bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical investigation of the coastal dynamics over the western Black sea
Authors: Shamsnia S. Hadi , Bellafiore Debora , Ferrarin Christian , Bajo Marco
Published: February 2023

The Black Sea is one of the largest enclosed seas in the world. More than 160 million people live in its coastal areas and large rivers flow into it, as  the Danube, the Dniester, the Dnieper and the Don. The Danube river, located on the western coast, is the most important European waterway whose catchment area is shared by more than fifteen countries. Black sea coastal waters are also often characterized by high suspended sediment concentrations derived from coastal runoff and local sediment re-suspension from the river sources. Measuring coastal sediment transport in field situations is notoriously difficult and generally subject to great uncertainty, and model estimates are often used in practice. The specific objectives of the current study are to understand the present state of the western Black Sea, and to study current and wave dynamics with the assistance of state-of-the-art numerical models for simulating waves, currents, and their interactions with the sediment loads. We used the hydrodynamic model named SHYFEM, hard coupled with the Wavewatch III wave model for the current study, while the coupled Sedtrans05 model will be used in the future for sediment modeling. The numerical models are applied on an unstructured grid representing the western Black Sea and the Danube Delta through the use of triangular elements of different shapes and sizes.The simulations of the coupled SHYFEM-WW3 were compared with the significant wave heights (Hs) measured by the Jason-3 and Sentinel-3. Despite some discrepancies, SHYFEM-WW3 provides good agreements with the altimeter data. The preliminary comparison done on the basin scale application show better performance of the model for the western area (Correlation coefficient = 0.89 in the western Black sea, while Correlation coefficient = 0.81 in the basin scale). Next steps will be dedicated to a coastal application on the western Black Sea coupling circulation, waves and sediment transport.All of the modeling activities are developed within the framework and funded by the Horizon 2020 DOORS (Developing Optimal and Open Research support for the Black sea) project, (Grant no. 101000518) https://www.doorsblacksea.eu/.
Analysis of extreme temperature events based on estimated 1-km daily near-surface air temperature
Authors: Wang Bin , Gao Meiling , Li Zhenhong
Published: February 2023

Nowadays, the intensification of global warming leads to the increased frequency of extreme temperature events. Many studies reported that different regions are facing the threat of extreme hot and cold temperature in some degree. The Qinghai-Tibet Plateau Transportation Project is a major project in China, and it is beneficial for public to study the extreme temperature events along the railway and avoid the risk induced by the extreme temperature. This study estimated the daily maximum, minimum and average near-surface air temperature along the railway. Sixteen extreme temperature indices defined by ETCCDI (the Expert Team on Climate Change Detection and Indicators) were used to represent the extreme temperature events, and Mann-Kendall trend test and Sen's slope estimation method were employed to explore the spatial-temporal variation trends of the extreme temperature along the Qinghai-Tibet Plateau Transportation Corridor from 1981 to 2019. In addition, the response of extreme temperature events to altitude was discussed.The results show that the climate becomes warming along the Qinghai-Tibet Plateau Transportation Corridor from 1981 to 2019, and the extreme hot events are detected in most areas, while the extreme cold events mainly occurs in the east and southwest part. The significant increasing trend is found according to the indices representing the hot events (SU25, TR20, TX90p, TN90p, TXx, TXn, TNx, TNn and WSDI), while the indices representing the cold events (FD0, ID15, TX10p, TN10p and CSDI) show a significant decreasing trend in most areas over the past nearly 40 years. Besides, the extreme temperature events is highly related to altitude variations. Compared with the middle altitude zones, extreme high temperature events tend to occur in the lower altitude zones and the higher altitude zones. It is of great significant to schedule the train in advance and reduce the disasters by investigating the long-term variation trends of extreme temperature events along the Qinghai-Tibet Plateau Transportation Corridor.
Effect of Rainfall Fractal Behaviour on that of Recharge and Groundwater Levels
Authors: Habib Abrar , Paschalis Athanasios , Butler Adrian P. , Onof Christian , Bloomfield John P. , Sorensen James P. R.
Published: February 2023

Using a physically based recharge-groundwater flow model, a multiplicative random cascade rainfall model and robust detrended fluctuation analysis (r-DFA), the effect of the fractal behaviour of rainfall on recharge and groundwater levels is investigated. The study site selected for this work is in Wallingford, United Kingdom, where groundwater levels in a shallow riparian aquifer and meteorological data of high temporal resolution are monitored.
The rainfall model is calibrated to the observed rainfall and used to simulate 40 synthetic rainfall series exhibiting different scaling behaviour (with r-DFA scaling exponents between 0.6 and 1.05). The scaling behaviour of the rainfall series are then objectively quantified using r-DFA. The synthetic rainfall is used as forcing to run the recharge-groundwater flow model which is calibrated to the observed groundwater levels.
It is found that small changes in the fractal behaviour of rainfall has a significant effect on the fractal behaviour of recharge and this in turn results in a small change in the fractal behaviour of groundwater levels. The significant effect on the fractal behaviour of drainage is attributed to the extended recharge periods which correspond to more frequent rain events in rainfall with higher scaling exponents. This effect is more subdued in groundwater level fluctuations due to attenuation of the recharge signal as it percolates through the unsaturated zone.
Large scale two-source energy balance modelling of evapotranspiration over Mediterranean region
Authors: Bartkowiak Paulina , Castelli Mariapina , Ventura Bartolomeo , Jacob Alexander
Published: February 2023

