield information on the neotectonic activity, and the association between landforms and basement structures as potential zones of fluid migration. We will show how processed digital elevation data can be used for automatic classification of different landform domains.

In order to assess mineral potential zones in the area, we compare the generated lineament data in terms of their geometric and topological properties to examine whether there is consistency in the subsurface and surface layers. We postulate that through a line density map, we may be able to quantify a potential relationship between lineaments that are representative in both the surface and subsurface, indicating potential faults or large-scale lineament trends that may link mineral systems in the basement with the landscape surface features. Areas that exhibit large numbers of surface and subsurface lineaments might be areas of enhanced mineral potential. This study contributes to enhance the efficiency of mineral exploration protocols in areas under cover.
Using seismic networks and satellite radars to detect landslide events
Authors: Manconi Andrea , Mondini Alessandro ,   AlpArray Working Group
Published: March 2020

Catalogues are the base to study the causes leading to slope failures and to define landslide hazard and early warning strategies at regional scales. Despite recent efforts, the knowledge on spatial and temporal landslide distribution is often very poor. Information on timing, location, magnitude and landslide dynamics, is generally available only when the events threat life or damage infrastructures, as well as when they are associated with catastrophic earthquakes or exceptional meteorological occurrences. Moreover, many landslide events are unreported because they occur in remote regions and thus do not have immediate impacts on human activities. This may strongly hinder the completeness of landslide catalogues, and thus the subsequent interpretation in terms of hazard assessment. Complete catalogues are crucial to study the relationships between local and regional landslide preconditioning factors, to recognize potential triggers, as well as to clearly identify the effect of climate forcing. In recent years two procedures are dominating the panorama of landslide event detection, i.e. remote sensing approaches and seismic data analyses. This is mainly due to the increased availability of such data at global scale, as well as to the applied open access data policies. Here we present a procedure to detect landslide events by jointly analyzing data acquired from regional broadband seismic networks and spaceborne radar imagery. As an exemplary case, we consider a series of events associated to the recent Piz Cengalo rock slope failure occurred on August, 2017 in the Swiss Alps, a region where we can now benefit from the high spatial density of the AlpArray seismic network and from the spatial and temporal resolution of Sentinel-1 radar imagery. The operational implementation of the herein proposed approach, in combination with the expected increase in availability of seismic and satellite data, can provide a new and efficient solution to build and/or expand landslide catalogues based on quantitative and homogeneous measurements, as well as to integrate landslide early warning systems at regional scales.
Understanding Harmful Algal Bloom Dynamics in a Mediterranean Hypereutrophic Reservoir insights from a Bayesian Network and a Structural Equation Model
Authors: Alameddine Ibrahim , Deutsch Eliza
Published: March 2020

Cyanobacteria blooms, especially those involving Microcystis, are an increasing problem facing many freshwater systems worldwide. In this study, a Bayesian Network (BN) along with a Structural Equation Model (SEM) were concurrently developed through data-driven learning and expert elicitation in order to better delineate the main pathways responsible for the Microcystis dominance in a Mediterranean semi-arid hypereutrophic reservoir. The resulting two model structures were then compared with regards to the pathways they identified between the physical lake conditions and the nutrient loads on one hand and Microcystis dominance on the other. The two models were also used to predict the probability of bloom formation under different scenarios of climate change and nutrient loading. Both models showed that, given the eutrophic status of the study reservoir, direct temperature effects appear to be the primary driving force behind the Microcystis growth and dominance. Indirect temperature effects, which modulated water column stratification and internal nutrient release, were also found to play an important role in bloom formation. On the other hand, both models revealed that the direct nutrient pathways were less important as compared to the temperature effects, with internal nutrient loads dominating over external loads due to the seasonal variability in river flows, typical of Mediterranean rivers. Nevertheless, the BN model was unable to capture the recursive relationships between Microcystis and its forcings.
Small scale transport processes from HF-Radar
Authors: Hernández-Carrasco Ismael , Orfila Alejandro , Rossi Vincent , Garçon Veronique
Published: March 2020

