bluuebunny/crossref_metadata_2025 huggingface dataset:
Climate Services for eXtremes: Bi-directional knowledge transfer for developing adaptation strategies in agriculture and forestry on the example of the 2018-2020 summer drought in Germany.
Authors: Haustein Karsten , Rechid Diana , Knutzen Florian , Groth Markus , Averbeck Paul , Froer Oliver , Hey Lukas , Jungkunst Hermann
Published: March 2021

The main goal of Climate Services for eXtremes (which in is an integral part of the ClimXtreme framework) is to advance our understanding of the intensity as well as the spatio-temporal distribution of extreme weather and climate events, but tailored to the needs of stakeholders in the agricultural and forestry sector. The project is designed to optimise the communication between scientists and decision makers and thus to maximise the mutual benefit with regard to climate adaption. The scientists involved learn from the interview partners what climate information is actually required on the ground to facilitate the development of adaptation strategies, whereas the sector experts gain insights into the capabilities and limits of state-of-the-art climate information.

In order to increase the efficiency of the knowledge transfer between scientists and stakeholders, we introduce a process-chain based approach: (i) the sector-specific identification of the characteristics of extreme weather conditions in close cooperation with partners from forestry and agriculture, (ii) the analysis of past and future weather and climate extremes with various statistical techniques, (iii) the investigation of the effects of these extremes by means of forest and agricultural case studies, and (iv) the development of possible needs-based adaptation strategies to future climatic conditions and extreme events based on this information.

The extended summer drought in Germany during the warm seasons 2018 to 2020 is the perfect testbed for the approach, given the wide-ranging consequences this multi-year event had especially on the forestry sector. The event will be analysed from a probabilistic point of view, i.e. what is the return time and what were the causal factors from an atmospheric dynamic and teleconnection point of view. There is also potential to investigate the role of climate change in terms of altered risks. With this information, we can offer initial guidance for the project partners as to what they have to prepare for. But crucially, the interview feedback will help guide our ultimate research strategy. It will be a function of spatial scale, indices of interest as well as scope and complexity of the data and services our partners require. The new insights will serve as a basis to investigate such extreme drought events under potential future climate conditions. 
Pathways connecting the North Brazil Current and the RAPID line
Authors: Drouin Kimberley , Lozier M Susan , Beron-Vera F Javier , Miron Phillip , Olascoaga M Josefina
Published: March 2021

The North Brazil Current is considered a bottleneck in the South Atlantic, responsible for funneling upper-ocean waters into the North Atlantic. This work explores the surface and subsurface pathways that connect the North Brazil Current to the RAPID line. To that extent, observational trajectories from surface drifters and Argo floats are used in conjunction with Markov chain theory and tools from dynamical systems analysis to compute probable pathways. More specifically, these pathways are computed as ensembles of paths transitioning directly between the North Brazil Current and the RAPID line. In addition, simulated trajectories will be used (1) to assess how representative the two-dimensional observational trajectories are of the three-dimensional circulation, and (2) to compute the associated volume transport of different pathways. Preliminary results suggest that two dominant pathways connect the North Brazil Current and the RAPID line. First, is the traditional pathway through the Caribbean Sea and Gulf of Mexico, which carries waters to the Florida Current, and second is a more direct route east of the Caribbean that supplies waters to the Antilles Current and the basin interior.  
The resistivity structure of the Hekla volcano in South Iceland: first insights from electromagnetic investigations
Authors: Kiyan Duygu , Benediktsdóttir Ásdís , Hersir Gylfi P. , Guðmundsson Magnús T. , Bean Christopher J. , Hogg Colin , Jonsson Steini , Einar Jónsson Jón
Published: March 2021

Hekla is one of Iceland’s most active volcanoes having had 18 summit eruptions in the last 1,100 years with the most recent eruption in 2000. Hekla volcano has been studied extensively using various geodetic methods. Most recent deformation studies (InSAR) in relation to the 2000 eruption of Hekla have addressed the proposed location of a deep-seated magma reservoir at approximately 10 km (Sturkell et al., 2013) where other studies indicate a greater depth (Ofeigsson et al., 2011). A regional-scale magnetotelluric (MT) survey (Eysteinsson and Hermance 1985) conducted in 1982 suggested the estimated depths for the magma chamber beneath the volcano to be between 5 and 24 km. Our new project MTHEK (MagnetoTelluric Assessment of the HEKla Volcano) aims at identifying low-resistivity zones at depth, which may be a proxy for melt accumulation and migration pathways, and may constrain the location of the proposed magma reservoir. The geoelectrical models obtained will enable us to highlight potential real-time electromagnetic monitoring locations which may complement the current real-time seismic/deformation monitoring.