Remote sensing data play an important role in understanding the spatio-temporal variations in hydro-meteorological conditions at different spatial scales. In particular, one of the key processes of hydrological cycle for monitoring water loss from space is evapotranspiration (ET). In contrast to sparsely distributed in-situ measurements, development of two surface energy balance (TSEB) models forced by satellite observations has made a significant contribution to estimate ET with global coverage. In this regard, in the framework of ESA’s 4DMED-Hydrology project, we combine Copernicus data from Sentinel-2 (S2) Multispectral Instrument (MSI) and Sentinel-3 (S3) Land Surface Temperature Radiometer (SLSTR) with ERA5 climate reanalysis dataset derived within the period 2017-2021 for daily ET retrieval at high (100 m) spatial resolution. In this work, an open-source implementation of TSEB developed in the framework of the ESA’s Sen-ET project has been applied over wide areas represented by four Mediterranean basins in Italy, Spain, France, and Tunisia (Po, Ebro, Hérault and Medjerda). Considering large volume of satellite data and high computational requirements of the Sen-ET, all processes have been optimized to be run in the automatic manner by combining multiple steps into one processing workflow utilized in cloud computing platforms offered by EODC and ESA HPC of CloudFerro. First, due to incomplete time-series of S2 Level-2A, we pre-process Sentinel-2 data for further retrieval of 100-m reflectance and biophysical parameters needed for the ET estimation afterwards. Next, we downscale S3 land surface temperature (LST) product by exploiting relationships between 1-km Sentinel-3 and time-coincident 100-m S2 reflectances using decision trees (DT) algorithm. Apart from biophysical properties (e.g., leaf area index and fractional vegetation cover) and sharpened LST data, meteorological forcings and solar radiation from ERA5 have been generated for estimating instantaneous energy fluxes and daily evapotranspiration. Based on preliminary results over Po basin, DT algorithm allowed predicting 100-m LST with the average root mean square error (RMSE) of 3.2°C when compared to ground-derived skin temperature from two eddy covariance (EC) towers. Meanwhile, turbulent fluxes driven by downscaled LST resulted in RMSE equal to 52 Wm-2 and 108 Wm-2 for sensible and latent heat fluxes, respectively. Despite some limitations mainly related to the EC locations in complex mountain areas, ET estimates forced by satellite observations have potential for providing energy fluxes at wider scale.Keywords: evapotranspiration, Sentinel-3, land surface temperature, Mediterranean region
Modelling Jupiter's global and regional magnetic fields using physics-informed neural networks
Authors: Chen Longwei , Livermore Phil , Wu Leyuan , de Ridder Sjoerd , Zhang Chong
Published: February 2023

As is known, neural networks can universally approximate any complex functions. This ground truth naturally makes it a suitable candidate for solution representation of complex partial differential equation (PDE) governed. For planetary magnetic field modelling problem, spherical harmonic functions are most used as standard modelling method. Spherical harmonic method requires globally nearly uniformly distributed observations. Meanwhile this method has quite limited ability for conducting regional field modelling. Instead, neural networks have great potential to deal with global or regional modelling problems. In this work, we thoroughly investigate the representative ability of neural networks for magnetic field modelling problem at global and regional scale, and concentrate on a specific neural network, that is physics-informed neural networks (PINNs) for implementation. PINNs makes it easier to incorporate different kinds of informed physics within a uniform optimization framework. Through synthetic model tests and partial mathematical proof, we showcase the importance of employing natural boundary condition, Laplace equation constraint and Poisson equation constraint at suitable collocation points for a reasonable and accurate magnetic field representation and introduce the detailed scheme for implementation. Finally, we use newly released Juno mission measurements, and present a global PINNs model for Jupiter's magnetic field, and a regional PINNs model for Great Blue Spot (GBS) region. Comparison with spherical harmonic model has been conducted to evaluate the correctness and flexibility of PINNs models.
Crustal structure beneath the Western Himalayas from surface wave dispersion analysis
Authors: Biswal Shubhasmita , Kumar Sushil
Published: February 2023

