bluuebunny/crossref_metadata_2025 huggingface dataset:
Radar rainfall nowcasting for flash flood forecasting
Authors: Imhoff Ruben , Brauer Claudia , van Heeringen Klaas-Jan , Uijlenhoet Remko , Weerts Albrecht
Published: September 2022

Radar rainfall nowcasting promises to result in more accurate and timely rainfall forecasts up to several hours in advance, compared to numerical weather prediction model forecasts. As flood early warning systems can benefit from this, we assessed the potential of radar rainfall nowcasting for (flash) flood forecasting with a large sample of 659 individual rainfall events for 12 catchments in the Netherlands. In this assessment, we tested four open-source nowcasting algorithms: Rainymotion Sparse (RM-S), Rainymotion DenseRotation (RM-DR), Pysteps deterministic (PS-D) and Pysteps probabilistic (PS-P) with 20 ensemble members. Eulerian Persistence (EP) forecasts and zero precipitation input (ZP) were the benchmark. The discharge forecasts had a 12-h forecast horizon and were issued for every 5-min step in the available nowcasts for the set of events. We regarded the simulations using the observed radar rainfall as reference.

We found that rainfall and discharge forecast errors increase with both increasing rainfall intensity and spatial variability. For the discharge forecasts, this relationship also depends on the initial conditions, as the forecast error increases more quickly with rainfall intensity, when the initial conditions are wet and groundwater tables are shallow. Overall, discharge forecasts using RM-DR, PS-D and PS-P outperform the other nowcasting methods.

Furthermore, we tested the potential for forecasting threshold exceedances by setting the highest discharge, per event, as threshold. Compared to benchmark ZP, a threshold exceedance is, on average, forecast 223 (EP), 196 (RM-S), 213 (RM-DR), 119 (PS-D) and 143 min (PS-P) earlier. The relatively high time profits with EP are counterbalanced by both a high false alarm ratio (FAR) and inconsistent forecasts. Contrarily, PS-D and PS-P show both lower FAR and inconsistency index values, which can lead to more trust in the simulations.

Based on this large-sample analysis, we conclude that all nowcasting methods have shown a benefit for short-term discharge forecasting compared to issuing no rainfall forecasts at all, though all have shortcomings. As forecast rainfall volumes are a crucial factor in (flash) flood forecasting, we recommend a future focus on improving this aspect in nowcasting.
Testing state-of-the-art radar-based precipitation estimates to simulate the exceptional European floods of July 2021
Authors: Saadi Mohamed , Furusho Carina , Belleflamme Alexandre , Chen Ju-Yu , Trömel Silke , Kollet Stefan
Published: September 2022

The July 2021 floods costed up to 200 lives and 30 billion euros of damages in Germany alone. The aftermath of this exceptional event was a wake-up call for questioning the ability of the hydrometeorological tools in providing timely and reliable flood forecasts, knowing that this kind of events will become more frequent due to global warming. For these events, we simulated the hourly streamflows of seven catchments in the west of Germany, by combining nine, partly polarimetric, radar-based rainfall products with two hydrological models: GR4H (Ficchì et al., 2019, 10.1016/j.jhydrol.2019.05.084), a bucket-style, lumped model, and ParFlow-CLM (Kollet and Maxwell, 2006, 10.1016/j.advwatres.2005.08.006), a distributed model that couples 3D sub-surface and overland flows. GR4H parameters were calibrated using more than 10 years of rainfall-runoff data, with emphasis on reproducing high flows, whereas ParFlow-CLM parameters were estimated based on landscape and soil properties. The key findings are as follows: (1) In comparison with estimates from rain gauges, all radar-based precipitation products underestimate the total precipitation depths for the 14th of July, with significant differences among the products. This is most likely due to strong coalescence processes below the height monitored by the radars. (2) The hydrographs simulated by GR4H and ParFlow-CLM are similar for 3 of the 7 catchments, whereas the differences in the remaining ones could be explained by the effect of human water management, not represented in ParFlow-CLM. (3) The ability to detect the exceedance of the 100-year flood highly depends on the precipitation product used, highlighting the need for reliable precipitation estimates to reproduce such exceptional events.
Water resources in Lebanon: an overview
Authors: Merheb Mohammad , Abdallah Chadi , Moussa Roger , Halwani Jalal
Published: September 2022