Coastal ocean ecosystems are major contributor to the global biogeochemical cycles and biological productivity. Physical
factors induced by the turbulent flow play a crucial role in regulating marine ecosystem. However, while large scale dynamics
in the open ocean is well described by geostrophy, the role of small scale transport processes in coastal regions is still
poorly understood due to lack of continuous high-resolution observations. Here, the influence of small-scale coastal dynamics
on surface phytoplankton structuring is studied using Lagrangian metrics computed from HF Radar currents and satellite
chlorophyll-a (Chl). The combination of complementary Lagrangian diagnostics, including the accumulated divergence of the
flow along fluid trajectories, provides an improved description of the 3D flow geometry which facilitates the interpretation of two
non-exclusive physical mechanisms affecting phytoplankton patchiness. Attracting submesoscale fronts, unveiled by backwards
Lagrangian Coherent Structures, are associated to negative Lagrangian divergence where particles and Chl standing stocks
cluster. Filaments of positive Lagrangian divergence, representing large accumulated upward vertical velocities and suggesting
accrued injection of subsurface nutrients, match areas with large Chl concentrations. Our findings demonstrate that an accurate
description of small-scale transport processes is necessary to comprehend bio-physical interactions in coastal seas and to
estimate biological productivity.
Socio-hydrological modelling: the influence of reservoir management and societal responses on flood impacts
Authors: Albertini Cinzia , Mazzoleni Maurizio , Totaro Vincenzo , Iacobellis Vito , Di Baldassarre Giuliano
Published: March 2020

Over the last few years, several socio-hydrological studies have investigated the dynamics of risk generated by feedback mechanisms and interactions between floods and societies, with a focus on either changing reservoir operation rules or raising levees. In this study, we propose a new socio-hydrological model of human-flood interactions that represents both changes in the operating rules of reservoirs and updating of the levee system. Our model is applied to simulate three prototypes of floodplain management strategies: green systems, in which societies cope with flood risk by resettling outside the flood-prone area; technological systems, in which societies cope with flood risk also via structural measures, such as levees; and green-to-techno systems, in which societies shift from green to technological approaches. Floodplain dynamics are explored simulating future scenarios in the city of Brisbane, Australia. Results show that flood risk is strongly influenced by the flood memory of reservoir operators and their risk-awareness levels control the development of communities. Furthermore, scenarios of more frequent and higher magnitude events prove to enhance social preparedness levels in green systems, while technological systems experience much higher losses.
On the Dependence of Cirrus Parametrizations on the Cloud Origin
Authors: Kuhn Thomas , Wolf Veronika , Krämer Martina
Published: March 2020

Particle size distributions (PSDs) for cirrus clouds are important for both climate models as well as many remote sensing retrieval methods. Therefore, PSD parametrizations are required. This study presents parametrizations of Arctic cirrus PSDs. The dataset used for this purpose originates from balloon-borne measurements carried out during winter above Kiruna (Sweden), i.e. north of the Arctic circle. The observations are sorted into two types of cirrus cloud origin, either in-situ or liquid. The cloud origin describes the formation pathway of the ice particles. At temperatures below −38 °C, ice particles form in-situ from solution or ice nucleating-aerosol particles. Liquid origin ice particles have formed at temperatures warmer than or equal to −38 °C, either via ice-nucleating particles embedded in liquid drops or via homogeneous drop freezing, and are then further uplifted to the cirrus temperature regime.

In order to derive parametrizations for each cloud origin, the observed PSDs are represented by gamma functions. The gamma coefficients exhibit large differences with regard to cloud origin. Functions describing the relationships in between the gamma coefficients and with temperature are fitted. These functions for Arctic cirrus confirm established parametrizations for continental cirrus sorted by two particle size modes but differ from others depending only on temperature. We suppose that the agreement between the parametrizations of the geographically different cirrus is because in-situ and liquid origin cirrus also distinguish by particle size modes. Since cloud sorting by their origin is based on physical processes that are independent of geographical region, we further hypothesize that these cloud-type-based parametrizations might be generally valid for use in global models and satellite retrievals, given the distribution of the cloud types is known.
Climate-driven phytoplankton community shifts in the North Pacific Subtropical Gyre
Authors: Yoon Joo-Eun , Kim Il-Nam
Published: March 2020

