bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical approach to improve Radon-222 long-range atmospheric transport modelling
Authors: Quérel Arnaud , Meddouni Khadija , Quélo Denis , Doursout Thierry , Chuzel Sonia
Published: March 2021

The IRSN operates a framework capable of modelling the occurrence of gamma dose rate peaks due to Radon-222 progeny scavenged by precipitations. This framework includes a Radon-222 exhalation flux and meteorological data as inputs to a long range atmospheric transport model (ldx), and specific post-processes for reporting or performance analysis. Ldx is used in nuclear emergency preparedness and response, and it is applied to Radon-222 and its progeny to simulate both their air concentration and deposition onto the ground. This framework is successful at forecasting, in timing and intensity, around half of the peaks actually observed by the IRSN radiation monitoring stations over France. Understanding and analysing the failures is the starting point to improve the modelling.

For a statistical evaluation of the framework performance, we confronted its results to observations of gamma dose rates over a period of six months gathering more than 12,000 peaks. We used two sets of metrics to assess the agreement between model and observations: punctually (peak by peak) and continuously (whole six months’ time series of gamma dose rate and air concentration). We also performed statistical significance tests to identify the influence of some input parameters on the results.

We found that considering a factor 5 instead of a factor 2 between observed and simulated peak values increases the percentage of successfully forecasted peaks from around 50% to above 90%, whereas increasing the permissible time lag between the two has no such effect. Overall, the model shows better recall than precision: i.e. a tendency to produce more false positives than false negatives. ANOVA tests did not point out any performance difference across factors such as land cover or time of the day. Using weather radar measurements for precipitation instead of meteorological model data also improves the reanalysis performances.

This statistical evaluation serves as a gauge to measure the benefits expected from future developments of our current framework, and by that way the future evolutions of our long range module and methodology of use in case of an emergency response, and helps to determine the relevance of alternative simulation options regarding key parameters or processes, such as exhalation and soil moisture. A well-validated framework is of interest as to assess outdoor concentrations of Radon-222.
Investigation of X-band backscattering from wave breaking in a laboratory experiment
Authors: Rusakov Nikita , Baidakov Georgy , Poplavsky Evgeny , Troitskaya Yuliya , Vdovin Maksim
Published: March 2021

The work is concerned with the study of the breaking surface wave effect on the intensity and spectral characteristics of a scattered radar signal in laboratory conditions.

The experiments were carried out on the reconstructed TSWiWaT wind wave flume of the IAP RAS. The channel is 12 m long, the channel cross-section varies from 0.7 x 0.7 m at the entrance to 0.7 x 0.9 m in the working section at a distance of 9 m. The airflow speed on the axis is 3-35 m/s, which corresponds to the values of the wind speed U10 of 11-50 m/s.

The wave characteristics in the flume were measured by an array of three wave gauges positioned in the corners of an equal-side triangle with 2.5 cm side, the data sampling rate was 200 Hz. Such a system gives the opportunity to retrieve 3D frequency-wave number spectra of surface waves.

The airflow parameters were measured using the profiling method. The velocity profiles were measured in the working section using an S-shaped Pitot tube. Microwave measurements were carried out using an X-band coherent Doppler scatterometer with a wavelength of 3.2 cm with sequential reception of linear polarizations.  The absolute value of the radar cross-section (RCS) on the wavy water surface was determined by comparing the scattered signal with the signal reflected from the calibrator with a known value of the RCS - a metal ball with a diameter of 6 cm. The dimensions of the observation cross-section were 40 cm x 40 cm, the incidence angles were 30°, 40°, 50° for the upwind direction, the distance to the target was 3.15 m.

Two series of experiments were carried out. In the first case, wind waves on the surface of pure deep water, developing under the action of a fan generated wind, were studied. In the second case, a train of three waves was generated at the beginning of the channel, with the fan turned on, in order to simulate shallow water an inclined plate was placed under water in front of the measurement area. As a result, the breaking waves occurred at a fixed point and at weaker winds compared to the first case.

As a result, an increase in the scattered signal intensity during artificial wave breaking in the case of weak winds was noted. For strong winds, the effect turned out to be insignificant, despite the increased amplitude of the waves under study. The Doppler spectra analysis is also presented.

This work was supported by the RFBR projects No. 19-05-00249, 19-05-00366.  
Simulating the synergy of microwave radiometer and differential absorption radar for advancing water vapor profiling in cloudy trade-wind conditions
Authors: Schnitt Sabrina , Löhnert Ulrich , Preusker René
Published: March 2021

Continuous, high vertical resolution water vapor profile measurements are key for advancing the understanding of how clouds interact with their environment through convection, precipitation and circulation processes.  Yet, current ground-based observation systems are limited by low temporal resolution in the case of soundings, signal saturation at cloud base in the case of optical sensors, or too coarse vertical resolution in the case of passive microwave measurements. Overcoming the limitations of each single sensor, we assess the synergistic benefits of combining ground-based microwave radiometer (MWR) and the novel Differential Absorption Radar technique, based on synthetic measurements generated for typical trade wind conditions as observed during the EUREC4A field study.

