bluuebunny/crossref_metadata_2025 huggingface dataset:
Predicting water quality variability in a Mediterranean hypereutrophic monomictic reservoir using Sentinel-2 MSI: the importance of model functional form
Authors: Alameddine Ibrahim , Abbas Mohamad
Published: March 2021

Anthropogenic eutrophication is a pressing global environmental problem that threatens the ecological functions of many inland freshwaters and diminishes their abilities to meet their designated uses. Water authorities worldwide are being pressed to manage the negative consequences of harmful algal blooms (HABs) based largely on data collected from conventional monitoring programs that lack the needed spatio-temporal resolution for effective lake/reservoir management. This study assesses the potential of using Sentinel 2 MSI to predict and assess the spatio-temporal variability in the water quality of the Qaraoun Reservoir, a poorly-monitored Mediterranean hypereutrophic monomictic reservoir that is subject to extensive HABs during the growing season. The performance and transferability of water quality models previously calibrated based on Landsat 7 and 8 surface reflectance to predict Chlorophyll-a (Chl-a), total suspended solids (TSS), Secchi Disk Depth (SDD), and Phycocyanin (PC) levels in the reservoir are first assessed. The results showed poor transferability between Landsat and Sentinel 2, with all models experiencing a significant drop in their predictive skill. Sentinel 2 specific models were then developed for the reservoir based on 153 water quality samples collected over two years. Different model functional forms were then tested, including multiple linear regressions (MR), multivariate adaptive regression splines (MARS), and support vector regressions (SVR). Our results showed that for Chl-a, the MARS model outperformed MR and SVR, with an R2 of 60%. Meanwhile, the SVR-based models outperformed their MR and MARS counterparts for TSS, SDD and PC (R2 = 59%, 94%, and 72% respectively).
Carbon and nitrogen isotopes in grasslands of northern China
Authors: Wu Yuntao , Song Zhaoliang
Published: March 2021

Carbon (C) and nitrogen (N) isotopes are important traits to characterize terrestrial ecosystems. Studying the relationships between carbon and nitrogen isotopes of soils and plants in different grassland types and under different environmental conditions is of great importance to the reconstruction of past climate. In this study, we selected three different grassland ecosystems (temperate meadow steppe, temperate typical steppe and temperate desert steppe) in northern China, collected meteorological data and plant and soil samples, determined the basic physical and chemical properties, C and N isotopes to explore the patterns and controlling factors of C and N isotopes in plants and soils of grasslands in northern China. The results showed that there were significant differences in soil δ13C and δ15N between different grassland types in the northern temperate zone. The soil δ13C and δ15N of different depths of the northern temperate grassland soil increased with the increase of soil depth. The surface soil δ13C of temperate meadow steppe and temperate desert steppe had a good correlation with plant sample δ13C. The surface soil δ15N temperate typical steppe and temperate desert steppe had a good correlation with plant sample δ15N. Mean annual temperature (MAT) and mean annual precipitation (MAP) had a complicated relationship with carbon and nitrogen isotopes of surface soil and plant sample in northern temperate grassland. The surface soil δ13C and δ15N and the plant sample δ15N can be used as indicators of the change of MAT.

Keywords: carbon isotopes, nitrogen isotopes, grasslands, climate, soil depth
Resizing irrigation management for TWW quality with a physically-based model to preserve soil quality: A case study in Beit Dajan-Palestine
Authors: Dragonetti Giovanna , Isleem Nabeeh , Khadra Roula
Published: March 2021

Irrigation with Treated Wastewater (TWW) is a well-known and long-established agricultural practice in Palestine. Being a source of water and nutrients, long term use of TWW can lead to imbalances that affect plant development, soil, and groundwater quality. Consequently, irrigation frequency and interval should be properly scheduled, especially when Salts and Fertilizers (FS-TWW) cannot be separated from water.

Physically based models may be relevant tools to support an adequate irrigation management with TWW for a simultaneous supply of water and fertilizers assessed pursuant to the effects of TWW on soil properties and water fluxes into and out of the root zone.

The present research was conducted in the framework of Non Conventional WAter Re-use in Agriculture in MEditerranean countries (MENAWARA) ENI CBC Med project, with the aim to propose an alternative TWW irrigation management based on both water requirements and allowable thresholds of soil solution electrical conductivity (ECe), to prevent soil salinity using physically-based Hydrus-1D model.

To this purpose, a case study in Beit Dajan cultivated with citrus and irrigated with TWW was selected to determine the long term effects of TWW on the soil and on root uptake, considering a two-year (2018-2019) simulations and generating two FS-TWW irrigation scenarios: 1) non-optimized salt supply (NONOPT-FS-TWW) where irrigation volumes fully satisfied crop evapotranspiration demand: 2) optimized salt supply (OPT-FS-TWW) accounting for crop evapotranspiration and respecting allowable thresholds of soil solution electrical conductivity (ECe) by assuming an average soil salinity tolerance in the root zone.