The Western Himalaya is one of the most complex and heterogeneous seismotectonic units of the Alpide-Himalaya seismic belt. The region has distinctive physiographic characteristics because of the way that they have changed and evolved over the course of time. The purpose of the present investigation is to understand the seismotectonic architecture beneath the study area which is seismically very active. Twenty broad-band seismic stations have been employed to record the surface wave data to study the crustal structure beneath the western Himalayas. We find phase and group velocities of Rayleigh waves for the region with periods between 4 and 30s. To obtain layered S wave velocity models, the dispersion curves are inverted. The crustal velocity structure beneath the region is found to vary significantly. The average estimated S-wave velocity is ~ 3.8 km/s down to 30 km depth. We also observed a low-velocity layer in the middle crust of the higher Himalayas section and the interpretation from the present analysis is consistent with available geological data. 
Uncertainty quantification of geophysical models constructed by surface geometry inversion using Markov chain Monte Carlo sampling
Authors: Lu Xushan , Lelièvre Peter , Farquharson Colin
Published: February 2023

Conventional Occam-style, minimum-structure inversion methods typically do not recover models with distinct boundaries between different geological units. Consequently, the constructed geophysical model can be very different from the true geological model and difficult to interpret in the geological context. This can be especially problematic for geological models with very thin structures that have a large physical property contrast with the background model, and determining the location of which is critical to, e.g., an exploration program. We have developed a new inversion method called surface geometry inversion which can construct geophysical models with distinct interfaces. The algorithm parameterizes the interface between geological units with triangular facets of connected nodes (vertices) and then inverts for the coordinates of these nodes. The algorithm only focuses on the boundary interface of localized anomalies and assumes the background model is known. Consequently, it is useful to have an adequately developed geological model and sufficient physical property data on which to base a background model. After the inversion, a model comprised of the background model and the anomalous region is constructed. We then utilize Markov chain Monte Carlo sampling to obtain statistical information, namely, the mean and standard deviation of the nodal coordinates of the constructed model. The standard deviation of each node is then used as an indicator of model uncertainty. The uncertainty information is useful as it can help us obtain a better understanding about the geological model. When applied to mineral exploration, the uncertainty quantification can also be used to mitigate the risks in drilling activities. We present synthetic transient electromagnetic data inversion examples with thin graphitic fault models. We also present a real-data example where transient electromagnetic data are used to target thin graphitic faults for a uranium exploration project.
The Biogeochemistry of Drought
Authors: Schimel Joshua
Published: February 2023

Much of the Earth experiences regular drought, however, the processes occurring during the dry season remain unexplained, such as the "Birch Effect"—the pulse of respiration on rewetting a dry soil, or why, during the summer in California grasslands, microbial biomass increases. These changes result from a combination of microbial drought survival physiologies coupled to the physical dynamics of the soil system. Although many studies have emphasized microbial responses to drought and have looked to such mechanisms to explain the Birch Effect, it appears more likely that that the mobilization of bioavailable C is a result of physical/chemical forces that mobilize C upon rewetting. This talk will focus on how we bridge the scales from the micro- to the ecosystem: how can we incorporate the dry-soil and pulse processes into large-scale models of soil carbon processes? 
The strength of CO2 fertilization in forests inferred from the eddy-covariance record
Authors: Zhan Chunhui , Orth René , Yang Hui , Reichstein Markus , Zaehle Sönke , Rammig Anja , Winkler Alexander
Published: February 2023

Carbon sequestration, particularly in forests, is assumed to increase with increasing atmospheric CO2 concentrations due to the CO2 fertilization effect on photosynthesis (CFE). Estimating the contemporary effect of increasing atmospheric CO2 on continuous measurements of gross primary production (GPP) in forest stands is still lacking as it is challenging to disentangle the CFE from other effects on GPP acting on long time scales such as climate variability, succession, land-cover change, and nutrient deposition. Here we introduce a statistical method, i.e., the “GPP residual” method, to estimate the effect of climate on GPP based on short-term variability, to remove it from the long-term signal, yielding the GPP residual that can be, at least partly, attributed to CFE.We validate the applicability of this “GPP residual” method by testing whether it can accurately identify the CFE in simulations of the process-based land surface model QUINCY (QUantifying Interactions between terrestrial Nutrient CYcles and the climate system). We compare (i) the difference in the simulated GPP between historical simulations forced with transient and constant CO2 concentrations with (ii) the non-climatic GPP variations determined when applying the “GPP residual” method to the transient-CO2 simulation, and find encouraging agreement.We next apply our approach to eddy-covariance derived GPP at 32 forested sites located in Europe and the US to quantify the CFE for each site and month-of-year in growing seasons. The median CFE across all site-months is 22 ± 6 % per 100 ppm change in CO2. We note that other effects, such as nitrogen deposition and land management, also influence the GPP residual and could be incorrectly attributed to CFE. Assuming that these more site-specific effects may partially cancel out across sites as random effects, the estimated median value still reflects the strength of CFE. However, causal research will be needed to disentangle these long-term effects which cannot be separated by time scale.In summary, our study derives for the first time an observation-based estimation of the CO2 fertilization effect across forested ecosystems based on the eddy covariance record. Our results encourage future work to reconcile the uncertainties of the effect of increasing CO2 on the global carbon cycle as determined from models, experiments and observations.
Pdiff Coda Waves as the Result of Distributed Whole-Mantle Scattering
Authors: Sens-Schönfelder Christoph , Zhang Tuo , Bianchi Marcelo , Bataille Klaus
Published: February 2023