This work assesses the current situation of water resources in Lebanon in term of quantity and quality. Hence, 160 water resources studies were gathered from the literature and divided to three categories: water balance (44%), quality (42%) and management (14%). Each category was further divided into sub-topics. The analysis consists of qualitative analysis that discuss the studies topics and their temporal and geographical extent. And a quantitative analysis that compare results of different articles in each topic. Results show that the majority of studies are recent with 60% of the studies published after 2010. Moreover, disparities exist in the studies spatial distribution with only 25% covering the whole country while another 25% concentrated in the inland agricultural Beqaa plain. Moreover, the emphasis is greater on groundwater than surface water for quantity and quality. In term of precipitation, all studies agree on the high spatial variability but still there are difficulties estimating rainfall especially in mountainous and remote areas. Similarly, snow contribution is still poorly estimated and only available for small areas in Mount Lebanon were ground measurement stations exist. In addition, climatic trends show a tendency towards drier conditions, a shrinking snow cover, and an increase of extreme rainfall events frequency. Moreover, although surface hydrology studies are rare, the available ones show some regional pattern which is promising for prediction in ungauged locations. However, global change impact is poorly represented and the studies that exist point towards a decrease in river and spring discharges. On the other hand, groundwater studies show the prevalence of karstic aquifers with some characterized by a high storage capacity making them a pivotal source of water but also a vulnerable one due to their high infiltration rate. For water quality, the dominant hydro-chemical facies is Ca-Mg-HCO3 due to the prevalence of carbonate rocks. Moreover, the studies show a degradation in surface and groundwater quality. Salt water intrusion, nitrate and pesticides pollution are main challenges in coastal aquifer and agricultural areas respectively. Finally, the steady increase in water resources studies in Lebanon is, unfortunately, accompanied by a decrease in water quantity and a quality degradation.

 
Future changes in flash flood frequency and magnitude over the European Alps
Authors: Zander Marjanne , Viguurs Pety , Sperna Weiland Frederiek , Weerts Albrecht
Published: September 2022

Flash Floods are damaging natural hazards which often occur in the European Alps. Precipitation patterns and intensity may change in a future climate affecting their occurrence and magnitude. For impact studies, flash floods can be difficult to simulate due the complex orography and limited extent & duration of the heavy rainfall events which trigger them. The new generation convection-permitting regional climate models (CP-RCMs) improve the representation of the intensity and frequency of heavy precipitation. Therefore, this study combines such simulations with high-resolution distributed hydrological modelling to assess changes in flash flood frequency over the Alpine domain. We use output from a state-of-the-art CP-RCM to drive a high-resolution distributed hydrological wflow_sbm model (0.0088333 degree, ~1km2) covering most of the Alpine mountain range on an hourly resolution. First, the hydrological model was validated by comparing ERA5 driven simulation with streamflow observations from 130 stations (across Rhone, Rhine, Po, Adige and Danube basins). Second, an hourly wflow_sbm simulation driven by the CP-RCM downscaled ERAInterim simulation was compared to databases of past flood events to evaluate if the model can accurately simulate flash floods and to determine a suitable threshold definition for flash flooding and to determine a suitable threshold definition for flash flooding. Finally, simulations of the future climate RCP 8.5 for the end-of-century (2096-2105) and current climate (1998-2007) are compared for which the CP-RCM is driven by a Global Climate Model. The simulations are compared to assess if there are changes in flash flood frequency and magnitude using a threshold approach. Results show a similar flash flood frequency for autumn in the future, but a decrease in summer. However, the Future Climate simulations indicate an increase in the maximal flash flood severity in both summer and autumn leading to more severe flash flood impacts.
The emergence of household-level water insecurity through socio-hydrological processes in the semi-arid region of Ceará, northeast Brazil
Authors: Seigerman Cydney K. , Martins Eduardo Sávio , Nelson Donald R.
Published: September 2022