In September 2020, broadband MT data were acquired at 20 stations around and to the south of Hekla volcano. The horizontal electric field components were recorded using 50-60 m dipoles, and the three components of the magnetic field were measured using induction coils. At most stations, the recording time was approximately 20 hours, and a distant remote reference site (approximately 100 km away) was recording during the whole survey. The period range of good quality data obtained is about 300 Hz to 1,000 - 2,000 s. In addition, at 17 MT stations central loop transient electromagnetic (TEM) data were collected using a transmitter loop of 200 m × 200 m and a 1 m2 receiver loop with 100 windings (effective area 100 m2). The TEM data are used to correct the MT data for static shift effects caused by near surface inhomogeneities or steep topography. State of the art data processing and analysis methods are being applied to the data. Preliminary inversion models will be presented and provide a first idea of the resistivity structure of the volcano.
Rapid mapping of landslides by Deep-Learning of combined optical and SAR data
Authors: Nava Lorenzo , Catani Filippo , Monserrat Oriol
Published: March 2021

In the world, various natural calamities, like earthquakes and massive rainfalls sometimes combined with windstorms, can trigger multiple landslide events that can occur in groups of hundreds to thousands in a region, over a short time span. Therefore, there is a growing need to be able to intervene quickly to accurately map the impacted areas. To this end, VHR optical images ensure best performances in terms of spatial accuracy but, for rapid mapping, they present limitations due to the possible presence of cloud cover as, often, the first cloudless image is available with an unacceptable time delay, see, e.g., the cases of strong earthquakes of Chile 2017, Nepal 2015 and Ecuador 2016. A possible solution may stand in the combined exploitation of optical and SAR data. In this study, deep-learning convolution neural networks (CNNs) techniques have been used to compare and combine the mapping and classification performances of optical images (from Sentinel-2) and SAR images (from Sentinel-1). The training and test zones used to independently evaluate the performance of CNNs on different datasets are located in the eastern Iburi subprefecture in Hokkaido, where, at 03.08 local time (JST) on September 6, 2018, a Mw 6.6 earthquake triggered about 7837 coseismic landslides. We analyzed the conditions before and after the earthquake exploiting SAR and optical data by means of a series of CNNs implemented in Python that point out the locations where the Landslide class is predicted as more likely. As expected, the CNN run on optical images proved itself excellent for the landslide detection task, achieving an overall accuracy of 98.48% while a CNN based on the combination of ground range detected (GRD) data (SAR) achieved an overall accuracy of 95.54%. Despite this, the integrated use of SAR data allows for a rapid mapping even during storms and under cloud cover and seems to provide a comparable accuracy than optical change detection. We believe that, in the near future, such classification accuracy might even increase with the availability of new, VHR SAR products, such as the 50 cm x 50 cm resolution imagery from the Capella-2 satellite.
Hydrological modelling and anthropogenic water use
Authors: Rameshwaran Ponnambalam , Rudd Ali , Bell Vicky , Brown Matt , Davies Helen , Kay Alison , Sefton Catherine
Published: March 2021

Despite Britain’s often-rainy maritime climate, anthropogenic water demands have a significant impact on river flows, particularly during dry summers. In future years, projected population growth and climate change are likely to increase the demand for water and lead to greater pressures on available freshwater resources.

Across England, abstraction (from groundwater, surface water or tidal sources) and discharge data along with ‘Hands off Flow’ conditions are available for thousands of individual locations; each with a licence for use, an amount, an indication of when abstraction can take place, and the actual amount of water abstracted (generally less than the licence amount). Here we demonstrate how these data can be used in combination to incorporate anthropogenic artificial influences into a grid-based hydrological model. Model simulations of both high and low river flows are generally improved when abstractions and discharges are included, though for some catchments model performance decreases. The new approach provides a methodological baseline for further work investigating the impact of anthropogenic water use and projected climate change on future river flows.
The Two-order risk framework: A spatial assessment of risks associated with Covid-19 in the European Union (EU) 
Authors: Schütze Simon , Hassel Jonathan
Published: March 2021

The fast spread of SARS-CoV-2 made non-pharmaceutical interventions, such as the closure of schools and national lockdowns, necessary. These containment measures are essential to protect the health and safety of the people, while simultaneously posing a potential threat to the functioning of other aspects of society e.g., the economy, social life, or physical and mental health.  

The connection of the risks directly imposed by the hazard (in this case a pandemic) and the indirect risks imposed by coping and adaptation measures is not well captured by existing multi/risk frameworks. Additional to the emerging multi-risk frameworks around concepts of cascading, conjoint or compounded risk, a framework is needed that focusses on the socially constructed risk as a direct response to the risk of the natural hazard itself. Building on the first- and second-order of adaptation concept by Birkmann (2011), this paper develops the “Two-order risk framework” for structurally assessing both interconnected risks. This framework can be applied for indicator-based spatial risk analysis of numerous types of disasters that are accompanied by prolonged coping or adaptation phases.  