Based on the single and multiple cloud layer conditions observed at Barbados Cloud Observatory, we use the passive and active microwave transfer model PAMTRA to generate synthetic measurements of the K-band MWR channels, as well as for a G-band dual-frequency radar instrument operating at frequencies of 167 and 174.8 GHz.  The synthetic brightness temperatures and radar dual-frequency ratios are combined in an optimal estimation framework to retrieve the absolute humidity profile. Varying the observation vector setup, the synergy benefits are assessed by comparing the synergistic information content (Degrees of Freedom for Signal, DFS) and retrieval errors to the respective single-instrument configuration, and by evaluating the retrieved profile using the initial sounding profile.

In single-cloud conditions, the total synergistic retrieval information content increases by more than one DFS compared to a MWR-only retrieval. While the radar measurements dominate the retrieval below and throughout the cloud layer, the MWR drives the retrieval above the cloud layer. The synergy further enhances the information content above the cloud layer by up to 15% compared to the MWR-only retrieval, accompanied by decreased retrieval errors of up to 10%. Cases of a shallow cloud layer topped by a stratiform outflow confirm the identified patterns. The radar measurements further increase the information content between the cloud layers by up to 25%. In this case, the results suggest an improved partitioning of the water vapor amount below and above the trade inversion. 

Current G-band radar signal attenuation in moist tropical conditions are expected to reduce the feasible synergy potential in a real application. Yet, increased radar signal sensitivities, adjusted frequency pairs, or drier atmospheric conditions motivate the application of this synergy concept to real measurements for advancing ground-based water vapor profiling in cloudy conditions.
High-resolution stable isotope signature of a land-falling Atmospheric River in southern Norway
Authors: Yongbiao Weng , Johannessen Aina , Sodemann Harald
Published: March 2021

Heavy precipitation at the west coast of Norway is often connected to high integrated water vapour transport within Atmospheric Rivers (AR). Here we present high-resolution measurements of stable isotopes in near-surface water vapour and precipitation during a land-falling AR event in southwestern Norway on 07 December 2016. We analyze the influences of moisture sources, weather system characteristics, and post-condensation processes on the isotopic signal in near-surface water vapour and precipitation.

During the 24-h sampling period, a total of 71 precipitation samples were collected, sampled at intervals of 10-20 min. The isotope composition of near-surface vapour was continuously monitored with a cavity ring-down spectrometer. In addition, local meteorological conditions were monitored from a vertical pointing rain radar, a laser disdrometer, and automatic weather stations.

During the event, we observe a "W"-shaped evolution of the stable isotope composition. Combining isotopic and meteorological observations, we define four different stages of the event. The two most depletion periods in the isotope δ values are associated with frontal transitions, namely a combination of two warm fronts that follow each other within a few hours, and an upper-level cold front. The d-excess shows a single maximum, and a step-wise decline in precipitation and a gradual decrease in near-surface vapour. Thereby, isotopic evolution of the near-surface vapour closely follows the precipitation with a time delay of about 30 min, except for the first stage of the event. Analysis using an isotopic below-cloud exchange model shows that the initial period of low and even negative d-excess in precipitation was most likely caused by evaporation below cloud base. At the ground, a near-constant signal representative of the airmass above is only reached after transition periods of several hours. For these steady periods, the moisture source conditions are partly reflected in the surface precipitation.

Based on our observations, we revisit the interpretation of precipitation isotope measurements during AR events in previous studies. Given that the isotopic signal in surface precipitation reflects a combination of atmospheric dynamics through moisture sources and atmospheric distillation, as well as cloud microphysics and below-cloud processes, we recommend caution regarding how Rayleigh distillation models are used during data interpretation. While the isotope compositions during convective precipitation events may be more adequately represented by idealized Rayleigh models, additional factors should be taken into account when interpreting a surface precipitation isotope signal from stratiform clouds.
Graph Deep Learning for Long Range Forecasting
Authors: Rühling Cachay Salva , Erickson Emma , Fender C. Bucker Arthur , Pokropek Ernest , Potosnak Willa , Sosei Salomey , Lütjens Björn
Published: March 2021

Deep learning-based models have been recently shown to be competitive with, or even outperform, state-of-the-art long range forecasting models, such as for projecting the El Niño-Southern Oscillation (ENSO). However, current deep learning models are based on convolutional neural networks which are difficult to interpret and can fail to model large-scale dependencies, such as teleconnections, that are particularly important for long range projections. Hence, we propose to explicitly model large-scale dependencies with Graph Neural Networks (GNN) to enhance explainability and improve the predictive skill of long lead time forecasts.