Soil water movement, ECe, nitrate and ammonium concentrations were simulated, inputting averaged ten-yearly climate data and soil and water quality data measured at the end of each of the two considered years. The results in terms of soil salinity and root uptake impact are considered to define a proper TWW irrigation management for citrus.

The outputs of the scenario OPT-FS-TWW clearly demonstrate the reduction of soil salinity in the root zone, and of water and nutrient fluxes below 60cm, and thus an improvement of water and nutrient uptake, as compared to NON-OPT-FS-TWW scenario.

The results suggest that aligning the classical irrigation practices to TWW reuse by considering ECe as an additional variable is appropriate, allows to curb soil salinity, and ensures root water uptake of citrus, although TWW has high salinity levels that may jeopardize plant response after a sequence of irrigation events.
Global warming, slope stability, and the dynamization of geological hazards in high mountain regions: a case study from the Eastern Alps.
Authors: Savi Sara , Comiti Francesco , Strecker Manfred
Published: March 2021

In recent decades, slope instability in high-mountain regions has often been linked to the increase in temperature and the associated permafrost degradation and/or the increase in frequency/intensity of rainstorm events. In this context we analyzed the spatiotemporal evolution and potential controlling mechanisms of small to medium-size rockfalls and debris flows in a small catchment of the Italian Alps (Sulden/Solda basin). We found that rockfall events have been increasing since the 1990s, whereas debris flows have increased only since 2010. The current warming trend of mountain regions such as the Southern Alps is leading to an increased elevation of rockfall detachment areas (altitudinal shift of ca. 300-400 m in the study site), mostly controlled by frost-cracking and permafrost thawing. In contrast, the occurrence of debris flows does not exhibit such an altitudinal shift, as it is primarily driven by extreme precipitation events exceeding the 75th percentile of the intensity-duration rainfall distribution. The possible occurrence of a debris-flow event in this environment may be additionally influenced by the accumulation of unconsolidated debris over time, which is then released during extreme rainfall events. Overall, there is evidence that the upper Sulden basin (above ca. 2500 m asl), and especially the areas in the proximity of glaciers, have experienced a significant decrease in slope stability since the 1990s and that an increase in rockfalls and debris flows during spring and summer can be observed. Our study thus confirms that “forward-looking” hazard mapping should be undertaken in these increasingly frequented areas of the Alps, as these environmental changes have elevated the overall hazard level in these high-elevation regions.
Spatial and temporal variability of iodine in aerosol
Authors: Gomez Martin Juan Carlos , Saiz-Lopez Alfonso , Cuevas Carlos , Fernandez Rafael , Gilfedder Benjamin , Weller Rolf , Baker Alex , Droste Elise , Lai Senchao
Published: March 2021

In this work we describe the compilation and homogenization of an extensive dataset of aerosol total iodine field observations in the period between 1963 and 2018 and we discuss its spatial and temporal trends. Total iodine in aerosol shows a distinct latitudinal dependence, with an enhancement towards the northern hemisphere (NH) tropics and lower values towards the poles. Longitudinally, there is some indication of a wave-one profile in the Tropics, which peaks in the Atlantic and shows a minimum in the Pacific, following the well-known wave-one longitudinal variation of tropical tropospheric ozone. These spatial trends result from the global distribution of the main oceanic iodine source to the atmosphere (the reaction of surface ozone with aqueous iodide on the sea water-air interface). New data from Antarctica show that the south polar seasonal variation of iodine in aerosol mirrors that observed previously in the Arctic, with two equinoctial maxima and the dominant maximum occurring in spring. While no clear seasonal variability is observed in NH middle latitudes, there is an indication of different seasonal cycles in the NH tropical Atlantic and Pacific. A weak positive long-term trend is observed in the tropical annual averages, which is consistent with an enhancement of the anthropogenic ozone-driven global oceanic source of iodine over the last 50 years.
Estimation of future precipitation Return-Levels in Europe for the adaptation of industrial facilities
Authors: Parey Sylvie , Michelangeli Paul-Antoine
Published: March 2021

Industrial facilities, like any building or installation, are designed to withstand defined levels of natural hazards during their lifetime. These levels are requested by the regulations, and are commonly estimated by use of the Statistical Extreme Value theory ahead of the building in order to support the design of the planned asset. However, for long lasting installations, climate change may change the frequency of the level defined at the time of the building, so that the protection is not as high as initially expected. This work presented here aims at describing and testing a way to estimate Return Levels for precipitation in different locations in Europe at the 2050 time horizon. The methodology is based on the definition of a variable whose extremes can be considered as stationary, so that future Return Levels are obtained from those of this variable and the climate model changes in mean, standard deviation and rainy day frequency at the desired future horizon (Acero et al. 2017). The methodology is first tested in a cross-validation setting over the historical period using 15 rainfall observation time series in Europe provided by the ECA&D dataset and CMIP5 climate model simulations. Then, estimates of the 50-year Return Levels in 2050 are computed. The methodology is then applied to the gridded E-OBS dataset with the objective of producing risk maps at the European scale. The first step is then to compare the estimations previously obtained for the station time series to those obtained for the nearest E-OBS grid points, in order to assess the ability of gridded data to faithfully represent the behavior of the extremes. Depending on the results, advices can be given about the most suited way to map future rainfall extremes in Europe in relation to the adaptation of industrial facilities.