Here, the framework is employed to quantify the risk of COVID-19 for all EU member states. It conceptualises the risk of immediate impacts due to SARS-CoV-2 (first-order risk) as well as the risk of impacts of containment (second-order risk) measures by assessing the hazard/exposure, vulnerability and coping capacity in each order of risk. Both orders of risk are affected and connected by the specific risk management capacities of a country. Higher risk management capacity can decrease the threat of SARS-CoV-2, while poor risk management capacity can increase the threat of harmful containment measures. For assessing risk management capacity, governance-related indicators play a central role. The findings reveal that Malta, Luxemburg, and Denmark have a significantly lower second-order risk than first-order risk. The opposite is true for Latvia, Poland and Ireland. For the goal of reducing the overall risk, the policy advice given to states with a high first-order risk must be substantially different than the one given to those with a higher second-order risk.  

The spatial heterogeneity of vulnerabilities in both risks shows that a one-size-fits-all approach in regards to containment measures is not sufficient to minimize risk in the EU. Instead, containment measures need to address country-specific drivers of the disease-spread while considering the vulnerability to second-order risk.    
Spatio-temporal clustering methodologies for point-event natural hazards
Authors: Zandovskis Uldis , Malamud Bruce D. , Pigoli Davide
Published: March 2021

Natural hazards are inherently spatio-temporal processes. Spatio-temporal clustering methodologies applied to natural hazard data can help distinguish clustering patterns that would not only identify point-event dense regions and time periods, but also provide insight into the hazardous process. Here we review spatio-temporal clustering methodologies applicable to point event datasets representative of natural hazards and we evaluate their performance using both synthetic and real life data. We first present a systematic overview of major spatio-temporal clustering methodologies used in the literature, which include clustering procedures  that are (i) global (providing a single quantitative measure of the degree of clustering in the dataset) and (ii) local (i.e. assigning individual point events to a cluster). A total of seven methodologies from these two groups of clustering procedures are applied to real-world (lightning) and synthetic datasets. For (i) global procedures, we explore Knox, Mantel, Jacquez k-NN tests and spatio-temporal K-functions and for (ii) local procedures we consider spatio-temporal scan statistic, kernel density estimation and density-based clustering method OPTICS. The dataset of 7021 lightning strikes is from 1 and 2 July 2015 over the UK, when a severe three-storm system crossed the region with different convective modes producing each of the storms. The synthetic datasets are representative of various topologies of a point-event natural hazard data with a moving source. We introduce a two-source model with input parameters related to the physical properties of the source. Each source has a set number of points events, initiation point in space and time, movement speed, direction, inter-event time distribution and spatial spread distribution. In addition to a base model of two identical moving sources with a set temporal separation, we produce four different topologies of the data by incrementally varying the speed parameter of the source, spatial spread parameters, direction and initiation points, and angle of two sources. With these five synthetic datasets representative of various two-source models, we evaluate the performance of the methodologies. The performance is assessed based on the ability of each methodology to separate the point events produced by the two sources and the sensitivity of these results to changes in the model input parameters. We further discuss the benefits of combining global and local clustering procedures in the analyses as we gain an initial understanding of the spatial and temporal scales over which clustering is present in the data by using global clustering procedures. This information then helps to inform and limit the choice of input parameters for the local clustering procedures.
Process-based model estimation of N2O Emission factors for urine patches in a Swiss grazing system 
Authors: Kuntu-Blankson Kate , Six Johan , Barczyk Lena , Ammann Christof , Calanca Pierluigi
Published: March 2021

Nitrous oxide (N2O) is a powerful greenhouse gas (GHG) with a global warming potential about 300 times that of carbon dioxide (CO2). In Switzerland, N2O emissions contribute to about 6% of the total GHG emissions, agriculture being responsible for more than 60% of the former. Understanding the processes driving N2O emissions from agricultural land is therefore of paramount importance for developing national GHG emissions inventories. Of relevance in this respect is the fact that about two-thirds of the agricultural lands are grasslands, part of which are managed as pastures.

Urine deposited by grazing animals has high N loads and induce increased nitrification and denitrification. Urine patches are hence hotspots for N2O emissions. In the IPCC Tier 1 method still in use in Switzerland for quantifying N2O emissions, a default EF3 value of 2% is assumed for excreta (dung and urine). This does not properly account for the spatial heterogeneity of N returns from grazing animals. Recent studies have indeed shown that country-specific EF3 are typically much lower than the default IPCC value. These results suggest that the use of IPCC Tier 2 and Tier 3 methods, that rely on the application of process-based models, is to be preferred for estimating countrywide N2O emissions.