In preliminary experiments focusing on ENSO, our GNN model outperforms previous state-of-the-art machine learning based systems for forecasts up to 6 months ahead. The explicit modeling of information flow via edges makes our model more explainable, and it is indeed shown to learn a sensible graph structure from scratch that correlates with the ENSO anomaly pattern for a given number of lead months.

 
Numerical and experimental study of the vertical distribution of velocity and hydraulic gradient in the capillary fringe
Authors: Mahdavi Mazdeh Ali , Wohnlich Stefan
Published: March 2021

Capillary fringe plays an important role in the fate and transport of infiltrated solutes from agricultural lands. In this study, flow patterns and the vertical distribution of the velocity and hydraulic gradient inside the capillary fringe were investigated using FEFLOW calibrated by experimental data. An experimental box along with a real sample of capillary fringe from the study area (Sand and clay pit Brüggen, Germany) was used for the experiments. The dimension of the filled part of the box was 0.75 m long, 0.55 m high, and 0.150 m wide. To maintain a constant hydraulic gradient throughout the experiments the upstream and downstream groundwater levels were fixed to 7 cm and 3 cm, respectively. The horizontal velocity at different points inside the capillary fringe and the vadose zone was measured by injecting the fluorescent dye tracer (Uranin). At the end of the experiments, the soil samples are collected from different parts of the box for water content measurement. The results indicate that FEFLOW successfully estimates water content, overall flow pattern, and more importantly horizontal movement inside the capillary fringe. The streamlines are parallel to the groundwater table in the middle part.  Based on both experimental and numerical results, while there is a downward movement near the outflow, an upward movement was seen near the inflow. In previous studies, the velocity profile inside the capillary fringe was estimated using Darcy’s law, unsaturated hydraulic conductivity, and constant hydraulic gradient. The detailed comparison of measured water content and velocity with numerical modeling results showed that the constant hydraulic gradient assumption above the water table in previous studies is not valid. The vertical hydraulic gradient profile calculated by FEFLOW showed that the hydraulic gradient at the middle part of the box changes from 0.042 to 0.03. Moreover, the shape of the vertical hydraulic gradient profile is a function of the location in the box and soil type.

Keywords: Solute transport, Unsaturated zone, Streamline, Pore velocity, Hydraulic conductivity, FEFLOW
Palaeohydrologic interpretations of Holocene wet episodes recorded in stalagmites from Soreq Cave, Israel: Linking the magnetic and isotopic properties of speleothems
Authors: Burstyn Yuval , Shaar Ron , Keinan Jonathan , Ebert Yael , Ayalon Avner , Bar-Matthews Miryam , Feinberg Joshua M.
Published: March 2021

Soil-derived magnetic particles trapped in speleothems can retain valuable information on the physiochemical conditions of the overlying soil and changes in the hydrological system. However, a direct link between magnetic and isotopic properties of speleothems has been only qualitatively established and is known to vary regionally. Here we investigate two Holocene speleothems from Soreq Cave, Israel and provide evidence for strong coupling over centennial to millennial timescales between the inflow of magnetic particles (quantified using the magnetic flux index, IRMflux), δ13C, and rainfall amounts. The two stalagmites formed at separate intervals: one at ~9.5 ky BP capturing the transition from pluvial Eastern Mediterranean conditions associated with Sapropel 1 (S1) and a second at 5.4 ky BP recording mid-Holocene wet-dry cycles.

The late-Holocene speleothem shows an anomalously high δ13C episode that is correlated with extremely low IRMflux, indicating minimal contribution from overlying soils due to either (1) recently denuded soils, or (2) high overland and vadose runoff. By contrast, the mid-Holocene sample shows saw-tooth cycles in both δ18O and δ13C, which are interpreted as rapid climate fluctuations associated with rainfall changes. IRMflux during this period varies in-phase with the δ13C cycles; however, the peaks in IRMflux values precede those of the isotope values. The apparent lag in isotopic values may be explained by the faster response of the IRMflux to increased rainfall resulting from the rapid physical translocation of overlying soil particles via groundwater, compared with slower soil organic matter turnover rates, which may vary on timescales of up to thousands of years.