 

Reference:

Acero F.J., Parey S., Hoang T.T.H., Dacunha-Castelle D., Garcia J.A. and Gallego M.C.: Non-stationary future Return Levels for extreme rainfall over Extremadura (SW Iberian Peninsula). Hydrological Sciences Journal, 2017, DOI: 10.1080/02626667.2017.1328559
The impact of iron distribution among cloud droplets or aqueous aerosol particles on multiphase oxidant levels
Authors: Khaled Amina , Zhang Minghui , Ervens Barbara
Published: March 2021

Reactive oxygen species (ROS), such as hydroxyl radical (OH•), hydroperoxy radicals (HO2•/O2-), and hydrogen peroxide (H2O2), are produced in cloud droplets and aqueous aerosol. Multiphase model studies suggest that the Fenton reaction, i.e. the oxidation of Fe(II) by H2O2 represents one of the main sources of the OH radical in the aqueous phase.

Current cloud and aerosol multiphase chemistry models are usually initialized with equal iron concentrations in all droplets or particles as derived from bulk samples of cloud water or aerosol composition. However, analysis of single aerosol particles has revealed that only a small number fraction of particles and, thus, of cloud droplets contain iron.

The aim of our study is to identify the impacts of the iron distribution in cloud droplets or aqueous aerosol particles on the total (gas + aqueous) budgets of OH, HO2, H2O2 and O3 in the multiphase system.

By means of model studies, we compare predicted oxidant budgets based on the assumptions of iron distributed among all droplets or particles versus the same iron mass concentrated in a few droplets (or particles) in the total population only. Our results suggest that the traditional approach based on bulk iron concentrations may significantly underestimate total OH budgets, whereas the predicted levels of H2O2, HO2/O2- and ozone are less affected. The reasons for the different findings between (i) the various oxidants and (ii) cloud droplets vs aerosol particles will be discussed. In summary, our model studies suggest that oxidant levels and oxidation potentials of particulate matter in the atmosphere can only be accurately assessed if particle- and size-resolved aerosol composition is accounted for.
Clogging and un-clogging of the subduction plumbing system may generate tremor-like patterns
Authors: Farge Gaspard , Jaupart Claude , Shapiro Nikolaï
Published: March 2021

Many subduction zones host intermittent, low-frequency, low-magnitude seismic activity emitted from the vicinity of the plates' interface. For instance, in Guerrero, Mexico, deep (30--50 km) low-frequency earthquakes (LFEs) occur in bursts, and migrate in cascades along the subduction interface. Those patterns are often attributed to episodic pulses of fluid pressure and slow slip that travel within the fault zone. However, the dynamic behavior of the permeable system in which fluid-pressure circulates remains a blindspot in most models of tremor generation, even as geological observations report pervasive imprint of strong, localized fluid pressure and permeability variations in its source region.

In order to analyze the role of such processes in generating tremor, we design a simple model of how fluid pressure and permeability can interact within the subduction interface, and generate realistic, tremor-like patterns. It is based on seismic source triggering and interaction in a permeable channel. The latter contains a number of low-permeability plugs acting as elementary fault-valves. In a mechanism akin to erosive burst documented in porous media, valve permeability abruptly opens and closes in response to the local fluid pressure. The brutal pressure transient and/or mechanical fracturing associated with valve opening acts as the seismic source of an LFE-like event. The strong fluid pressure transient that it triggers allows valves to interact constructively: as a valve breaks open, neighbor valves are more likely to break. This interaction therefore leads to cascades and migrations of synthetic seismicity along the model fault channel, that can synchronize into larger bursts of activity that migrate more slowly along the channel. In our model, valve activity draws patterns of that closely resemble tremor patterns in Guerrero and other subduction zones.

The input metamorphic fluid flux at the base of the channel exerts a key control on the occurence of and distribution of synthetic tremor in space and time. A weak input flux will not allow valves to open, conversely a strong flux will not allow them to close. In both cases, no activity will occur. However when the value of the fluid flux is intermediate, permanent regimes of sustained activity arise. Depending on its value, activity can be strongly time-clustered, quasi-periodic or random but constant in time.