In the semi-arid region of Ceará, northeast Brazil, differential experiences of household water insecurity emerge through intertwined sociopolitical, hydrological, and technological processes. Household water security is broadly defined as access water of sufficient quality and quantity to live a good life. This paper presents ongoing research that integrates hydrological and meteorological data with qualitative social science methods to examine the relationship among local hydrological characteristics, water management strategies, and the emergence of local experiences of water (in)security in rural communities in the Cearense semi-arid region.

The Cearense semi-arid region faces significant challenges related to socioeconomic inequality and reliable water access. It is characterized by highly politicized water management, irregular inter and intra-annual rainfall rates, crystalline soils, and high evapotranspiration rates. Poor, rural households rely primarily on rain-fed subsistence farming and livestock raising. Local access to land, water, and physical infrastructure depends on decisions and policies that span the microlevel (i.e., individual and household levels) and macrolevel (e.g., community, municipal, state, and federal levels).

To elucidate the emergence of local experiences of water (in)security in the region, semi-structured interviews were conducted with regional water professionals and members of rural communities with different water management operations (i.e., community-based, water company-based, or government-based). Participant observation (e.g., collecting drinking water from the household cistern) and observation of local and regional water management meetings were also carried out. These methods were complemented by analysis of climate patterns and community-level hydrological characteristics, including the impacts of the most recent extensive drought (from 2012 to the present in many areas). Households use a variety of strategies to obtain drinking water and water for other household activities (e.g., washing clothes, watering plants, or supplying animals with water), which depend on access to household technologies (e.g., cisterns and in-house piped water) and water management of water sources (e.g., reservoirs, deep-wells, or rivers). The research highlights the heterogeneity of experiences of water access and management by rural communities, which is influenced by socio-hydrological relations involving differential access to water technologies, water management and public policies, and hydrological conditions across temporal, geographic, and social scales.
Understanding uncertainties in future evapotranspiration projections to study the impact of climate change on hydrology over France.
Authors: Lemaitre-Basset Thibault , Oudin Ludovic , Thirel Guillaume , Collet Lila
Published: September 2022

Air temperature increase due to climate change can lead to an increase in evapotranspiration, depending on whether the atmospheric demand is water or energy limited. This results in the intensification of the transfer from the continental hydrological compartment to the atmosphere. Investigating the uncertainties in the representation of potential evapotranspiration (PE) can provide a better understanding of the sensitivity of hydrological projections to atmospheric demand. This work summarizes our findings on different aspects about PE evolution under climate change and the uncertainties associated. First, we explored the relative importance of the contribution of PE formulations to the total uncertainty in PE projections, compared to the other steps in the modeling chain. Second, we evaluated the importance of the negative feedback of atmospheric CO2 concentration on evapotranspiration for hydrological projections by modifying the stomatal resistance equation in the Penman-Monteith equation according to three formulations proposed in the literature to evaluate the sensitivity of hydrological projections to vegetation responses.

Regarding the importance of PE formulations on PE projections, it appears that the relative role of formulations is minor compared to other sources of uncertainty (namely climate models and greenhouse gases emission scenarios). Regarding the impact of CO2, results highlight a zone of uncertain change from decreasing to increasing average annual runoff, depending on the emission scenario and stomatal resistance equation. Thus, in the north of France, where PE fluxes are energy-limited, various levels of runoff response are showed with three tested formulations. The use of a PE formulation with stomatal resistance as a function of atmospheric CO2 could be used as forcing of a conceptual hydrological model, to include vegetation responses.
Gender differences within hydrological risk perception: Floods and droughts in Italy and Sweden
Authors: Mondino Elena , Raffetti Elena , Di Baldassarre Giuliano
Published: September 2022