The separate palaeohydrological scenarios resolved from the two speleothems demonstrate how magnetic data can act as a powerful paleo-hydrology proxy, even in weakly-magnetized speleothems growing under semi-arid conditions.
A revised mineral dust emission scheme in GEOS-Chem: improvements in dust simulations over China
Authors: Tian Rong , Ma Xiaoyan , Zhao Jianqi
Published: March 2021

Mineral dust plays a significant role in climate change and air quality, but large uncertainties remain in terms of dust emission prediction. In this study, we improved the treatments of dust emission process in a Global 3-D Chemical Transport model (GEOS-Chem) v12.6.0, by incorporating the geographical variation of aerodynamic roughness length (Z0), smooth roughness length (Z0s), soil texture, introducing Owen effect and Lu and Shao (1999) formulation of sandblasting efficiency α. To investigate the impact of the modifications incorporated in the model, several sensitivity simulations were performed for a severe dust storm during March 27, 2015 to April 2, 2015 over northern China. Results show that simulated threshold friction velocity is very sensitive to the updated Z0 and Z0s field, with the relative difference ranging from 10% to 60% compared to the original model with uniform value. An inclusion of Owen effect leads to an increase in surface friction velocity, which mainly occurs in the arid and semi-arid regions of northwest China. The substitution of fixed value of α assumed in original scheme with one varying with friction velocity and soil texture based on observations reduces α by 50% on average, especially over regions with sand texture. Comparisons of sensitivity simulations and measurements show that the revised scheme with the implement of updates provides more realistic threshold friction velocities and PM10 mass concentrations. The performance of the improved model has been evaluated against surface PM10 observations as well as MODIS aerosol optical depth (AOD) values, showing that the spatial and temporal variation of mineral dust are better captured by the revised scheme. Due to the inclusion of the improvement, average PM10 concentrations at observational sites are more comparable to the observations, and the average mean bias (MB) and normalized mean bias (NMB) values are reduced from -196.29μg m-3 and -52.79% to -47.72μg m-3 and -22.46% respectively. Our study suggests that the erodibility factor, sandblasting efficiency and soil-related properties which are simply assumed in the empirical scheme may lack physical mechanism and spatial-temporal representative. Further study and measurements should be conducted to obtain more realistic and detailed map of these parameters in order to improve dust representation in the model. 
Empirical determination of the covariance of forecast errors: an empirical justification and reformulation of Hybrid covariance models
Authors: Carrio Carrio Diego Saul , Bishop Craig , Kotsuki Shunji
Published: March 2021

The replacement of climatological background error covariance models with Hybrid error covariance models that linearly combine a localized ensemble covariance matrix and a climatological error covariance matrix has led to significant forecast improvements at several forecasting centres. To deepen understanding of why the Hybrid’s superficially ad-hoc mix of ensemble based covariances and climatological covariances yielded such significant improvements, we derive the linear state estimation equations that minimize analysis error variance given an imperfect ensemble covariance. For high dimensional models, the computational cost of the very large sample sizes required to empirically estimate the terms in these equations is prohibitive. However, a reasonable and computationally feasible approximation to these equations can be obtained from empirical estimates of the true error covariance between two model variables given an imperfect ensemble covariance between the same two variables.   Here, using a Data Assimilation (DA) system featuring a simplified Global Circulation Model (SPEEDY), pseudo-observations of known error variance and an ensemble data assimilation scheme (LETKF),  we quantitatively demonstrate that the traditional Hybrid used by many operational centres is a much better approximation to the true covariance given the ensemble covariance than either the static climatological covariance or the localized ensemble covariance. These quantitative findings help explain why operational centres have found such large forecast improvements when switching from a static error covariance model to a Hybrid forecast error covariance model. Another fascinating finding of our empirical study is that the form of current Hybrid error covariance models is fundamentally incorrect in that the weight given to the static covariance matrix is independent of the separation distance of model variables. Our results show that this weight should be an increasing function of variable separation distance.  It is found that for ensemble covariances significantly different to zero, the true error covariance of spatially separated variables is an approximately linear function of the corresponding ensemble covariance, However, for small ensemble sizes and ensemble covariances near zero, the true covariance is an increasing function of the magnitude of the ensemble covariance and reaches a local minimum at the precise point where the ensemble covariance is equal to zero. It is hypothesized that this behaviour is a consequence of small ensemble size and, specifically, associated spurious fluctuations of the ensemble covariances and variances. Consistent with this hypothesis, this local minimum is almost eliminated by quadrupling the ensemble size.
Reconstruction of a realistic rainfall field for extreme events happened in mountain area
Authors: Abbate Andrea , Longoni Laura , Papini Monica
Published: March 2021