Natural climate variability influences phytoplankton community both directly and indirectly by altering ocean stratification and availabilities of nutrient and light, or grazing pressure. The world’s largest ecosystem, North Pacific Subtropical Gyre (NPSG), is largely controlled by basin-scale decadal climate variability, such as the North Pacific Gyre Oscillation and the Pacific Decadal Oscillation. These indices have two phases, known as warm phase and cool phase, respectively. Previous studies reported that warm phase was related to the dominance of pico-phytoplankton induced by warm temperature anomaly (i.e., strong stratification) while cool phase was related to the dominance of nano-phytoplankton induced by cold temperature anomaly (i.e., weak stratification). Besides the impact of natural climate variability, anthropogenic global warming has accelerated in recent years and it might have abnormal impact on marine ecosystems. However, there is little information about the responses of phytoplankton community to recent climate change in the NPSG. Here, we present the temporal variations of deseasonalized and normalized NPSG phytoplankton community using phytoplankton pigment concentrations and cell densities, obtained on monthly intervals over the period 1988−2018 at Station ALOHA (22°45’N, 158°W). These variations were compared with the variations of climate indices, physical, and biogeochemical parameters from Station ALOHA. The NPSG climate indices showed five phase transitions; warm (~1997) – cool (1998−2002) – warm (2003−2006) – cool (2007−2013) – warm (2014~). Before 2006 year, the phase transitions of phytoplankton community (pico→nano→pico) were coincident with physical factors (e.g., stratification; strong→weak→strong) and biogeochemical factors (e.g., particle export; low→high→low), coupling with phases of climate indices. However, interestingly, following the recent rapid rise in greenhouse gas emission (since 2007), phytoplankton community, even under continued coupling of climate indices and physical factors, showed only dominance of pico-phytoplankton, decoupling with the phases of climate indices. These findings suggest that the contribution of pico-sized plankton to NPSG phytoplankton community will increase gradually in response to the acceleration of the global warming.
Combining isotopic and sap flux data to estimate GPP: an alternative ecophysiological approach to eddy-covariance based data
Authors: Vernay Antoine , Tian Xianglin , Lopez Jose , Hasselquist Niles , Mäkelä Annikki , Oren Ram , Tor-ngern Pantana , Stangl Zsofia R , Marshall John D
Published: March 2020

Stand-scale estimates of gross primary production (GPP) commonly depend on eddy-covariance or eddy-covariance derived models. Chamber-based methods provide an alternative, but they are tricky to scale up to the stand. We estimate GPP by combining isotopic δ13C of phloem sugars with sap-flow measurements. The method consists of calculating intrinsic water-use efficiency and transpiration to determine GPP. We have improved this approach by considering mesophyll conductance and seasonal variation in photosynthetic capacity and then compared our results to a semi-empirical eddy-covariance based model, PRELES. We compared a fertilised plot and an unfertilised plot in a monospecific Scots pine forest in northern Sweden. The method captured both the stand response to fertilisation and seasonal patterns, as PRELES did. Our results demonstrate the importance of considering a finite mesophyll conductance value to avoid an unreasonable overestimate of GPP. We have now applied the method in a mixed boreal forest where we will partition total stand GPP among the three dominant tree species (pine, spruce, and birch). This approach provides an independent test of GPP estimates and provides a means of estimating GPP where eddy-covariance assumptions are not met.
Predictability of large subduction earthquakes: insights from analog models and machine learning
Authors: Corbi Fabio , Bedford Jonathan , Sandri Laura , Funiciello Francesca , Gualandi Adriano , Rosenau Matthias
Published: March 2020