Floods and droughts keep causing enormous damage worldwide. Thus, understanding how people perceive drought and flood risk, and how this may change over time, can help researchers, practitioners, and policymakers assist communities at risk. In particular, identifying potential gender differences in the perception of hydrological risk can support fair disaster risk reduction policies which take such differences into account. With the support of three rounds of national survey data on risk perception, knowledge, and preparedness in Italy and Sweden, this study shows that the perceptions of drought and flood risk are heavily intertwined. It also shows that changes in perception over time are different between women and men, with women showing a higher fluctuation over time compared to men, especially concerning floods. These results and their implications bring evidence in favour of integrating gender into hydrological risk management efforts and risk communication, as well as promoting policies that simultaneously address flood and drought risk.
Assessing sediments export from the Nile to the Suez Canal and the associated risk to global shipping
Authors: Hanert Emmanuel , Randresihaja Riana , Amrouni Oula , Hzami Abderraouf , S. Fouad Sara , Heggy Essam
Published: September 2022

The Suez Canal is a major bottleneck of global shipping. The stranding of the Ever Given, one of the world's largest container ships, in early 2021 showed how much global supply chains depend on the Suez Canal. The canal navigability directly depends on the incoming fluxes of sediments, either through the entrance on the Mediterranean Sea or from smaller tributaries along the canal. Here we model the hydrodynamics of the southeastern Mediterranean Sea, Suez canal and northern Gulf of Suez with the multi-scale ocean model SLIM (www.slim-ocean.be). The model can locally achieve a resolution of about 50 m and hence explicitly describes the flow through the narrow branches of the canal. The hydrodynamic model is then used to drive a sediment transport model that represents the dynamics of several types of sediments originating from the Nile delta, from shorelines along the Mediterranean Sea, and from inland channels connecting the Nile to the Suez Canal. Model results allow us to estimate the sediment deposition rate within the canal under present and future climate, and for different land and river management scenarios. The latter include the impact of existing and future dams along the Nile River and irrigation practices within the Nile Delta. Our result suggest that the Nile River management directly impacts the Suez canal navigability. This interconnection between the Nile River and the Suez Canal calls for an integrative management strategy. 
Rarest rainfall events have greatest relative increase under climate change
Authors: Gründemann Gaby , van de Giesen Nick , Brunner Lukas , van der Ent Ruud
Published: September 2022

Future rainfall extremes are expected to increase due to global warming based on both theoretical considerations and climate model outcomes. Common (yearly) extremes and rare (decennial or centennial) extremes may be affected differently. Here we show that the rarer the event, the more it is relatively expected to increase in a future climate. For the mitigation scenario SSP1-2.6 and the high emission scenario SSP5-8.5 daily land rainfall extremes will increase by 10.5 % and 28.2 %, respectively, for yearly events and by 13.5 % and 38.3, respectively, for 100-year events by the end of this century. These numbers are based on frequency and extreme value analyses applied to 25 different CMIP6 earth system models, weighted for independence and performance. The findings are consistent and statistically significant across all 25 earth system models, 102 different model runs, and four different possible climate futures. Our results show distinct regional differences, with some regions disproportionally affected relative to others. This has important implications for engineering design standards, which need to be raised more for systems designed for the rarest events.
Evaluating the impact of climate change on water system vulnerabilities using multiple hydrological models 
Authors: Hassanzadeh Elmira , Sharifinejad Ali
Published: September 2022