In the field of hydrogeological risk, rainfalls represent the most important triggering factor for superficial terrain failures such as shallow landslides, soil slips and debris flow. The availability of local rain gauges measurements is fundamental for defining the cause-effect relationship for predicting failure scenarios. Unfortunately, these hydrogeological phenomena are typical triggered over mountains regions where the density of the ground-based meteorological network is poor, and the local effects caused by mountains topography can change dramatically the spatial and temporal distribution of rainfall. Therefore, trying to reconstruct a representative rainfall field across mountain areas is a challenge but is a mandatory task for the interpretation of triggering causes. We present a reanalysis of an ensemble of extreme rainfall events happened across central Alps and Pre-Alps, in the northern part of Lombardy Region, Italy. We have investigated around some critical aspects such as their intensity and persistency also proposing a modelling of their meteorological evolution, using the Linear Upslope-Rainfall Model (LUM). We have considered this model because it is designed for describing the mechanism of orographic precipitation intensification that was identified as the main cause of that extreme events. To test and calibrate the LUM model we have considered local rain gauges data because they represent the effective rainfall poured on the ground. These punctual data are generally considered for landslide assessment, in particular for rainfall induced phenomena such as shallow landslides and debris flows. Considering our test cases, the results obtained have shown that the LUM has been able to reproduce accurately the rainfall field. In this regard, LUM model can help to address further information around those ungauged area where rainfall estimation could be critical for evaluating the hazard. We are conscious that our and other studies around this topic would be propaedeutic in the next future for the adoption of an integrated framework among the real-time meteorological modelling and the hydrogeological induced risk assessment and prevision.
Spatio-temporal effects of vegetated windbreaks on wind erosion and microclimate as basis for model development
Authors: Weninger Thomas , Scheper Simon , King Nathan , Gartner Karl , Kitzler Barbara , Lackoova Lenka , Strauss Peter , Michel Kerstin
Published: March 2021

Wind erosion of arable soil is considered a risk factor for Austrian fields, but direct measurements of soil loss are not available until now. Despite this uncertainty, vegetated windbreaks have been established to minimize adverse wind impacts on arable land. The study addresses these questions: i) How relevant is wind erosion as a factor of soil degradation? ii) How important is the protective effect of vegetated windbreaks? iii) Are systematic patterns of spatial and temporal variability of wind erosion rates detectable in response to weather conditions? 

Two experimental fields adjacent to windbreaks were equipped with sediment traps, soil moisture sensors, and meteorological measurement equipment for microclimatic patterns. Sediment traps were arranged in high spatial resolution from next to the windbreak to a distance of ten times the windbreak height. Beginning in January 2020, the amount of trapped sediment was analyzed every three weeks. The highest wind erosion rates on bare soil were observed in June and July. For unprotected fields with bare soil, upscaled annual erosion rates were as high as 0.8 tons per hectare, and sediment trapped increased in a linear fashion with distance from the windbreak. Soil water content near the surface (5 cm depth) was three percent higher at a distance of two times the height of the windbreak than at a distance of six times the height. For the same respective distances from the windbreak, we observed 29 days of soil water contents below the wilting point compared with 60 days.

The preliminary outcomes confirmed the expected effects of windbreaks on soil erosion and microclimate in agricultural fields. Prospective results from multiple vegetation periods will be used in an upscaling approach to gain informations for the whole basin. That is meant to be done by a combination with a soil wind erosion model which was so far used for regional modelling of wind erosion susceptibility.
Interhemispheric comparison of mesosphere/lower thermosphere winds from GAIA, WACCM-X and ICON-UA simulations and meteor radar observations at mid- and polar latitudes
Authors: Stober Gunter , Kuchar Ales , Pokhotelov Dimitry , Liu Huixin , Liu Hanli , Schmidt Hauke , Jacobi Christoph , Brown Peter , Janches Diego , Murphy Damian , Kozlovsky Alexander , Lester Mark , Belova Evgenia , Kero Johan
Published: March 2021

There is a growing scientific interest to investigate the forcing from the middle atmosphere dynamics on the thermosphere and ionosphere. This forcing is driven by atmospheric waves at various temporal and spatial scales. In this study, we cross-compare the nudged models Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) and Whole Atmosphere Community Climate Model Extended

Version (Specified dynamics) ( WACCM-X(SD)), a free-running version of Upper Atmosphere ICOsahedral Non-hydrostatic (ICON-UA) with six meteor radars located at conjugate polar and mid-latitudes. Mean winds, diurnal and semidiurnal tidal amplitudes and phases were obtained from the radar observations at the mesosphere and lower thermosphere (MLT) and compared to the GAIA, WACCM-X(SD), and ICON-UA data for similar locations applying a harmonized diagnostic.

Our results indicate that GAIA zonal and meridional winds show a good agreement to the meteor radars during the winter season on both hemispheres, whereas WACCM-X(SD) and ICON-UA seem to reproduce better the summer zonal wind reversal. However, the mean winds also exhibit some deviation in the seasonal characteristic concerning the meteor radar measurements, which are attributed to the gravity wave parameterizations implemented in the models. All three models tend to reflect the seasonality of diurnal tidal amplitudes, but show some dissimilarities in tidal phases. We also found systematic interhemispheric differences in the seasonal characteristic of semidiurnal amplitudes and phases. The free-running ICON-UA apparently shows most of these interhemispheric differences, whereas WACCM-X(SD) and GAIA trend to have better agreement of the semidiurnal tidal variability in the northern hemisphere.
Impact of Chelicorophium curvispinum on the concentration-discharge response of suspended sediment in the Rhine River
Authors: van der Perk Marcel
Published: March 2021