Despite the growing spatio-temporal density of geophysical observations, our understanding of the megathrust earthquake cycle continues to be limited by a series of factors, in particular the short observation time compared to mega-earthquake recurrence and the partial spatial coverage of geodetic data. Here, we attempt to compensate for these natural limitations by simulating dozens of seismic cycles in a laboratory-scale analogue model of subduction. The model creates analog earthquakes of magnitude Mw 6.2–8.3, with a coefficient of variation in recurrence intervals of 0.5, similar to real subduction megathrusts. Using a digital image correlation technique, we measure coseismic and interseismic deformation – this is akin to having a dense continuous geodetic network homogeneously distributed over the whole margin. We show how, by deciphering the spatially and temporally complex surface deformation history, machine learning can predict the timing and size of analog earthquakes. Then, we investigate data characteristics that maximize the performance of a machine learning binary classifier predicting slip-events imminence. We show how this framing can be used for designing an efficient geodetic network, and defining the minimum space-time coverage requirements for analog earthquake prediction. Converting the laboratory scale to the natural scale, we found that a 70-85 km wide coastal swath gives the most important information on slip imminence and that model performance is mainly  influenced by the alarm duration, with density of stations and record length playing a secondary role. Under optimal monitoring conditions, about ten seismic cycles long record is enough to predict alarm periods in good agreement with those observed.
Quantifying the Pyrocene: How Important is Fire to Life on Earth?
Authors: Belcher Claire
Published: March 2020

Fire and vegetation have a dual interaction with each other, whilst also both influencing the environment and atmosphere. For example, fire regimes are themselves controlled by atmospheric conditions, atmospheric composition, climate and the type of vegetation. Whilst, the effects of fires, the products and emissions they generate influence biogeochemical cycles and long-term Earth system processes through their impacts on nutrient cycles and by altering the composition and distribution of biomes. Hence fire is more than a simple agent of disturbance and has a multitude of complex feedbacks.

Wildfires have shaped our ecosystems and Earth system processes for some 420 million years. For example the presence of and changes in fire frequency and behaviour on evolutionary timescales has influenced the physiological traits of plants such that many ecologists have interpreted them as adaptations to fire. For example, serotiny in the Pine lineage is believed to have evolved millions of years ago in the Late Cretaceous period, where wildfires were both frequent and intense. Such traits seemingly continue to allow some plants to succeed in fire prone areas. However, humans have entirely altered ignition patterns, with some 95% of fires being started by man; we have altered the connectivity of fuels in landscapes, species composition and fuel structure. Yet we have limited understanding to what extent we have disrupted fire feedbacks to the Earth system. This lies in large part because we have not yet well understood what natural feedbacks fire has had on our planet throughout its history.

In this talk I will explore some of the critical history of fire and some of the processes that fire appears to regulate in order to pose the question - are fires a critical resource that secures the long-term balance of the Earth system that keeps our planet habitable to man?
A space-based perspective on cloud phase partitioning over the Southern Ocean
Authors: Coopman Quentin , Hoose Corinna , Stengel Martin
Published: March 2020

Liquid cloud droplets freeze homogeneously at -40°C. For temperature between -40 and 0°C, clouds can be either liquid, ice, or mixed-phase. Several variables determine the cloud phase: droplet size, ice nuclei concentration, meteorological parameters, etc. But, parameters which trigger, enhance or inhibit the phase transition are still poorly understood and disagreements remain between theory and observations. The phase transition is nonetheless important to determine cloud effects on climate.

In the present study, we analyse satellite observations from the geostationary passive instrument SEVIRI. We used the CLAAS-2 dataset to retrieve cloud top microphysical and optical properties from 2005 to 2015 over the Southern Ocean.

Cloud objects that contain liquid and ice pixels are identified for cloud top temperatures within specific temperature ranges: between -30 and -20°C, between -20 and -8°C, and between -8 to 0°C. The distributions of different cloud properties for mixed-phase, liquid or ice clouds are compared. For example, preliminary results show that cloud ice fraction increases with the cloud droplet size for cloud top temperature between -8 and 0°C. Indeed, ice fractions greater than 0.8 are associated with a median cloud droplet effective radius of 7 micrometers whereas ice fractions less than 0.2 are associated with a median cloud droplet effective radius of 12 micrometers. We hypothesize that this result can be associated to a secondary ice production process (e.g., the Hallet-Mossop process is the splinter production associated with riming process for temperature between -8 and -3°C and it can increase the ice particle concentration by several orders of magnitude). In line with our results, the Hallet-Mossop process is more efficient with larger cloud droplets. The spatial distribution of liquid and ice pixels within the cloud objects is also studied to better understand the phase partitioning of mixed-phase clouds.