In this work, we will apply the comprehensive process-based model ecosys to simulate N2O emissions from urine patches in a Swiss grazing system. We report on preliminary results from experiments aiming at modelling artificially applied urine patches. After showing that the model is able to reproduce the emission rates measured in a companion field trial, we use ecosys to examine N fractions lost to direct (N2O emissions) and indirect (ammonia volatilization, nitrate leaching and runoff) pathways for urine-N input rates varying from 500-2000 kg N ha-1. We also apply the model to understand the effects of seasonal variations in the environmental drivers on N2O EF. This work is part of a PhD conducted by the first author that aims at developing the scientific basis for establishing country-specific EFs for grazing-related N2O emissions in Switzerland.
Assessing drought-induced mortality of European beech and Scots pine in the Valais, Switzerland
Authors: Rothenbühler Sabine , Walthert Lorenz , Saurer Matthias , Gärtner Holger , Gessler Arthur , Rigling Andreas , Tinner Willy , Tenzin Karma , Treydte Kerstin
Published: March 2021

Tree mortality due to climate change and particularly drought is a globally observed issue and has been studied widely. However, the underlying physiological mechanisms are still not fully understood. One approach to assess the drivers of drought-induced mortality is to retrospectively investigate predisposing factors that have led to tree death by utilizing tree rings. Here we combine annual stem growth, and stable carbon and oxygen isotopes (𝛿13C and 𝛿18O) in tree rings of recently died and living trees of two species, drought tolerant Pinus sylvestris and drought sensitive Fagus sylvatica, in the Rhone Valley (Valais), the driest part of Switzerland.

Irrespective of specific drought tolerance, growth patterns of now-dead and living trees were significantly different in both species. Now-dead trees showed higher growth rates than living trees, for at least half of their life span. In the last two decades this pattern was reversed and growth of now-dead trees was at a lower level compared to living trees. In this recent time period, 𝛿18O records of now-dead trees of both species showed a distinct decrease, while no systematic difference was found in the tree-ring 𝛿13C records of now-dead and living trees. Climate correlation analysis revealed that stem growth of now-dead trees was more sensitive to climate compared to living trees and that the relationship between isotope-derived leaf gas exchange and climate weakened in the late period prior to death.

Our findings suggest that now-dead trees followed a more conservative water-use strategy in their declining phase. Decreasing  values and weakened relationships to climate indicate a reduction in stomatal conductance, accompanied by reduced photosynthetic activity, since the ratio of photosynthesis to stomatal conductance remained unchanged. Overall, our results suggest a combination of hydraulic failure and carbon starvation as initiators of tree death at our study sites, probably in different stages of tree life. It is obvious that recent climate conditions already strongly affected the trees, such that in a future environment negative effects will most likely increase.
A snowfall downscaling scheme for mountainous terrain
Authors: Helbig Nora , Mott Rebecca , Bühler Yves , Lehning Michael , Bartelt Perry
Published: March 2021

In mountainous terrain, the spatial and temporal variability of the snow cover is driven by the interaction of meteorological processes with the underlying topography. Typically, terrain-precipitation-wind interactions predominantly shape the spatial snow depth distribution during the accumulation season through drifting snow and preferential deposition of snowfall. While a suspension model forced with fine-scale three-dimensional wind fields can generate spatial preferential deposition patterns, fine-scale three-dimensional wind fields or the necessary computational demands cannot be met by most model applications over larger areas.

We present an efficient statistical snowfall downscaling scheme over complex topography reproducing preferred fine-scale snowfall deposition patterns. Towards this we generated several thousands of spatial new snow distributions on artificial topographies by modeling preferential deposition with a suspension model and pre-computed Advanced Regional Prediction System (ARPS) wind fields. To systematically analyze spatial preferential deposition patterns, we chose artificial topographies covering a broad range of real terrain characteristics as well as controlled conditions for the model runs. We developed two statistical downscaling schemes using several millions of distributed fine-scale snowfall values. With one parameterization, we scale coarse-scale snowfall with fine-scale surface vertical wind components and topographic parameters. If fine-scale vertical wind components are not available, a second parameterization can be used to scale coarse-scale snowfall with coarse-scale wind direction and fine-scale topographic parameters. The spatial patterns of preferential snowfall deposition were well reproduced by the parameterizations, indicating that the downscaling scheme can be used for various model applications such as hydrological, avalanche, weather, and climate forecasts or hazard mapping.
The impact of COVID-19 on CO2 emissions in the Los Angeles and Washington DC/Baltimore metropolitan areas 
Authors: Karion Anna , Yadav Vineet , Ghosh Subhomoy , Mueller Kimberly , Roest Geoffrey , Gourdji Sharon , Lopez-Coto Israel , Gurney Kevin , Parazoo Nicholas , Verhulst Kristal , Kim Jooil , Prinzivalli Steve , Fain Clayton , Nehrkorn Thomas , Mountain Marikate , Keeling Ralph , Weiss Ray , Duren Riley , Miller Charles , Whetstone James
Published: March 2021