Seismic energy that follows the theoretical arrival time of the Pdiff phase is usually regarded as Pdiff coda. This implies its generation by scattering of diffracted P-waves. Such waves can theoretically be observed in the core shadow from 100° up the antipode in the time window extending from the theoretical arrival of the Pdiff phase until the arrival of the next direct phase which is PP or a core phase.However, scattered energy is also observed at frequencies above 1Hz where diffraction is inefficient. We present observations of scattered energy arriving more than 100s prior to PKP at distances exceeding 150° with an emergent shape and in the complete absence of a direct Pdiff arrival. These observations exclude a connection to a diffracted P-wave. Modelling of the seismic energy propagation with radiative transfer theory in an independently established model of mantle heterogeneity confirms that the scattered seismic energy in the Pdiff coda time-distance window has its origin in scattering of P-waves in the whole mantle. We demonstrate that different depth layers contribute to different arrival times in the scattered wave train which explains the emergent shape of the wave train and provides means to improve the depth resolution of current heterogeneity models. These findings confirm earlier interpretations that connected Pdiff coda with mantle scattering. They are also compatible with array observations that show an extinction of the direct P_diff phase towards 107° above 1Hz, because even the seemingly direct arrival of Pdiff at distances shortern than 130° can be mimicked by mantle scattering, as our modelling shows. The observed energy is thus more directly related to P-coda or PP-precursors than to the Pdiff phase.
Wave-particle interactions in the Earth magnetotail during dipolarization
Authors: Kozak Liudmyla , Petrenko Bohdan , Kronberg Elena , Akhmetshyn Roman , Ballai Istvan
Published: February 2023

The energy of particles in the Earth's magnetosphere changes significantly when the configuration of the magnetic field lines suddenly changes from stretched to more dipolar (dipolarization). Energy changes can be caused by variation in electric fields,  due to the generation of electrostatic waves, etc. The presence of heavy ions at the heights of the magnetosphere significantly changes the physics of the processes since, in addition to changing the main characteristics of the plasma (temperature, pressure, Alfven velocity thickness of the current/plasma layer), the conditions and rate of development of instabilities (in particular, the Kelvin-Helmholtz instability) and the nature of turbulent processes will change as well.In this work, the change of ion and electron fluxes is considered and the peculiarities of resonant interaction of charged particles with electromagnetic fluctuations during the dipolarizations are determined.The data from the Cluster-II mission spacecraft (magnetic field measurements from ferroelectrode magnetometers (FGM) and energetic particle fluxes from RAPID spectrometers) were used for the analysis. The analysis of individual events is carried out, and a statistical consideration of changes in particle fluxes during magnetic field dipolarizations for 2001–2015 is presented.Among the features of proton fluxes for individual events, an non-correlation between flux changes in different energy channels is recorded (example, the flux at 27 keV is approximately constant, and is peaks in higher energy ranges). Thus, we have a selective non-adiabatic acceleration of a part of a proton spectrum depending on energy. The change of the spectral index for different energy channels and components was studied.The values of the power of magnetic field oscillations at gyrofrequencies for different ion types obtained by epoch superposition method showed that resonant interactions of ions with low-frequency electromagnetic waves are more significant for "heavier" components. Therefore the ions can effectively be accelerated by the interaction with these waves during the dipolarization.This work was supported by the grant no. 97742 of the Volkswagen Foundation (VW-Stiftung), the Royal Society International Exchanges Scheme 2021 IES\R1\211177, and BF/30-2021.
Spatiotemporal rock moisture distribution at the medieval cave town of Uplistsikhe, Georgia
Authors: Sass Oliver , Fruhmann Stefanie
Published: February 2023