In an ongoing study to the decline in suspended sediment concentrations and loads in the Rhine river since the mid-1950s, the temporal changes in the power-law sediment rating curve parameters were examined. This revealed that the rating exponent of the rating curve increased substantially between the early and late 1980s. Until the early 1980s, the ratings curves were relatively flat with values of the rating exponent b varying around 0.2. In the mid-1980s, the exponent suddenly increased to a value between 0.4 and 0.6 and since then has remained within this range. This change in the rating exponent was mainly caused by a decrease in suspended sediment concentrations during low discharges. During high discharges, the suspended sediment concentration initially increased during the late 1980s, but this increase was nullified soon afterwards due to the declining trend in suspended sediment concentration.

The sudden increase of the rating exponent coincided with the period that the Ponto-Caspian Chelicorophium curvispinum (Caspian mud shrimp) invaded the Rhine river basin. This suggests that this suspension-feeder species bears the prime responsibility for this increase, although this hypothesis requires further independent evidence. The sudden increase in the rating exponent does however not manifest itself in the long-term gradual trend of declining suspended sediment concentrations and vice versa. Apparently, the sequestration of sediment by Chelicorophium curvispinum is only temporary: the suspended sediment sequestered during periods of relatively low discharges is likely remobilised again during periods of high discharge. This implies that the invasion of Chelicorophium curvispinum has not played a significant role in the decline of suspended sediment concentrations. The precise reasons for the gradual long-term decline in suspended sediment concentration remain yet unknown.
Regularity of rainfall timing across Ethiopia: implications for crop production
Authors: Wakjira Mosisa , Molnar Darcy , Peleg Nadav , Six Johan , Molnar Peter
Published: March 2021

Rainfall timing is a key parameter that farmers rely on to match the cropping season with the time window over which seasonal precipitation provides adequate soil moisture to meet plant growth demand. The unpredictability of rainfall timing affects the selection of an optimal growing season, and hence crop production in regions where rainfed agriculture (RFA) is practiced. In this study, we (a) map rainfall timing, and its interannual variability and changes over RFA areas across Ethiopia for the period 1981-2010, and (b) explore the impact of variability in rainfall timing on cereal crop production in the period 1995-2010.

For the mapping of rainfall timing, we used the quasi-global CHIRPS precipitation dataset over Ethiopia. We use information entropy on monthly rainfall to define the rainfall seasonality metrics, i.e. the relative entropy and dimensionless seasonality index, and map them in space. For rainfall timing attributes, we determine the onset, cessation, and length of the wet season from LOESS-smoothed cumulative pentad rainfall anomalies for each hydrological year. Changes in seasonality metrics and rainfall timing attributes are analyzed using non-parametric methods. We show that high seasonality (unimodal rainfall regime) is located in the northern part of the Ethiopian RFA area where high annual rainfall and high relative entropy are coincident, and where the onset of the rainfall season varies between mid-April to late-June and cessation occurs between mid-September to late-October. Low seasonality in the southern part of the Ethiopian RFA area shows low relative entropy regardless of the annual rainfall total. We observed a considerable interannual variability both in seasonality and rainfall timing over the study period, especially in the onset and length of the wet season. The length of the wet season and magnitude of seasonal rainfall are predominantly controlled by the timing of rainfall onset.

For the impacts of rainfall timing on crop production, we used cereal crop production data from the Central Statistical Agency of Ethiopia for the period 1995-2010 in 45 administrative zones. We carried out a parametric correlation analysis between rainfall timing and rescaled and de-trended crop production anomalies. We observe that anomalies in seasonal cereal crop production in RFA areas are significantly correlated with anomalies in rainfall onset (negatively) and the length of the wet season (positively), with a regional average production loss of 3% per pentad of late rainfall onset, and 2.7% per pentad of shorter length of the wet season. Seasonal rainfall is less strongly correlated with cereal crop production anomalies compared to the rainfall onset. These results show that the interannual variability in rainfall timing (start of the rainy season) even under present climate has strong impacts on crop yields in RFA areas in Ethiopia, and this may be exacerbated in a future climate.
ADHI: The African Database of Hydrometric Indices (1950-2018)
Authors: Rouché Nathalie , Tramblay Yves , Paturel Jean-Emmanuel , Mahé Gil , Boyer Jean-François , Amoussou Ernest , Bodian Ansoumana , Dacosta Honoré , Dakhlaoui Hamouda , Dezetter Alain , Hughes Denis , Hanich Lahoucine , Peugeot Christophe , Tshimanga Raphael , Lachassagne Patrick
Published: March 2021