Our model is based on a simple yet powerful and realistic description of the permeability and its dynamics in fault zones. It allows for new interpretations of low-frequency seismicity in terms of effective flux and fault-zone permeability, both for long-term regimes and finer scale, transient dynamics. Eventually, it could lead to deep enhancements of our understanding of fault-zone hydraulic processes and how they are coupled with fault-slip.
On the way to realistic large eddy simulations – A comparison of virtual measurements with CHEESEHEAD19 field measurements
Authors: Wanner Luise , Paleri Sreenath , Speidel Johannes , Desai Ankur , Sühring Matthias , Vogelmann Hannes , Wagner Timothy , Oncley Steven , Brown William , Mauder Matthias
Published: March 2021

Large-eddy simulations are useful tools to study transport processes by mesoscale structures in the atmospheric boundary layer, since in contrast to single-tower eddy covariance measurements, they provide not only temporally but also spatially highly resolved information. Therefore, they are well suited to study the energy balance closure problem, for which the mesoscale transport of latent and sensible heat, triggered by heterogeneous ecosystems, is suspected to be a major cause. However, this requires simulations that are as realistic as possible and thus allow a comparison of real measurements in the field and virtual measurements in the simulation.
During the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors (CHEESEHEAD) experiment in the summer of 2019, a heterogeneous 10x10 square km domain was intensively sampled across scales. This data offers a unique possibility to set up large-eddy simulations with realistic surface heterogeneity. We use PALM to simulate two days and an area of 40 by 40 square kilometers incorporating the CHEESEHEAD site. The large scale atmospheric forcings to inform the boundary conditions are determined from the NCEP HRRR product. As the lower boundary condition, we use a soil and land-surface model coupled with a plant-canopy model, which we adapt to the CHEESEHEAD area based on ground-based and airborne measurements of plant physiological data.
In this study, we investigate how well the simulations match with real measurements by comparing simulated profiles and virtual tower measurements with field measurements from radiosonde ascents, lidar measurements of three-dimensional wind and water vapor, eddy-covariance measurements from the 400 meter tower in the center of the study domain, as well as from typical eddy-covariance stations distributed through the study area. This way, we investigate how realistic the simulations actually are and to what extent the knowledge gained from them concerning the energy balance closure problem can be transferred to field measurements.
Decadal variability of the East Asian summer jet and its relationship to sea surface temperatures
Authors: Patterson Matthew , Woollings Tim , O'Reilly Chris , Weisheimer Antje
Published: March 2021

Variability of the East Asian summer jet stream (EAJ) has a significant impact on the climate of East Asia, primarily through its modulation of East Asian precipitation. In recent decades the impact of sea surface temperatures (SSTs) in the tropical Indian and Pacific oceans on the EAJ have been studied in considerable detail, however much less is known about the drivers of EAJ variability on decadal or multi-decadal timescales. Investigating this problem is made more challenging by the temporal limitations of reanalysis datasets.

In order to establish whether SSTs can provide a source of skill in predicting decadal variations of the EAJ, we analyse long pre-industrial control runs of the CMIP6 models. One issue with studying coupled model runs is that it is often unclear whether particular SST anomalies are forcing the atmosphere, and thus can provide a meaningful source of skill, or whether they are merely responding to local atmospheric anomalies. We address this issue by combining SST and turbulent heat flux information to indicate the direction of the forcing.
Width control on event scale bedload dynamics in bedrock-confined channels
Authors: Cook Kristen , Turowski Jens , Hovius Niels
Published: March 2021

In mixed bedrock-alluvial rivers, the response of the system to a flood event can be affected by a number of factors, including coarse sediment availability in the channel, sediment supply from the hillslopes and upstream, flood sequencing, and coarse sediment grain size distribution. However, the impact of along-stream changes in channel width on bedload transport dynamics remains largely unexplored. We combine field data, theory, and numerical modeling to address this gap. Observations from two flood events in the Daan River gorge in western Taiwan suggest that coarse sediment evacuation and re-deposition can cause intra-flood changes of up to several meters in channel bed elevation that are distinct from measured before/after bed changes. We hypothesize that this could be related to the abrupt change in width between the 1 km long bedrock gorge and the river upstream and downstream. An analysis of the theoretical relationships between discharge, channel width, and bedload transport capacity shows that for a given slope, narrow channels transport bedload more efficiently than wide ones at low discharges, while wider channels are more efficient at high discharges. We used the model sedFlow to explore this effect, running a random sequence of floods through a channel with a narrow gorge section bounded upstream and downstream by wider reaches. Channel response to imposed floods is complex, as high and low discharges drive different spatial patterns of erosion and deposition, and the channel may experience both of these regimes during the peak and recession periods of each flood. Our modeling suggests that width differences alone can drive substantial variations in sediment flux and bed response, without the need for variations in sediment supply or mobility. Further, the deposition or erosion that takes place within a flood is often not reflected in the before/after changes to the bed, and this disconnect increases with increasing flood size.
Rapid morphological evolution during beach breaching and closure at a bar-built estuary
Authors: Orescanin Mara , McPherson Tyonna , Jessen Paul
Published: March 2021