Warming climate is altering streamflow characteristics and posing pressure on water systems. Here, the impacts of climate change on a headwater system in Alberta, Canada, is evaluated, with the primary goal of understanding the role of hydrological system representation. For this purpose, a conceptual hydrological model, i.e., HBV-MTL, is coupled with two snowmelt estimation modules, i.e., Degree-Day and CemaNeige. The models are calibrated using point- and grid-based climatic data and considering lumped and semi-distributed representation of the basin and are linked to a water allocation model to simulate reservoir dynamics and downstream water deliveries. The bias-corrected outputs of 19 climate models during 2021-2099 are then used to estimate the future water system conditions. Results show that during the historical period, all models provide acceptable performance, with minor distinctions; however, their simulations highly divergence in the future period. The models unanimously project significant water deficit in meeting agricultural water demands and flood risk in the future. However, the quantified vulnerabilities depend on the considered hydrological models, among the utilized snow routine module highly influences estimated natural and regulated flow values. It is suggested to consider these projections and revise the Oldman reservoir water allocation plans to mitigate climate change's adverse impacts on this water system.
Agent-based model to analyse human-drought feedbacks in dryland regions
Authors: Streefkerk Ileen , de Bruijn Jens , Haer Toon , van Loon Anne , Aerts Jeroen
Published: September 2022

The Horn of Africa Drylands (HAD) region is vulnerable to climate-related risks, including droughts. Drought is a persistent and costly hazard; it negatively impacts the environment, people’s livelihoods, access to education, and food security. The rural livelihoods of countries in the HAD region are highly dependent on rain-fed agriculture and livestock herding (agro-pastoralism), which is extremely sensitive to weather and climate variability. Communities can take adaptation decisions that influence the impacts of drought. In turn, adaptation behaviour by agro-pastoralists influences the drought hazard. However, only a few drought models incorporate these feedbacks in drought analysis. This research presents a dynamic drought adaptation modelling framework that combines socio-hydrological and agent-based modelling approaches. By coupling the spatially explicit hydrological Dryland Water Partitioning model (DRYP) with a behavioural model capable of simulating (bounded rational) behavioural theories, the model enables simulating the feedbacks between the environment and agro-pastoralists and amongst agro-pastoralists (both through ‘communication structures’ and indirectly via their water and land use). Qualitative and quantitative data inform the model parameterisation on adaptive decision behaviour of agro-pastoralists, applied to the upper Ewaso N’giro river basin in Kenya. We demonstrate the possibility of capturing adaptive human-drought feedbacks, laying the foundation for in-depth analysis of human-drought feedbacks and future climate and policy scenarios.
The connections between rainfall regimes and crop production in semi-arid and sub-humid climates: an example from Ethiopia
Authors: Wakjira Mosisa Tujuba , Peleg Nadav , Anghileri Daniela , Molnar Darcy , Alamirew Tena , Six Johan , Molnar Peter
Published: September 2022

Temporal distribution of rainfall is a crucial climatic factor that controls seasonal biomass productivity and crop yield, particularly in tropical semi-arid and sub-humid climates where agriculture is primarily rainfed. This study explores the relationship between temporal rainfall attributes – seasonality, timing, and duration of the wet season -- and cereal crop productivity in the rainfed agriculture (RFA) areas of Ethiopia using the CHIRPS rainfall. In the first step, we determined the rainfall seasonality using an entropy-based dimensionless seasonality index (DSI), defined the dates of onset and cessation from the cumulative rainfall anomalies, computed the duration of the wet season, and assessed the anomalies and trends in these attributes and their associations to El Niño–Southern Oscillation (ENSO) over the period 1981-2010. In the second step, we analyzed the correlation between de-trended total cereal production (the sum of maize, teff, sorghum, wheat, barley, millet, oats, and rice productions) during the main growing season (April - September), and anomalies of the temporal rainfall attributes during 1995-2010. We also estimated the effects of variabilities in the rainfall timing attributes on cereal production using a univariate linear regression model. We show that rainfall in the northern RFA areas of Ethiopia is highly seasonal and unimodal whereas the southern and southeastern parts are characterized by low seasonality and a bimodal regime. Anomalies in the onset dates and DSI are meaningfully related with ENSO: 54% of late-onset events and 50% of negative DSI anomalies during 1981-2010 were observed in El Niño years. The response of crop production to changes in the temporal rainfall attributes depends on the rainfall regime. In regions with unimodal and highly seasonal rainfall regimes, we found that cereal production is mostly correlated with the onset (median ρ=-0.39) and duration (ρ=0.24) of the rainy season, whereas in regions with semi-arid bimodal rainfall regime, cereal production is more correlated with the rainfall seasonality (ρ=0.21). The median cereal production losses due to late-onset and shorter duration over the RFA areas are estimated to be ∼1.5% and 1.1% per 5-day period respectively, but much larger losses of up to 12% can be experienced in some regions.
On the importance of soil moisture dynamics for flood generation in Africa
Authors: Tramblay Yves , Villarini Gabriele , El Mehdi Saidi Mohamed , Gründemann Gaby , El Khalki El Mahdi , Massari Christian , Stein Lina , Hughes Denis
Published: September 2022