The African continent is probably the one with the lowest density of hydrometric stations currently measuring river discharge, despite the fact that the number of stations was quite important until the 70s. In addition, there is a major issue of data availability, since the different existing datasets are scattered across vast regions, heterogeneous and often with a large amount of missing data in the time series. The aim of this African Dataset of Hydrometric Indices (ADHI) is to provide a set of hydrometric indices computed from an unprecedented large set of daily discharge data in Africa. The ADHI database is based on a new streamflow dataset of 1466 gauging stations with an average record length of 33 years and for over 100 stations complete records are available over 50 years. ADHI is compiling data from different sources carefully checked, based on the historical databases of ORSTOM / IRD and the GRDC, including also other contributions from different countries and basin agencies. The criterion for a station to be included in ADHI is to have a minimum of 10 full years of daily discharge data between 1950 and 2018 with less than 5% missing data. Some time series originating from different sources were concatenated, after making sure the rating curves applied on the different time periods to compute river discharge were similar. Data records were scrutinized to identify suspicious discharge records and time periods where gap-filling methods have been applied to the original records. The selected stations are spread across the whole African continent, with the highest density in Western and Southern Africa and the lowest density in Eastern Africa. They are representative of most of the climate zones of Africa according the Köppen-Geiger climate classification. From this dataset, a large range of hydrological indices and flow signatures have been computed and made available to the scientific community (https://doi.org/10.23708/LXGXQ9). They are representing mean flow characteristics and extremes (low flows and floods) but also catchment characteristics, allowing to study the long-term evolution of hydrology in Africa and support the modelling efforts that aim at reducing the vulnerability of African countries to hydro-climatic variability.
The role of citizen science as a tool of public information in water quality management in the Brantas catchment, Indonesia
Authors: Pramana Reza , Houser Schuyler , Rini Daru , Ertsen Maurits
Published: March 2021

Water quality in the rivers and tributaries of the Brantas catchment (about 12.000 km2) is deteriorating due to various reasons, including rapid economic development, insufficient domestic water treatment and waste management, and industrial pollution. Various parameters measured by agencies involved in water resource development and management and environmental management consistently demonstrate exceedance of the local water quality standards. Between the different agencies, water quality data are available – intermittently from 2009 until 2019 at 104 locations, but generally on a monthly basis. Still, opportunities to improve data availability are apparent, both to increase the amount and representability of the data sets. The opportunity to expand available data via citizen science is simultaneously an opportunity to provide education on water stewardship and empower citizens to participate in water quality management. We plan to involve people from eight communities living close to the river and researchers from two local universities in a citizen-science campaign. The community members would sample weekly at 10 locations, from upstream to downstream of the catchment. We will use probes and test strips to measure the temperature, electrical conductivity, pH, nitrate, phosphate, ammonia, iron, and dissolved oxygen. The results will potentially be combined with the data from government agencies to construct an integrated water quality data set to improve decision making and the quality of community engagement in water resource management.
Impact of the barotropic tides on the seasonal Indonesian Throughflow 
Authors: Richet Oceane , Sloyan Bernadette , Pena-Molino Bea , Nikurashin Maxim
Published: March 2021

The Indonesian seas play a fundamental role in the coupled climate system, featuring the only tropical exchange between ocean basins in the global thermohaline circulation. The Indonesian Throughflow (ITF) carries Pacific Ocean warm pool waters through the Indonesian Seas, where they are cooled and freshened. The incoming Pacific waters are strongly modified via vertical mixing driven by numerous ocean processes and ocean-atmosphere fluxes. The result is a unique water mass that can be tracked across the Indian Ocean basin and beyond. With our high-resolution regional model of the Indonesian Seas, designed with the MITgcm, we focus our study on the impact of the barotropic tides on the ITF. In fact, the strong tides coming from the Pacific and Indian Oceans enter in the Indonesian Seas through narrow straits and interact with the complex topography of the region (sills, islands, deep seas). This interaction between the tides and the topography impacts directly the ITF by modifying the transport toward the Indian Ocean.
Major ion composition and 87Sr/86Sr of groundwater in the coastal Gujarat alluvial plain, India
Authors: Qasim Abul , Singh Satinder Pal
Published: March 2021