The Carmel River runs 58 km from the Santa Lucia Mountains through the Carmel Valley eventually entering a lagoon at Carmel River State Beach near Carmel, California, USA. During the dry summer months, the lagoon is closed, with no connection to the coastal ocean.  However, during the wet winter months, the river often breaches through the lagoon allowing water to freely flow between the river and Carmel Bay. Sediment transport, in part owing to river discharge and in part owing to ocean forcing (tides and waves), contributes heavily to whether the lagoon is open or closed: when there are low flow conditions, waves and tides can decrease flow rates in the breach, allowing sediment to settle. The sediment budget is expected to be a closed system, owing to the rocky headlands and long-term stability (no yearly regression or transgression) of the shoreline, despite managed attempts to control breach and closure timing. However, it is currently unknown 1) how velocity profiles evolve during breaching, and 2) how much sediment moves during such an event. The hypothesis is that the breach mouth can completely disappear and re-emerge over a single breach-closure cycle, leading to meter-scale daily accretion and erosion rates of berm height if berm elevation is significantly lower than the expected steady-state berm height. Furthermore, it is hypothesized that during active breaching, discharge rates through the breach channel are larger than upstream river discharge rates owing to elevated water levels within the back lagoon. This study uses a RiverSurveyor M9 Acoustic Doppler Profiler to measure outflow discharge and GPS topographic surveys to quantify elevation changes. A velocity profile can be built which will estimate the sediment transport potential within the breach. The information obtained will help identify and better understand the river discharge thresholds which contribute to frequent breaching as well as estimates of morphological evolution during breaching, which are currently unknown, and can assist in determining likelihood of successful managed breaching and closure events. 
The Influence of Vapor Attachment Kinetics on Snow Effective Properties
Authors: Fourteau Kevin , Domine Florent , Hagenmuller Pascal
Published: March 2021

Proper modelling of heat and mass transfer in snow is a prerequisite for understanding snow metamorphism and simulating the mass and energy budget of a snowpack and the underlying ground. The transfer of heat and water vapor in snow can be described with macroscopic conservation equations, which include effective coefficients such as the snow thermal conductivity or the snow water vapor diffusion coefficient. Here, we investigate the impact of the surface kinetics of water vapor sublimation and deposition at the microscopic scale on these macroscopic equations, restraining ourselves to the limiting cases of slow and fast kinetics. In particular, we show that under the assumption of fast kinetics the thermal behavior of snow is similar to that of a regular inert medium, but with an enhanced conduction in the pores, due to latent heat transported with water vapor. Besides, faster kinetics increases the effective water vapor diffusion coefficient, which nonetheless remains less than that in free air. Most (but not all) available experimental investigations suggest that in snow, fast surface kinetics prevails, so that our results have numerous implications for the proper simulation of heat and mass transfer in snow.
Hydrological variability and suspended particulate matter in the middle river Niger bassin
Authors: Boubacar Moussa Moussa , Abdourhamane Touré Amadou , Lartiges Bruno , Rochelle Newall Emma , Kergoat Laurent , Robert Elodie , Gosset Marielle , Alkali Tanimoun Bachir , Grippa Manuela
Published: March 2021

In the Sahel, climate variability and high population growth have led to changes in surface conditions that resulted in increased runoff coefficients and discharge in the major Sahelian rivers. The mid reaches of the Niger river have experienced significant increases in the Red flood, or local flood, that occurs during the rainy season between June and September, relative to Black flood, or Guinean flood that arrives in Niamey from December onwards.
The objective of this work was to characterize suspended particulate matter (SPM) during the Red and Black floods in the Niamey area and analyse their spatio-temporal dynamics. Two approaches are used : the first one consists of regular in-situ measurements of SPM concentration and in their physical and mineral characterization by electron microscopy; the second is based on monitoring water color by both in-situ and satellite (Sentinel 2) radiometric measurements.
SPM are characterized by very fine particles (with a major mode around 0.1-0.2 micrometers) mainly composed by kaolinites (iron oxides are also observed during the Red flood). This, combined with the very high levels of SPM concentration reached during the rainy season, results in very high values of reflectance in the visible end infrared bands. Radiometric measurements in the nir band by both the in-situ SKYE sensor and the Sentinel2 sensor are found to be significantly correlated to in-situ SPM, allowing efficient monitoring of SPM concentration in time and space.
SPM-discharge curves, reveal a complex relationship : SPM increases very rapidly at the beginning of the rainy season when soils are washed out after the long dry period, reaching a peak before the first discharge peak (Red flood). SPM continues to decrease during the second discharge peak (Black flood) from December to February, providing a distinct and unique signature. Analysis of satellite data allowed identifying the main sources of SPM and to quantify the significant contribution of the right bank river tributaries to sediments in the middle Niger river bassin. This contribution may further increase in the context of global changes (climate and anthropogenic) with important consequences on sediment transport but also on water quality and bacterial concentration which are strongly influenced by high SPM.
Spatial patterns of argan-tree influence on soil quality of intertree areas in open woodlands in South Morocco
Authors: Kirchhoff Mario , Romes Tobias , Marzolff Irene , Seeger Manuel , Aït Hssaine Ali , Ries Johannes B.
Published: March 2021

The endemic argan tree (Argania spinosa) in Morocco, which is the source of the valuable argan oil, forms open-canopy forests that are highly degraded due to overgrazing, illegal cutting of firewood and the expanding intensive agriculture. Because of the high grazing pressure young sprouts cannot establish themselves, reforestation measures are often unsuccessful and the bare areas between the isolated trees are expanding. In a previous study, we could already show that these intertree areas are more degraded than the areas under the trees, regarding various soil parameters as well as their erodibility and infiltration capacity.