Responses to COVID-19 have resulted in unintended reductions of city-scale carbon dioxide (CO2) emissions. Here we detect and estimate decreases in CO2 emissions in Los Angeles and Washington DC/Baltimore during March and April 2020. Our analysis uses three lines of evidence with increasing model dependency. The first detects the timing of emissions declines using the variability in atmospheric CO2 observations, the second assesses the continuation of reduced emissions using CO2 enhancements, and the third employs an inverse model to estimate the relative emissions changes in 2020 compared to 2018 and 2019. Emissions declines began in mid-March in both cities. The March decrease (25%) in Washington DC/Baltimore is largely supported by a drop in natural gas consumption associated with a warm spring whereas the decrease in April (33%) correlates with changes in gasoline fuel sales, a proxy for vehicular emissions. In contrast, only a fraction of the March (17%) and April (34%) reduction in Los Angeles is explained by traffic declines, while the remainder of the emissions reduction remains unexplained. To help diagnose such observed changes in emissions, more reliable, publicly available emission information from all significant sectors needs to be made available. Methods and measurements used herein highlight the advantages of atmospheric CO2 observations for providing timely insights into rapidly changing urban emissions patterns that can empower cities to course-correct mitigation activities more efficiently.
Commercial microwave links as rainfall input data in urban hydrological modelling
Authors: Cazzaniga Greta , De Michele Carlo , Deidda Cristina , D'Amico Michele , Ghezzi Antonio , Nebuloni Roberto
Published: March 2021

Many studies in literature have showed that hydrological models are highly sensitive to spatial variability of the rainfall field. Limited and inaccurate rainfall observations can negatively affect flood forecasting and the decision-making processes based on warning system. This problem becomes much more evident in urban catchments which usually covers huge areas and where the runoff process is faster, due to the highly impervious surfaces. Given this, it is a priority to develop always new operational instruments which can improve rainfall data availability and accurately quantify rainfall variability in space. To face this challenge, in the recent years, it has been investigated the use of commercial microwave links (CML) as opportunistic rainfall sensors which could be integrated with traditional rainfall observations in areas lacking sensors. The technique relies on the well-established relationship between CML's signal attenuation and rainfall intensity across the signal propagation path. Here, we assess the operational potential of a CML network, located in the northern area of Lambro river (Lombardia region, Italy). This urbanized region is of great hydrological interest, since it is often subjected to flash floods, hence it requires a robust and accurate warning system. We considered a set of about 80 CMLs distributed quite uniformly over the entire study area and we assessed if and how rainfall data collected by them can improve river discharge predictions. To this aim, we implemented a semi-distributed rainfall-runoff model, which reproduces the river flow at the outlet section in Lesmo (Monza e Brianza), and we fed the hydrological model with CML rainfall data. We tested the use of CML rainfall data as input to the hydrological model. In particular, we used path-averaged rainfall intensities, calculated from CML path attenuation, as point measurements with a weight inversely proportional to CML length. To check the suitability of CML data as input to our urban rainfall-runoff model, we compared the observed river discharge with the predicted one, obtained using different rainfall data layouts. Indeed, we tested CML data but also rain gauges measurements and a combination of CML and rain gauge observations.
Plume-induced subduction and plate fracturation, deep mantle overturn, and the onset of plate tectonics.
Authors: Davaille Anne
Published: March 2021

Mantle dynamics can now be recovered in the laboratory, when aqueous colloidal dispersions are dryed from above, and either insulated or heated from below. As their rheology varies from viscous to visco-elasto-plastic to brittle when drying proceeds, a skin (i.e. an experimental lithosphere) develops at the surface. Submitted to buckling, small-scale convection, or an impinging hot plume, this skin can break and one-sided subduction is then observed to proceed. In the case of plume-induced subduction (PIS), the impact of the plume under the skin induces tensile fractures, plume material upwelling through them and spreading at the surface, analogous to volcanic flooding, leading to skin bending and eventually one-sided subduction along arcuate segments which retreat away from the plume. A system of accreting ridges can develop inside the back-arc basin. If PIS develops isolated in an overall stagnant lithosphere, subduction eventually either stops as the result of subducted plate necking, or when plume spreading stops. On the other hand, if the lithosphere contains other heterogeneities (damage) such as faults, accretion ridges or another PIS event, the weight of the subducting plate can induce faraway plate breaking and horizontal mobilization of the surface plate.

As the lithosphere has to accumulate damage to fracture, it takes time from the first subduction event to the organization of a network of subducting and accreting plates. But the presence of several hot plumes simultaneously accelerates the establishment of an organized pattern of plates, subduction and accretion. And when we run experiments where the mantle contains initially a denser layer at the bottom, the global overturn of this dense layer results in the simultaneous generation of plumes over the whole mantle surface, which produces a burst of PIS events and the quick establishment of a plate tectonic-like regime. 
Such a global overturn has been proposed to explain the big peak in continental crust growth 2.7 Ga on Earth. Our experiments suggest that it could also have triggered the formation of the plates boundaries and flow organization necessary to plate tectonics.
Tearing instability inside a 2D current sheet with a normal magnetic field
Authors: Shi Chen , Artemyev Anton , Velli Marco , Tenerani Anna
Published: March 2021