In the context of an ever-increasing vulnerability to floods in Africa, it is important to encourage innovative research on the understanding of these extreme events, notably to improve warning systems and increase the resilience of socio-economic systems to global changes. A recently developed database with discharge data covering most regions of the African continent makes possible a continental-scale assessment of the main flood drivers. Two complementary analyses were performed; the first based on directional statistics to compare the timing of floods with annual maximum rainfall and soil moisture and the second one relying on a process-based classification of flood drivers. The results indicate that the annual maximum floods are more strongly related to the timing of the annual peak of soil moisture than of annual maximum precipitation. Furthermore, temporal changes in flood magnitudes are better explained by the variability of annual maximum soil moisture than by the variability in the annual maximum precipitation. About the dominant flood drivers, excess rainfall over saturated soils and long rainfall events are the main flood generating mechanisms, accounting for more than 75% of floods across the African continent. The relative contribution of the different flood’s drivers across a range of different catchments being strongly related to aridity conditions. The main implication of these results is that precipitation extremes should not be analyzed alone to explain the occurrence and temporal evolution of floods.
Mapping sustainable irrigation development potential with renewable groundwater in Africa
Authors: Altchenko Yvan , Villholth Karen , Ducharne Agnes
Published: September 2022

In Africa, groundwater irrigation is considered a reliable and affordable means to increase food security. Areas equipped for groundwater irrigation in Africa have however, developed slowly since 1950 and remain very limited. This study is based on two approaches to locate and quantify this potential. The quantitative hydrological approach is based on the estimation of the current crop irrigation need and available renewable groundwater for irrigation after all other water needs, including environmental, have been satisfied. This approach shows that the potential is 44.6 x 106 ha or 20.5% of the cropland over the continent. The environmental approach redefines the quantitative potential by considering a set of biophysical and socio-economic factors conducive to sustainable development of groundwater irrigation. The potential is then 19.3 x 106 ha and it is reduced mainly from the equatorial regions where the need for irrigation is limited. In fact, without considering the countries of the Maghreb and South Africa where current irrigation by groundwater exceeds the estimated potential, groundwater irrigated areas could be multiplied by 75. The largest areas which are worthwhile to develop are mainly located along a west-east line from Angola to the north of Mozambique and a line south of the Sahel. The dry regions of the Sahel, East Africa and Southern Africa have limited development potential which is more suitable to small-scale agriculture and could greatly improve food security in Africa.
Transdisciplinary characterisation of a complex coastal aquifer, for a sustainable exploitation of its groundwater resources in a Mediterranean context. The DEM'EAUX ROUSSILLON project.
Authors: Caballero Yvan , Duvail Cédric , Chazot Sébastien , Bouchette Frédéric , Dobricean Octavian , Balouin Yann , Berne Serge , Bourrin François , Champollion Cédric , Dall'Alba Valentin , Dewandel Benoît , Garin Patrice , Issautier Benoît , Ladouche Bernard , Lanini Sandra , Lofi Johanna , Montginoul Marielle , Neverre Noémie , Pezard Philippe , Renard Philippe
Published: September 2022

More than 80 million m3 per year are pumped into the Roussillon plain coastal aquifer, covering 850 km² and located between the Pyrenean massif to the west and the Mediterranean Sea to the east, south of France. This is a multilayer aquifer of more than 350 m thick, made up of sandy layers embedded in low-permeability clayey material from the Pliocene and topped by alluvial formations from the Quaternary. Its groundwater resource is primarily used for the supply of drinking water, but also contributes to the irrigation of some 13,000 hectares.