The spatial extent of argan trees on soil quality from the trunk to the intertree area is so far unknown. Hypothetically, the tree influences the soil of the intertree area by wind drift of tree litter and soil material towards the East, i.e. main wind direction, and downhill by runoff and erosion processes of soil material downslope. Tree shadow in the hot midday and afternoon sun should have positive influences on soil moisture in northern or northeastern directions. To test this hypothesis, we took 424 soil samples around 31 argan trees in four directions, uphill, downhill and in both directions parallel to the slope towards the nearest neighbouring tree in that direction. Samples along these transects were taken near the trunk, just inside and just outside the area covered by the tree crown and in the intertree area in the middle between two trees. The soil samples were analysed for various soil parameters (C/N, percolation stability, electrical conductivity, pH, soil moisture).

The first results show that the influence of the trees is not limited to the crown-covered area but for some trees extends further into the intertree area in specific directions according to the hypothesis (East due to wind drift, North due to shade and downslope due to slope runoff). For other trees the influence of the trees does not even encompass the whole crown-covered area, where we found similarly lower soil quality as for the bare intertree areas. These differences may result from the degradation state of the tree as well as from the different characteristics of the study areas. Understanding the way argan trees influence their surrounding intertree areas would enable structured reforestation measures with a higher chance of successful rejuvenation of the argan forest.
Definition of 3D rainfall thresholds for operative LEWS
Authors: Rosi Ascanio , Monni Antonio , Gallucci Angela , Casagli Nicola
Published: March 2021

Rainfall induced landslide is one of the most common hazards worldwide and it is responsible every year of huge losses, both economic and social. 
Because of the high impact of this kind of natural hazard, the forecasting of the meteorological condition associated with the initiation of landslide has become paramount in the recent years and several papers addressing this issue have been published.
When working over large areas, the definition of rainfall thresholds is the most used approach, since it requires few data that can be easily retrieved: landslide triggering date and location and rainfall recording associated to landslide events.
The intensity-duration threshold is the most used approach and it showed over the time its potential to be implemented in an operative landslide early warning system (LEWS), but literature papers showed that this approach is affected by a main drawback, i.e., the high number of false positives (events that are not capable of triggering landslides are classified as landslide triggering events).
To overcome this problem several authors tried to combine these thresholds with other parameters and recently one of the most promising approach is the use of the antecedent soil moisture condition, but this parameter is note very easily available for large areas and it is difficult to retrieve it in real time, so as it can be used in a LEWS.
In our work we used antecedent rainfall to simulate the progressive saturation of the soil and then the soil moisture condition associated with the initiation of landslides.
In a given area the total rainfall recorded by each rain gauge over a defined period of time prior the landslide is considered and used to define a parameter named MeAR (Mean Antecedent Rainfall), which represent the mean rainfall of the area over a given time interval, as recorded by all the active rain gauges.
The MeAR parameter has been coupled with classical I-D thresholds to define 3D thresholds, where the conditions associated with the initiation of a landslide are defined by a portion of a 3D space, instead of a portion of a 2D plane. This approach has been tested in Emilia-Romagna region (Italy) and it resulted the possibility of reducing false positives from 30% up to 80% on different areas.
On the effective resolution of WRF simulations at microscale grid resolution.
Authors: Bolgiani Pedro , Díaz-Fernández Javier , Quitián-Hernández Lara , Sastre Mariano , Santos-Muñoz Daniel , Farrán José Ignacio , González-Alemán Juan Jesús , Valero Francisco , Martín María Luisa
Published: March 2021

As the computational capacity has been largely improved in the last decades, the grid configuration of numerical weather prediction models has stepped into microscale resolutions. Even if mesoscale models are not originally designed to reproduce fine scale phenomena, a large effort is being made by the research community to improve and adapt these systems. However, reasonable doubts exist regarding the ability of the models to forecast this type of events, due to the unfit parametrizations and the appearance of instabilities and lack of sensitivity in the variables. Here, the Weather Research and Forecasting (WRF) model effective resolution is evaluated for several situations and grid resolutions. This is achieved by assessing the curve of dissipation for the wind kinetic energy. Results show that the simulated energy spectrum responds to different synoptic conditions. Nevertheless, when the model is forced into microscale grid resolutions the dissipation curves present an unrealistic atmospheric energy. This may be a partial explanation to the aforementioned issues and imposes a large uncertainty to forecasting at these resolutions.
Shallow deformation kinematic history, a new insight from carbonates U-Pb direct dating by LA-ICP-MS imaging technique.
Authors: Monchal Vincent , Drost Kerstin , Chew David
Published: March 2021

This project aims to refine direct dating of carbonates by the U-Pb system, using a new LA-ICP-MS imaging technique that incorporates complementary element and textural analysis information. The direct dating of carbonates in deep time has been considered desirable for decades (e.g. Jahn and Cuvellier, 1994) given their ubiquity in the Earth system, and carbonates are a key phase for dating geological processes such as brittle-ductile deformation in carbonate successions. This new method facilitates detailed (on the scale of tens of microns) mapping of U-Pb isotope and element distributions (cf Drost et al., 2018), and is here applied to carbonate vein dating to constrain local and regional histories of deformation or fluid activity.