Moisture and salts cause considerable damage to built and rock-hewn heritage. Rock moisture is a key factor for numerous decay processes, but there is limited knowledge of salt and moisture distribution because measurements of spatial and temporal moisture distribution still remain challenging. The medieval cave town of Uplistsikhe (Georgia) is hewn out of very soft Lower Miocene sandstone and is a typical example of a heritage site suffering from progressive decay. We present data on moisture and salt distribution derived from a multi-method approach, including microwave sensor monitoring (MW-mon; continuously over 2 yrs), microwave handheld sensors (MW), 2D-resistivity profiles (ERT), rock sampling by drilling, and salt extraction by paper pulp poultices (PPP).Microwave monitoring was applied for the first time (to our knowledge) in a long-term monitoring of heritage sites. We used equipment from hf-sensor (Germany) with two types of microwave reflectivity sensors penetrating approx. 7 cm and 13 cm deep, respectively. The sensors were installed inside and outside of two prominent caves (Grand Hall and Long Hall). MW, ERT, PPP and drilling were carried out in four caves (the two mentioned plus Blackberry Hall and Teatron). Careful laboratory calibration using samples from the site was necessary to produce quantitative results for MW-mon, MW and ERT.  MW-mon showed pronounced annual fluctuation with highest moisture saturation occurring in summer. The moisture maximum in the caves lags 2 months behind the spring precipitation maximum and might be partly caused by air humidity condensation amplified by salts. Heavy rainfall events cause additional moisture pulses by seeping through the rock or by capillary rise. Spatial moisture distribution derived from MW shows relatively dry rock outside the caves and different patterns of moisture ingress into the caves: Capillary rise from the base, ingress through fractured or otherwise water-permeable areas of the roofs or back walls. The spatial patterns are confirmed by ERT; however, calculated moisture saturation differs between MW and ERT due to electrical conductivity effects of salty pore water.All drill samples from the caves are significantly saltier on the respective surfaces, which points to the rate of evaporation being smaller than the outward migration of salts. Outside the caves, flaking of thicker layers (several cm) point to deeper layers of salt concentration caused by higher evaporation from the surface; flaking at the "lips" above the caves is probably also amplified by stronger temperature and moisture fluctuations. The main ions everywhere are  Ca2+ and SO42- (subordinate K+) while at the strongly flaking surfaces of Grand Hall, Na+, Cl- and NO32- are also present. Summing up, the results show very diverse and complex patterns of moisture and salt distribution at an apparently homogeneous site.
Automatic detection of landslides from satellite images using a range of training events
Authors: Leeming Kathryn , Gonzalez Alvarez Itahisa , Novellino Alessandro , Taylor Sophie
Published: February 2023

Landslides in remote or uninhabited regions can be undocumented, leaving gaps in landslide inventories which are a key input for hazard and risk assessments. This can lead to landslide events being missing from research studies, and contribute to a bias in the events used for training of machine learning models.In this work we use satellite images, terrain information, and labelled examples of landslides to train a convolutional neural network (U-Net), for the purpose of adding previously undocumented and new landslides to inventories. This model segments the input images and highlights the pixels it labels as landslides.Our work focusses on landslides with a range of types and triggers, so that the model is exposed to a variety of training data. We describe the key properties of the landslides in the training set, and discuss the implications for future uses of the trained model.
Enhanced and gap-free Sentinel-2 reflectance data at vast scales with GEE
Authors: Izquierdo-Verdiguier Emma , Moreno-Martínez Álvaro , Muñoz-Mari Jordi , Clinton Nicolas , Vuolo Francesco , Atzberger Clement , Camps-Valls Gustau
Published: February 2023

The presence of clouds and aerosols in satellite imagery hamper their use to monitor, observe and analyze the Earth's surface. Multisensor fusion can alleviate this problem. The HISTARFM algorithm developed by Moreno-Martinez et al. (2020) can generate monthly gap-filled reflectance data at 30 m spatial resolution by blending Landsat (30 m pixel size every 16 days) and MODIS (500 m pixel size daily) data using a bias-aware Kalman filter. Cloud computing platforms such as Google Earth Engine (GEE) help us to efficiently process public data archives from different remote sensing data sources. Therefore, GEE allows us to adapt the HISTARFM algorithm to obtain gap-filled data at higher spatial resolution. To reduce the massive number of images involved in the process, the bias-aware Kalman filter blends the available and preprocessed HISTARFM monthly gap-filled reflectance (30 m pixel size every month) and Sentinel-2 (10 m pixel size at five days) data. The very high spatial gap-filled images provide reflectance information at feasible scales to obtain new products that improve decision-making activities in variable territories with complex topographies. Also, new derivative products (e.g. land cover maps, biophysical parameters, or phenological indicators) will provide the scientific community better understanding and monitoring of bio-geographical and ecoclimatic characteristics of the Earth.Additionally, a reduction of the time resolution of the temporal series is manageable with this approach by linear interpolation producing five days of gap-filled reflectance Sentinel-2 data. The proposed approach shows promising preliminary results and provides gap-free reflectance Sentinel-2 images with their associated uncertainties. These results foster the development of improved near-real-time applications for crop and natural vegetation monitoring at continental scales.
Landslide hydro-meteorological thresholds in Rwanda
Authors: Uwihirwe Judith , Hrachowitz Markus , Bogaard Thom
Published: February 2023