Magnetic reconnection converts the magnetic field energy into thermal and kinetic energies of the plasma. This process usually happens at extremely fast speed and is therefore believed to be a fundamental mechanism to explain various explosive phenomena such as coronal mass ejections and planetary magnetospheric storms. How magnetic reconnection is triggered from the large magnetohydrodynamic (MHD) scales remains an open question, with some theoretical and numerical studies showing the tearing instability to be involved. Observations in the Earth’s magnetotail and near the magnetopause show that a finite normal magnetic field is usually present inside the reconnecting current sheet. Besides, such a normal field may also exist in the solar corona. However, how this normal magnetic field modifies the tearing instability is not thoroughly studied. Here we discuss the linear tearing instability inside a two-dimensional current sheet with a normal component of magnetic field where the magnetic tension force is balanced by ion flows parallel and anti-parallel to the magnetic field. We solve the dispersion relation of the tearing mode with wave vector parallel to the reconnecting magnetic field. Our results confirm that the finite normal magnetic field stabilizes the tearing mode and makes the mode oscillatory instead of purely growing.
Two extreme events near the Allerød-Younger Dryas transition: A story read from Bohemian Forest lake sediments (Central Europe)
Authors: Vondrák Daniel , Kletetschka Gunther , Svecova Eva , Hruba Jolana , Štorc Richard , Hrstka Tomas , Heurich Marco , van der Knaap Willem Oscar , Stuchlik Evzen
Published: March 2021

Near 12,850 cal. yr. BP, the Younger Dryas cooling (YD) abruptly reversed the warming trend from the last glacial to the present interglacial at high northern latitudes. Subsequent YD-onset-related changes, including hydroclimate shifts, affected ecosystems and human societies worldwide. The main YD trigger – e.g., a massive meltwater input into the North Atlantic Ocean, volcanic gas aerosols from the cataclysmic Laacher See (LS) eruption in the Volcanic Eifel, Germany, or an extraterrestrial body impact or airburst – remains widely debated and unclear. We have obtained lake sediment cores from three sites located in the Bohemian Forest Mts., Czechia-Germany-Austria border area (distance of 450–470 km from the LS volcanic crater). The characteristic LS tephra glass shards were documented in all three cores using X-ray fluorescence scanning, magnetic susceptibility measurements, and direct observation by scanning electron microscopy, and their concentrations were quantified by a TESCAN Integrated Mineral Analyzer (TIMA). Our geochemical results show the closest match with the so-called MLST-B phreatomagmatic phase of the LS eruption. Moreover, a significant amount of LS-(crypto)tephra-related phosphorus (up to 0.15%), often the limiting nutrient in both terrestrial and freshwater ecosystems, was found in the sediments. The discovery of the LS volcanic ash in the Bohemian Forest points to a wider distribution of this (crypto)tephra than has been known so far (evident transport also in the eastern direction). It opens up new potential for tephrochronologically supported research of Late-glacial sediments in eastern Central Europe and exploring the role of the event in human prehistory. In addition to the LS cryptotephra, we observed magnetically extracted iron-rich microspherules with signs of high-temperature melting and quenching in all studied sediment cores. Their maxima (3–36 objects per 1 g of dry sediment) were situated 2.2–3.1 cm above peaks in the LS tephra shard concentrations. Such exotic objects were reported from numerous sites on several continents where more impact-related proxies were documented by proponents of the YD impact hypothesis. Based on this evidence, we hypothesize that the Allerød-Younger Dryas transition in Central Europe was likely affected by more than one extreme event. The LS eruption was followed by an event during which the iron-rich microspherules were formed. The ongoing study is supported by the Czech Grant Foundation (20-08294S – PROGRESS).
Proglacial Lakes Elevate Glacier Surface Velocities in the Himalayan Region
Authors: Pronk Jan Bouke , Bolch Tobias , King Owen , Wouters Bert , Benn Douglas
Published: March 2021

Meltwater from Himalayan glaciers sustains the flow of rivers such as the Ganges and Brahmaputra on which over half a billion people depend for day-to-day needs. Upstream areas are likely to be affected substantially by climate change, and changes in the magnitude and timing of meltwater supply are likely to occur in coming decades. About 10 % of the Himalayan glacier population terminates into pro-glacial lakes and such lake-terminating glaciers are known to be capable of accelerating total mass losses. However, relatively little is known about the mechanisms driving exacerbated ice loss from lake-terminating glaciers in the Himalaya. Here we examine a 2017-2019 glacier surface velocity dataset, derived from Sentinel 2 imagery, covering most of the Central and Eastern Himalayan glaciers larger than 3 km2. We find that centre flow line velocities of lake-terminating glaciers are more than double those of land-terminating glaciers (18.8 vs 8.24 m yr-1) and show substantially more heterogeneity around glacier termini. We attribute this large heterogeneity to the varying influence of lakes on glacier dynamics, resulting in differential rates of dynamic thinning, which effects about half of the clean-ice lake-terminating glacier population. Also, numerical ice-flow model experiments suggest that changes at the frontal boundary condition can play a key role in accelerating the glacier flow at the front. With continued warming new lake development is likely to happen and will further accelerate future ice mass losses, a scenario not currently considered in regional projections. 
Impact of dilatant strengthening and energy dissipation on fault slip stability
Authors: Jacquey Antoine , Veveakis Manolis , Juanes Ruben
Published: March 2021