In this presentation we focus on a sample from the Carboniferous North Dublin Basin, Ireland. The basin has been affected by deformation that led to tight chevron folds and kinematically-linked dextral en-echelon vein sets. Additionally bedding-parallel veins and  slickenfibres are common. The deformation has been conventionally assumed to be of Variscan age, and some Variscan U-Pb ages are recorded in this study. However many calcites analysed yield late Eocene ages, a deformation phase that is hitherto undetected on the Irish mainland. Our data indicate repeated fault slip over a peroid of at least c. 4 my during late Eocene times and, thus, demonstrate the ability of the LA-ICP-MS imaging approach to not only unravel complex polyphase deformation histories in carbonates but also to resolve processes on fine temporal and spatial scales.

 

 

DROST, K., CHEW, D., PETRUS, J. A., SCHOLZE, F., WOODHEAD, J. D., SCHNEIDER, J. W. & HARPER, D. A. T. 2018. An Image Mapping Approach to U-Pb LA-ICP-MS Carbonate Dating and Applications to Direct Dating of Carbonate Sedimentation. Geochemistry, Geophysics, Geosystems, 19, 4631-4648.

JAHN, B.-M. & CUVELLIER, H. 1994. Pb-Pb and U-Pb geochronology of carbonate rocks: an assessment. Chemical Geology, 115, 125-151.
Stability analysis of the surrounding rock of cavern under extreme situation based on limited borehole data.
Authors: Tan Long , Xiang Wei
Published: March 2021

In the pre-feasibility study stage, only a small amount of borehole data can be obtained. Since the available geological information is insufficient, the engineering geological conditions of the project can only be preliminarily and approximately estimated during this stage. In this study, we attempt to seek a method to make a preliminary analysis and evaluation of the stability of the surrounding rock masses of an underground rock carven project, which makes full and optimum use of the limited borehole data to accomplish the assessment of the investigated site. The basic information on rock fractures is extracted from the borehole Television logging data and the fracture extension directions are also determined. Providing that the cracks detected in the borehole would extend to the cavern area, the cracks with appropriate direction, larger width and larger hydraulic conductivity can be selected. These selected cracks are considered in the numerical model established using ANSYS, and the stability of surrounding rock of cavern is analyzed under this situation. In the absence of large amount of borehole data, this method, which set up an extreme case, can be used to analyze possible failure of rock mass under extreme adverse conduction in advance. In general, the proposed method for stability analysis could contribute to the design and construction practice of a tunnel project constructed in fractured rock masses.
Ultra-short-term prediction of LOD using LSTM neural networks
Authors: Gou Junyang , Kiani Shahvandi Mostafa , Hohensinn Roland , Soja Benedikt
Published: March 2021

The Earth Orientation Parameters (EOP) are fundamentals of geodesy, connecting the terrestrial and celestial reference frames. The typical way to generate EOP of highest accuracy is combining different space geodetic techniques. Due to the time demand for processing data and combining different techniques, the combined EOP products often have latencies from several days to several weeks. However, real-time EOP are needed for multiple geodetic and geophysical applications, including precise navigation and operation of satellites. Predictions of EOP in ultra-short time can overcome the problem of latency of EOP products to a certain extent.

In 2010, the Earth Orientation Parameters Prediction Comparison Campaign (EOP PCC) collected predictions from 20 methods, which were mainly based on statistical approaches, and provided a combined solution. In recent years, more hybrid and machine learning methods have been introduced for EOP prediction.

The rapid expansion of computing power and data volume in recent years has made the application of deep learning in geodesy increasingly promising. In particular, the Long Short-Term Memory (LSTM) network, one of the most popular variations of Recurrent Neural Network (RNN), is promising for geodetic time series prediction. Thanks to the special structure of its cells, LSTM network can capture the non-linear structure between different time epochs in the time series. Therefore, it is suitable for EOP prediction problems.

In this study, we investigate the potential of using LSTM for the prediction of Length of Day (LOD). The LOD data from a combination of space geodetic techniques are first preprocessed in order to obtain residuals. For this step, we experiment with the application of Savitzky-Golay filters, Singular Spectrum Analysis and the Gauss Markov model. We then employ LSTM networks of different architectures and its variations such as bidirectional LSTM networks to predict the LOD residuals in ultra-short time. Furthermore, we study the impact of Atmospheric Angular Momentum (AAM) and its forecast data on the predictions. The performance of this method is compared with other results of EOP PCC in a hindcast experiment under the same conditions. In addition, we assess the performance of LOD predictions using longer time series than for the EOP PCC to consider improvements of EOP products over the last decade.
How do synoptic conditions affect Liquid Water Path over the sea-ice-free Arctic Ocean during ACLOUD?
Authors: Kliesch Leif-Leonard , Ruiz Donoso Elena , Kulla Birte , Lauer Melanie , Mech Mario , Risse Nils , Schemann Vera , Wendisch Manfred , Crewell Susanne
Published: March 2021