For the development of regional landslide early warning systems, empirical-statistical thresholds are of crucial importance. The thresholds indicate the meteorological and hydrological conditions initiating landslides and are an affordable approach towards reducing people’s vulnerability to landslide hazards. This research defined different landslide hydro-meteorological thresholds in Rwanda and evaluated their predictive capabilities. We identified the key hydro-geological and meteorological parameters in landslide-prone hillslopes in Rwanda. Precipitation was identified as the most important trigger of landslides and is of course the source of other hydrological processes and stocks such as local and regional groundwater levels and soil moisture content that predispose the slope to near failure. We therefore defined the precipitation-based threshold using rainfall and antecedent precipitation index as a proxy for the soil wetness state. The landslide precipitation thresholds served as an important first step towards the development of early warning system in Rwanda but constrained by the resulting quite high rate of false alarms. To improve the landslide prediction capability, the regional groundwater level was integrated in the landslide hazard assessment thresholds as a proxy for the catchments storage, an important hydrological processes that predispose the slope to near failure. This approach significantly improved the landslide prediction capability with high rate of true alarms and low rate of false alarms. However, given the scarcity of on-site data, the coarse spatial distribution network of the hydrological and meteorological recording equipment, themselves recording data at point scale, we have tested the potential of satellite and hydrological model-derived information in landslide hazard assessment thresholds. The GPM-based IMERG satellite precipitation product was found as a good alternate source of rainfall data for landslide hazard assessment in Rwanda. The hydrological model-derived soil moisture time series broadly reproduce the most important trends of the in-situ soil moisture and proved to be useful for landslide hazard assessment. The hydro-meteorological threshold models that incorporate the antecedent soil moisture content at root zone and the cumulative 3day rainfall reveal promising results. Based on the overall comparison, the landslide hydro-meteorological thresholds that consider the pre-wetting conditions of the terrain using groundwater levels and soil moisture at the root zone improved the landslide prediction as compared to the exclusive use of the classical precipitation thresholds such as intensity-duration I-D and event-duration E-D. The hydrological processes are concluded to be the most important landslide predictors potentially useful for a robust landslide early warning system development in Rwanda.
An updated view on water masses on the Northeast Greenland shelf and their link to the Laptev Sea and Lena River
Authors: Willcox Esty , Bendtsen Jørgen , Mortensen John , Mohn Christian , Lemes Marcos , Juul-Pedersen Thomas , Seidenkrantz Marit-Solveig , Holding Johnna , Møller Eva , Sejr Mikael , Rysgaard Søren
Published: February 2023

The Northeast Greenland shelf is a broad Arctic shelf located between Greenland and Fram Strait. It is the principal gateway for sea ice export and sea ice-associated freshwater from the Arctic Ocean. Sea ice thickness has decreased by 15% per decade since the early 1990s and meteoric freshwater discharge has increased. The consequence of changing sea-ice and freshwater conditions in the region on ocean dynamics and the biological system remains unknown. Determining the source(s) of freshwater is important to be able to understand how the area will react to future upstream change. Here we present a synoptic survey of the Northeast Greenland shelf and slope with observations of hydrography, the nutrients nitrate, phosphate and silicate, and conservative tracers δ18O, δ2H and total alkalinity during late summer 2017. We compare these to previously published values, including those which identify Pacific and Atlantic water, the Siberian shelf seas, and the 6 largest Arctic rivers. We show that a major source of freshwater on the Northeast Greenland shelf during late summer 2017 is the Laptev Sea and find no conclusive evidence of Pacific Water. Our observations provide a direct link between Northeast Greenland hydrology and processes occurring on Eurasian shelves.
Global energy budget changes from underestimated land heat uptake in CMIP6 models
Authors: Steinert Norman Julius , González-Rouco Jesús Fidel , de Vrese Philipp , Cuesta-Valero Francisco José , García Pereira Félix , Melo Aguilar Camilo Andrés
Published: February 2023

Under current climate-change conditions, the energy imbalance at the top of the atmosphere results in an uptake of energy by the Earth system. Previous efforts have identified the magnitude and proportions of this energy excess and how it is distributed among the different components of the climate system. However, the bulk of the Earth System Models (ESMs) participating in CMIP5/6 deliver Earth energy inventory estimates that differ substantially from recent observations. Particularly for the land component, there is a significant underestimation of simulated continental energy uptake, which was hypothesized to be caused by too shallow land surface model components in current-generation ESMs. Support for the latter was given by previous modeling estimates based on analytical heat conduction models and standalone land surface model simulations. Here we use a suite of current-generation fully-coupled CMIP6 ESMs and a version of the MPI-ESM that includes a deep land model component, accommodating the required space for increased terrestrial energy storage. The simulations show that a sufficiently deep land model leads to more realistic subsurface energy storage - correlating with model depth rather than climate sensitivity, and an adjusted estimate of energy uptake ratios among the Earth system components compared to observational estimates. However, the impact of changes in the land energy budget from the perspective of the entire Earth system appears to have only a marginal influence due to its relatively small fraction of the Earth energy inventory.
Long-term variability of Rossby Wave Breaking events over the Indian subcontinent
Authors: Thomas Biyo , Kunchala Ravi Kumar , Singh Bhupendra Bahadur , Kondapalli Niranjan Kumar
Published: February 2023