Major ions, Sr concentration, and 87Sr/86Sr have been analyzed in groundwater of the coastal Gujarat Alluvial Plain, collected during monsoon, post-monsoon, and pre-monsoon seasons of 2016–2017. The major objective of this study was to understand the regional groundwater salinization mechanism. In the study area, the groundwater is mostly characterized by Na-Cl facies, with few samples of Ca-Cl, Ca-Mg-Cl, Na-Ca-HCO3, and Ca-Mg-HCO3 types. Whereas, the Narmada and the Tapi river water samples are particularly of Ca-Mg-HCO3 type. The hydrogeochemical facies evolution (HFE) diagram depicts the coastal groundwater freshening irrespective of the season ruling out the lateral seawater intrusion far inland. However, the 87Sr/86Sr and Br/Cl ratios strongly suggest the modern marine influence on the regional groundwater. In the plot of 1/Sr versus 87Sr/86Sr, most of the groundwater samples fall on the binary mixing line between the seepage groundwater and modern seawater endmembers. Therefore, we suspect that the up-coning of recently trapped seawater by groundwater over-extraction is the most plausible reason for the groundwater salinization, which indicate the vulnerability of the coastal Gujarat alluvial plain to the near future sea ingress under the global warming scenario. A few exceptional groundwater samples far north of the Narmada River show more radiogenic 87Sr/86Sr indicative of silicate weathering.
Atmospheric nitrated phenols at a mountain site in North China: compositions, phase partitioning, and aqueous formation
Authors: Wang Xinfeng , Li Min , Zhao Yanan , Du Ping , Liu Zhiyi , Li Hongyong , Shen Hengqing , Xue Likun , Wang Yan , Chen Jianmin , Wang Wenxing
Published: March 2021

Nitrated phenols in the atmosphere are receiving increasing attentions due to their light absorption and biological toxicity. However, the partitioning characteristics of nitrated phenols among gas, particle, and aqueous phases and the dominant influencing factors remain unclear. In this work, particulate, gaseous, and cloud water samples were simultaneously collected at the summit of Mt. Tai in North China in spring, summer and winter. The contents of 11 nitrated phenols in these samples were determined with an ultra-high-performance liquid chromatograph in tandem with a mass spectrometer. The total concentrations of nitrated phenols in PM2.5 were in the range of several to dozens of ng m-3, a little lower than those measured in gas phase. The total concentrations of nitrated phenols in cloud water were in the level of hundreds of µg L-1. Among the 11 nitrated phenols, 4-nitrophenol and nitrosalicylic acids were the most dominant compounds in PM2.5, while 4-nitrophenol and 2,4-dinitrophenol were the most abundant in gas-phase and cloud water samples. During cloud events, most nitrated phenols were mainly distributed in particle phase, except dinitrophenols which were mainly distributed in gas phase. The observed concentration ratios of aqueous nitrated phenols to those in gas phase were one to two orders higher than the theoretical Henry’s law coefficients in pure water. Moreover, the measured concentrations of particulate nitrated phenols were substantially greater than the theoretically predicted values. The above results indicate that nitrated phenols potentially formed via aqueous-phase reactions inside the cloud droplets or on the surface of particles. The much higher ratios of the sum of 4-nitrophenol and 5-nitrosalicylic acid to 2,4-dinitrophenol in cloud water than those in PM2.5 further confirms the enhanced formation via aqueous processes. Overall, aqueous-phase reactions were important sources of atmospheric nitrated phenols during cloud events and had significant influences on the abundance and distributions of nitrated phenols in different phases.
Preferential flows and the legacy of Peter F. Germann (1944-2020)
Authors: Abou Najm Majdi R. , Beven Keith
Published: March 2021

Peter Germann died on December 6th 2020 in Bern, Switzerland. Known for a wide range of contributions to the physics of soil-water interactions and flow, his name (along with Keith Beven, his career-long collaborator and fiend) is recognized by an entire generation of soil physicists and hydrologists who studies macropore and preferential flows. They both co-authored the classic, and highly cited 1982 review paper in Water Resources Research on Macropores and Water Flow in Soils. Peter’s PhD work between 1976-1980 was a study of soil-water relations based on maintaining a network of 35 nests of tensiometers at 10 different depths down to 3m. At that time, these were still manual tensiometers coupled to mercury manometers that were read every 2 to 3 days for 3 years. One of the features that this remarkable data set revealed was that during infiltration, wetting in some cases occurred at depths, apparently by-passing the tensiometers above. This is what we all now know as preferential flow. Another was the large heterogeneity in responses between sites and between wetting events. For the major part of his research career, Peter was a strong advocate for a reconsideration of the physics of water flow through soils and, in particular, for the limitations of the Darcy-Buckingham-Richards flow theory. Peter later developed the kinematic wave approach into a theory of viscosity (rather than capillarity) dominated film flows subject to Stokes’ law during infiltration. He summarised his research work in his 2013 book on the subject published by the University of Bern. Peter held academic positions at the University of Virginia in Charlottesville, at Rutgers University, and at the University of Bern back in Switzerland where he stayed until he retired in 2009, and held an Emeritus position until 2015.   He continued to publish papers until shortly before his death which followed 2 major strokes. In this talk, we will go over Peter’s main contribution and research highlights in the area of macropores and preferential flows. Peter was no stranger to EGU, and many know him and have met him in this session or others. For those who knew Peter, they will miss his enthusiasm, his critical mind, his genuine care for the state of soil physics, his thoughtful responses, and his humour. He was a great source of inspiration to us and many others. Peter will be missed by many in soil science.