Despite the strong influence of cloud liquid water on the radiative budget, the knowledge of its amount and variability in the Arctic is rather limited. The Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign took place from May 22 to June 28, 2017 and offers the possibility to investigate the Liquid Water Path (LWP) during various environmental conditions. In this period synoptic conditions were characterized as a cold air outbreak, warm air advection resulting in a period of warm conditions, and a normal period with conditions in between the cold and warm period. Deployed on the research aircraft Polar 5, the Microwave Radar/radiometer for Arctic Clouds (MiRAC) collected downward observations of radar reflectivity and Brightness Temperatures (Tb) over sea-ice-free ocean from aircraft altitudes above 2.8 km. From Tb a unique high-resolution data set of cloud LWP over remote sea-ice-free Arctic ocean is retrieved. The airborne microwave retrieved LWP is compared with LWP retrieved from visible/near-infrared techniques taken on board the aircraft as well as with two different satellite products. The respective uncertainties and the agreement among the different techniques are discussed.  

The different cloud situations observed during the three ACLOUD periods are investigated to identify differences in LWP distribution from the airborne measurements. To analyze the representativity of the limitation to specific flight tracks, continuous ground-based observations at Ny-Ålesund, ERA5 reanalysis, and simulations with the ICON model are used. While in general the airborne sampling seems to be representative for the larger region systematic difference in LWP amount between the different products occurs which will be discussed in this presentation.
The Lifecycle and Physical Drivers of Heatwaves in a Hierarchy of Model Simulations  
Authors: Jiménez-Esteve Bernat , Domeisen Daniela I.V.
Published: March 2021

Heatwaves are extreme weather events characterized by extreme near-surface temperature anomalies that persist for several days, which lead to catastrophic impacts on natural ecosystems, agriculture, human health, and economies. Different physical processes can contribute to the increase in temperature associated with heatwaves. Previous studies have shown that adiabatic compression due to subsidence and local land-atmosphere coupling are important drivers of summer heatwaves. However, less is known about the respective roles of these processes for heat extremes occurring in different seasons and latitudes.

By analyzing the different terms of the temperature tendency equation, we quantify the relative importance of horizontal wind advection, adiabatic, and diabatic processes (including radiation and surface fluxes) during the lifecycle of realistic and idealized heatwaves. We identify heatwaves both in reanalysis and in simulations using the ICOsahedral Nonhydrostatic (ICON) climate model. These simulations range from a simple zonally symmetric temperature relaxation and dry dynamics to a simulation using full physics, with coupled land and sea surface temperature forcing. This step-wise inclusion of physical processes and increasing model complexity allows us to identify the key drivers of extreme warm events and the characteristics of these across the different model complexities. In the simplest model configuration, i.e. only dry dynamics and no surface coupling, extreme temperature events are generally shorter but produce more intense temperature anomalies in the midlatitudes, where the horizontal temperature gradient is strongest. These idealized heatwaves are almost entirely driven by a very strong advection of warm air from more equatorward locations and are linked to local amplification of Rossby wave packets and atmospheric blocking. In contrast, in the complex model configuration as well as in reanalysis, summer heatwaves over land areas are mainly driven by adiabatic and diabatic processes, while advection is of secondary importance. On the other hand, extreme warm periods during winter are mainly driven by advection both in the model and reanalysis. Identifying the most relevant processes driving heatwaves can potentially benefit the prediction and representation of extreme events in operational weather and climate forecasts.
Cenozoic relative movements of Greenland and North America by closure of the North Atlantic – Arctic plate circuit
Authors: Causer Annabel , Eagles Graeme , Pérez-Díaz Lucía , Adam Jürgen
Published: March 2021

Models of Cenozoic plate motions between Greenland and North America often use magnetic anomalies in the Labrador Sea and Baffin Bay regions. The crustal origin of some of the older magnetic signatures, (pre C24, Paleocene) is questioned, and these models often portray Paleogene motions inconsistent with geological data from Nares Strait region. We test for a connection between the (mis)interpretation of anomalies and inconsistencies between model predictions and geological evidence by constructing a regional model that is not based on magnetic data in the Labrador Sea region. We do this by closing the North America – Greenland – Eurasian plate circuit from the Paleocene to Eocene – Oligocene Boundary (C25 – C13). Our findings show seafloor spreading in the Labrador Sea initiated during Eocene, and not Paleocene, times. In turn, we argue that C24 and older isochrons in the Labrador Sea are not suitable as isochron markers for modelling plate motions. We further show that the previously noted counterclockwise rotation of Greenland, marking the beginning of plate convergence in the eastern Canadian Arctic, is not a result of changes in seafloor spreading direction, but instead of the initiation of seafloor spreading in the Labrador Sea. Our model shows ~160km of shortening in the Eastern Canadian Arctic.