The synoptic scale upper level Rossby wave breaking (RWB) has a great influence on the weather pattern on the underlying regions. The RWB events have been studied extensively in the mid-latitude regions as it is prone to such events which often lead to extreme weather conditions. However, studies are elusive especially over the Indian sub-continent except few cases. RWB climatology and variability on monthly, interannual as well as on decadal scales is still poorly understood over this region. To address these shortcomings, in this study, we have used the reanalysis data and implemented a contour searching algorithm to identify RWB events over the period 1979-2021. Using the implemented algorithm, we have detected 513 RWB events for the study period which we further use to examine RWB climatology and variability over the subcontinent (5-40oN, 55-105oE). Our results suggest a significant increase in the number of RWB events per year during the last  two decades, as well as an increase in the intensity over the northwest region of the Indian subcontinent. We note that the RWB frequently affects the northwest region in winter, which later shows a shift in peak number of occurrences of RWB towards central India at the end of winter. This shift is linked to seasonal changes in the background zonal wind in the upper-troposphere. Also, the monthly climatology of vertical intrusions of the PV streamers indicate that intrusions are stronger during winter than other months. In addition, the role of RWB on the dynamical changes of the atmosphere such as anomalies of wind circulation patterns and moisture content is analyzed using composite analysis. The variability of the RWB events and its linkages with global sea surface temperature particularly conditions in the Pacific Ocean have also been studied.
Paleoenvironmental reconstruction of the southern extension of the Tiber delta with the Ostia palaeo lagoon: interplay between human activity and landscape change
Authors: Alessandri Luca , Bulian Francesca , de Neef Wieke , Dee Michael W , du Plessis John , Attema Peter , Sevink Jan
Published: February 2023

As today, in antiquity the importance of coastal and deltaic environments lay in the sea’s integrating role in the subsistence, resources, and trade opportunities of its people. For the first large towns of the late Bronze/early Iron Age in Central Italy, salt was an indispensable commodity being the only means available to preserve food, both for consumption and trade. It was produced in the coastal areas but the early production sites, techniques employed, and trade are still uncertain/poorly understood.            In the southern part of the Tiber delta palaeo-lagoon of Ostia, at the archeological site of Piscina Torta, heaps made of hundreds of thousands of potsherds were found, possibly related to the salt production technique known as briquetage and pointing at the existence of a major early salt production and trading industry. This coastal area likely holds an outstanding record of the Late Holocene paleoenvironmental changes and of the interaction between climatic variations and coastal processes in an area actively modified and adapted by human activity.            An intensive coring campaign at the site and subsequent analyses led to the identification of three stages in the development of the lagoon and its palaeo-inlet towards the sea. During the first phase, the lagoon was well connected to the sea and filled with marine sands. Later on, the inlet was blocked by a newly formed beach ridge, and peat accumulation started. During this second stage, the margins of both the lagoon and inlet were characterized by a highly evaporative environment with carbonate precipitation. Most probably, these sediments were used and leached for producing the brine needed for the salt production by briquetage, a method which consists in boiling such brine in typical reddish jars to obtain a salt cake. Furthermore, heaps composed of both inlet fill, and pottery found around the archeological site suggest how the channel connecting the sea with the lagoon may have been modified by anthropic activities. In a last (third) phase, presumably of medieval age, a marine transgression led to inundation of the lagoon and deposition of highly fossiliferous fine textured sediments.In this contribution, we show the results of a detailed geochemical and micropaleontological analysis (benthic foraminifers) of a continuous section sampled in the ancient lagoon of Ostia, in the form of a paleoenvironmental reconstruction of the area before, during and after its human occupation. Radiocarbon dates provide a firm time frame for the palaeo-lagoon evolutionary phases, while grain size analyses performed both on the inlet fill and the sediment heaps found at the site, revealed new details regarding the human modification of the landscape.
Large-scale remote sensing exploration of the resilience of Iberian holm oak woodlands to extreme droughts
Authors: Moreno de las Heras Mariano , Bochet Esther , Vicente-Serrano Sergio , Espigares Tiscar , Molina María José , Monleón Vicente , Nicolau José Manuel , Tormo Jaume , García-Fayos Patricio
Published: February 2023

The organization and function of forest ecosystems is changing at an unprecedent rate under the influence of external drivers, such as climate change and human uses. In this context of change, the increasing frequency, intensity and duration of droughts that affect the Mediterranean basin urges to evaluate forest vulnerability to drought and their effects for the long-term stability of these ecosystems. In this study, we explore the responses and factors that control the resilience of holm oak (Quercus ilex) woodlands to recent extreme droughts during 2000-2019, using a remote sensing approach over a broad scale climate aridity gradient that extends from sub-humid to semi-arid climate conditions over 100,000 km2 in eastern Spain. Overall, our results indicated that climate aridity and forest structure largely control the resistance, recovery and resilience of the studied holm oak woodlands to drought, which are also affected by drought intensity and both pre- and post-drought hydric conditions. We found that Q. ilex woodlands located in the dry edge of the explored climate aridity gradient showed a high sensitivity to extreme drought. Their resistance, assessed as the capacity of the woodlands to maintain primary production during drought, was low. They also showed a poor resilience, characterized by a low capacity to fully recover their pre-drought production levels. Contrarily, holm oak woodlands in sub-humid areas of the study region, where wetter climate conditions may alleviate water stress during dry periods, showed a high resistance and resilience to the effects of droughts. Drought vulnerability was particularly high for dense holm oak stands developed under semi-arid climate conditions, where strong competition for scarce water resources largely increased the negative effects of extreme drought on landscape-level ecosystem production. We also discuss the implications of these results for adaptive management of holm oak forests in the present context of climate change.
Model evaluation strategy impacts the interpretation and performance of machine learning models
Authors: Sweet Lily-belle , Müller Christoph , Anand Mohit , Zscheischler Jakob
Published: February 2023