The temporal and spatial distribution of fluid pressure and temperature within a fault core are key determinants of the onset and nature (seismic or aseismic) of fault slip. Laboratory and field observations indicate that transient localization of fluid pressure and temperature often go hand in hand with strain localization upon seismic rupture: as slip occurs on a fault plane, temperature increases due to dissipated energy and fluid pressure decreases due to dilatant strengthening. An accurate description of this thermo-hydro-mechanical multiphysics coupling controlling slip mechanisms is therefore essential to characterize the stability of fault slip.

Here, we present results from analytical and numerical analyses of the stability of fault slip adopting a thermo-hydro-mechanical coupling scheme together with a rate-dependent plasticity formulation. In particular, we focus on the relevance of dilatant strengthening competing with energy dissipation as driving processes for stick-slip events and aseismic slip. We analyze the multiple steady states of the system and their respective stability by means of a numerical continuation technique, and we describe the dynamic evolution of deformation, fluid pressure and temperature fields by considering an associated transient problem.

The results presented here provide insights into the stability criterion for aseismic slip and the dynamic evolution of slip instability as a function of the physical (thermal and hydraulic) properties of the fault material and the boundary conditions (tectonic stresses and off-fault fluid pressure and temperature conditions). We identify two mechanisms for periodic slip, one driven by elastic loading and the other by multiphysics oscillations. We discuss the implications of these results for characterizing the transition from stable aseismic slip to unstable seismic slip in the context of natural and induced seismicity.
Decomposing local and remote surface temperature impacts of Asian aerosols
Authors: Merikanto Joonas , Nordling Kalle , Räisänen Petri , Räisänen Jouni , O'Donnell Declan , Partanen Antti-Ilari , Korhonen Hannele
Published: March 2021

We investigate how a regionally confined radiative forcing of South and East Asian aerosols translate into local and remote surface temperature responses across the globe. To do so, we carry out equilibrium climate simulations with and without modern day South and East Asian anthropogenic aerosols in two climate models with independent development histories (ECHAM6.1 and NorESM1).  We run the models with the same anthropogenic aerosol representations via MACv2-SP (a simple plume implementation of the 2nd version of the Max Planck Institute Aerosol Climatology). This leads to a near identical change in instantaneous direct and indirect aerosol forcing due to removal of Asian aerosols in the two models. We then robustly decompose and compare the energetic pathways that give rise to the global and regional surface temperature effects in the models by a novel temperature response decomposition method, which translated the changes in atmospheric and surface energy fluxes into surface temperature responses by using a concept of planetary emissivity.  

We find that the removal of South and East Asian anthropogenic aerosols leads to strong local warming  response from increased clear-sky shortwave radiation over the region, combined with opposing warming and cooling responses due to changes in cloud longwave and shortwave radiation. However, the local warming response is strongly modulated by the changes in horizontal atmospheric energy transport. Atmospheric energy transport and changes in clear-sky longwave radiation redistribute the surface temperature responses efficiently across the Northern hemisphere, and to a lesser extent also over the Southern hemisphere. The model-mean global surface temperature response to Asian anthropogenic aerosol removal is 0.26±0.04 °C (0.22±0.03 for ECHAM6.1 and 0.30±0.03 °C for NorESM1) of warming. Model-to-model differences in global surface temperature response mainly arise from differences in longwave cloud (0.01±0.01 for ECHAM6.1 and 0.05±0.01 °C for NorESM1) and shortwave cloud (0.03±0.03 for ECHAM6.1 and 0.07±0.02 °C for NorESM1) responses. The differences in cloud responses between the models also dominate the differences in regional temperature responses. In both models, the Northern hemispheric surface warming amplifies towards the Arctic, where the total temperature response is highly seasonal and modulated by seasonal changes in oceanic heat exchange and clear-sky longwave radiation.