Machine learning models are able to capture highly complex, nonlinear relationships, and have been used in recent years to accurately predict crop yields at regional and national scales. This success suggests that the use of ‘interpretable’ or ‘explainable’ machine learning (XAI) methods may facilitate improved scientific understanding of the compounding interactions between climate, crop physiology and yields. However, studies have identified implausible, contradicting or ambiguous results from the use of these methods. At the same time, researchers in fields such as ecology and remote sensing have called attention to issues with robust model evaluation on spatiotemporal datasets. This suggests that XAI methods may produce misleading results when applied to spatiotemporal datasets, but the impact of model evaluation strategy on the results of such methods has not yet been examined.In this study, machine learning models are trained to predict simulated crop yield, and the impact of model evaluation strategy on the interpretation and performance of the resulting models is assessed. Using data from a process-based crop model allows us to then comment on the plausibility of the explanations provided by common XAI methods. Our results show that the choice of evaluation strategy has an impact on (i) the interpretations of the model using common XAI methods such as permutation feature importance and (ii) the resulting model skill on unseen years and regions. We find that use of a novel cross-validation strategy based on clustering in feature-space results in the most plausible interpretations. Additionally, we find that the use of this strategy during hyperparameter tuning and feature selection results in improved model performance on unseen years and regions. Our results provide a first step towards the establishment of best practices for model evaluation strategy in similar future studies.
Enhancing global SO2 emission inventories using Sentinel-5P TROPOMI satellite data
Authors: Jost Adrian , Beirle Steffen , Borger Christian , Theys Nicolas , Ziegler Steffen , Wagner Thomas
Published: February 2023

We report a newly developed global anthropogenic SO2 emission inventory. Within this study, SO2 measurements from the Tropospheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5P satellite have been used to detect and quantify SO2 emissions from point sources for the time range 2018-2022. Our algorithm derives the advection of SO2 by combining TROPOMI SO2 column densities and wind fields from ERA5, i.e. taking the product of vertical column densities and the horizontally projected wind speed. In addition, several corrections, e.g., for satellite sensitivity and topography are applied. The results will be compared to existing emission datasets.The study is part of the World Emission project funded by ESA and the complete SO2 emission inventory will be available via the World Emission Portal at https://app.world-emission.com.
Site survey for potential MoHole drilling sites in the Guatemala Basin
Authors: Henstock Timothy , Grevemeyer Ingo , Dannowski Anke , Marjanovic Milena , Hilbert Helene-Sophie , Robinson Adam , Li Yuhan , Teagle Damon
Published: February 2023

A founding ambition of scientific ocean drilling is to drill a MoHole that penetrates the entire ocean crust and into the upper mantle at a location representative of normal crustal accretion and evolution. This remains the only way to test many of our key ideas about how new crust forms at mid-ocean ridges, cools and ages through interactions with the oceans. The technical challenges of drilling such a deep hole limit potential locations to a small number of candidate regions, which need to be sufficiently old to be cool at Moho depths but shallow enough for riser drilling.In December 2022 and January 2023 RRS James Cook expedition JC228 carried out the first site survey to collect complete seismic datasets in one of the candidate regions, the Guatemala Basin. We collected two grids and a long flowline profile of multichannel seismic reflection (MCS) data using a tuned airgun array of 5000 in3 together with a 6 km hydrophone streamer. Airgun shots were simultaneously recorded on 52 ocean-bottom seismometers (OBS) deployed at 84 locations. Shot spacings of 150 m and 75 m were optimised for the different recordings. The survey samples crust formed between 19 and 21 Ma, at present-day water depths of 3200-3400 m, and is approximately along a flowline from the existing ODP/IODP Site 1256, where intact ocean crust has been drilled to the gabbros. Initial processing of the MCS data on board the ship shows a normal incidence reflection Moho that is variable in amplitude over distances of ~10 km, but is present at the intersections of several MCS profiles. Wide-angle PmP reflections on the OBS are clear across the region. There is obvious anisotropy in the Pn upper mantle refraction on the OBS, with a strong and high-velocity arrival along the flowline, and weaker and slower arrivals in the isochron direction at each grid. Overall, the initial observations are extremely promising for identification of multiple viable Mohole drilling locations.