We estimate that under a strong Asian aerosol mitigation policy tied with strong greenhouse gas mitigation (Shared Socioeconomic Pathway 1-1.9) the Asian aerosol reductions can add around 8 years’ worth of current day global warming during the next few decades.
Testing Slip Models for Tsunami Generation
Authors: Bayraktar Hafize Başak , Scala Antonio , Lorito Stefano , Volpe Manuela , Linares Carlos Sánchez , Festa Gaetano , Davies Gareth , Romano Fabrizio , Bernardi Fabrizio , Selva Jacopo , Macías Jorge , de la Asunción Marc , Castro Manuel J.
Published: March 2021

Tsunami hazard depends strongly on the slip distribution of a causative earthquake. Simplified uniform slip models lead to underestimating the tsunami wave height which would be generated by a more realistic heterogeneous slip distribution, both in the near-field and in the far-field of the tsunami source. Several approaches have been proposed to generate stochastic slip distributions for tsunami hazard calculations, including in some cases shallow slip amplification (Le Veque et al., 2016; Sepulveda et al., 2017; Davies 2019; Scala et al., 2020). However, due to the relative scarcity of tsunami data, the inter-comparison of these models and the calibration of their parameters against observations is a challenging yet very much needed task, also in view of their use for tsunami hazard assessment.

Davies (2019) compared a variety of approaches, which consider both depth-dependent and depth-independent slip models in subduction zones by comparing the simulated tsunami waveforms with DART records of 18 tsunami events in the Pacific Ocean. Model calibration was also proposed by Davies and Griffin (2020).

Here, to further progress along similar lines, we compare synthetic tsunamis produced by kinematic slip models obtained with teleseismic inversions from Ye et al. (2016) and by recent stochastic slip generation techniques (Scala et al., 2020) against tsunami observations at open ocean DART buoys, for the same 18 earthquakes and ensuing tsunamis analyzed by Davies (2019). Given the magnitude and location of the real earthquakes, we consider ensembles of consistent slipping areas and slip distributions, accounting for both constant and depth-dependent rigidity models. Tsunami simulations are performed for about 68.000 scenarios in total, using the Tsunami-HySEA code (Macías et al., 2016). The simulated results are validated and compared to the DART observations in the same framework considered by Davies (2019).
Evaluation of ICESat-2 ATL03 and ATL13 River Levels in Mountainous Areas of China
Authors: Ranndal Heidi , Nielsen Karina , Andersen Ole B.
Published: March 2021

The data from NASA’s Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) mission offer a unique opportunity to map rivers and lakes with an unprecedented number of observations in areas where previous missions have failed to provide valuable water level estimates. ICESat-2 carries just one instrument, the Advanced Topographic Laser Altimeter System (ATLAS), which is a green wavelength, photon-counting lidar, and several data products are available, such as the ATL03 product, which holds the photon data, and the ATL13 product which contains estimated inland water surface heights and statistics for water bodies across the world. The along-track resolution of the ATL03 product is less than 1 m, and with the three pairs of beams, i.e. six beams in total, the mission provides exceptional opportunities for inland water studies in areas with mountainous topography.

In general, inland water altimetry in mountainous areas has proven to be a challenge for both conventional Low Resolution Mode (LRM) and Synthetic Aperture Radar (SAR) altimetry, causing issues not only with waveforms, but also the position of the range window. In this study, we present the ability of ICESat-2 to obtain water levels in several mountainous rivers in China, where even SAR missions such as CryoSat-2 and Sentinel-3 have been unsuccessful. Results are shown for both the ATL03 and the ATL13 version 4 products to evaluate their performances.
Electrical properties of the lithosphere in the western desert, Egypt, using magnetotelluric sounding
Authors: Marzouk Hossam , Arafa-Hamed Tarek , Becken Michael , Abdel Zaher Mohamed , Comeau Matthew
Published: March 2021

We present electrical resistivity models of the crust and upper mantle estimated from 2D inversions of broadband magnetotellurics (MT) data acquired from two profiles in the western desert of Egypt, which can contribute to the understanding of the structural setup of this region. The first profile data are collected from 14 stations along a 250 km profile, in EW direction profile runs along latitude ~25.5°N from Kharga oasis to Dakhla oasis. The second profile comprises 19 stations measured along a 130 km profile in NS direction centered at longitude 28°E and crossing the Farafra. The acquisition for both profiles continued for 1 to 3 days at each station, which allowed for the calculation of impedances for periods from 0.01 sec up to  4096 sec at some sites. The wide frequency band corresponds to a maximal skin depths of up to 150 km that can provide penetration to the top of the asthenosphere. The inversion models display high-conductivity sediments cover at the near surface (<1-2 km), which can be associated with the Nubian aquifer. Along the EW-profile from Kaharge to Dhakla, the crustal basement is overly highly resistive and homogeneous und underlain by a more conductive lithospheric mantle below depths of 30-40 km. Along the N-S profile across Farafra, only the southern portion exhibits a highly resistive crust, whereas beneath Farafra northwards, moderate crustal conductivities are encountered. A comparison has been made between the resultant resistivity models with the 1° tessellated updated crust and lithospheric model of the Earth (LITHO1.0) which was developed by Pasyanos, 2014 on the basis of seismic velocity data. The obtained results show a remarkable consistency between the resistivity models and the calculated crustal boundaries. Especially at the Kharga-Dakhla profile a clear matching can be noticed at the upper and lower boundaries of a characteristic anomaly with the Moho and LAB boundaries respectively.