For more than 40 years, this aquifer has been undergoing a general decline in its piezometric level due to pumping and water demand is expected to increase (growing irrigation areas and climatic demand). Moreover, given its flat topography, the Roussillon plain is likely to suffer sea water intrusions and marine submersion, due to the sea level rise, which could reach 1 m by 2100.

This context shaped the Dem'Eaux Roussillon project, which brought together nearly ten partners from the Occitanie region (research units, consultancies and local authorities). Its objective was to characterise the behaviour of the groundwater resource in this aquifer, in order to be able to project its future situation, in the context of climate change, rising sea levels (risk of saline intrusion) and changes in water use. A detailed characterisation of the geological reservoir highlighted the need to consider the offshore extension of this coastal aquifer. The analysis of the piezometric evolution at the scale of the Roussillon plain over the last 50 years allowed the spatialized characterization of the hydrodynamic parameters and the understanding of the vertical drainage processes that control the hydraulic equilibrium between the Quaternary and the Pliocene water tables. Two high-resolution hydro-geophysical observatories have been set up to quantify these processes and improve understanding of saline intrusions processes. Finally, a conceptual model presenting the main features of the main processes controlling the groundwater evolution and the sea water intrusion risk was obtained ready to launch a numerical modelling work.
Évaluation de la qualité des eaux de surface à l'aide de techniques statistiques multivariées et de méthodes hydrochimiques : étude de cas de l'oued El Hatab (Centre de la Tunisie).
Authors: Hayouni Wafa , Chkir Najiba , Pistre Severin , Zouari Kamel
Published: September 2022

Multivariate statistical techniques, and hydrochemical tracers of surface water of wadi Hatab watershed, central Tunisia, are used to assess the surface water quality for drinking and irrigation purposes. Then, in this context, it is fundamental to identify the sources of water pollution in this basin which represents a good example of anthropized and exploited basin in semi-arid region.

Stream chemistry was monitored in 28 sampling sitesThe projection of major ions on the Piper diagram reveals a variability of water chemical facies. It indicates that water mineralization is primarily governed by sodium, magnesium and calcium for cations and sulphates and chloride for anions. Surface water salinity ranged between 0.364 g/l to 29.173 g/l, and exceeds the WHO standard of salinity for 82% of stations. This variation is explained by domestic and industrial discharges in watershed and by the proximity of a salt-water source draining evaporitic formations. With naturally occurring mineralization, an anthropogenic mineralization is observed which is linked to domestic discharges, untreated industrial activities including paper mill discharges, and poorly controlled agricultural practices.

Several water quality parameters were applied for drinking and irrigation purposes. Water quality index (WQI) values indicate that 75% of surface water quality are not suitable for drinking usage. According to Percent Sodium (%Na), Residual Sodium Carbonate (RSC), the electrical conductivity (EC) and Wilcox classification, 85% of surface water samples are suitable for agricultural irrigation activities. Based on Sodium Adsorption Ratio (SAR) and USSL classification, it appears that only 47 % of water samples, mostly locared in the western part of the watershed, are suitable for irrigation use and almost 53 % of these samples are “good” or “permissible”.

This study demonstrated the impact of several processes on surface water resource. The dataset revealed that water physiochemical properties are mainly controlled by regional lithological features, but the nature of the discharges that are dumped there significantly changes it. In this respect, this research provides insights for sustainable water management. Generally, this study suggests the need and feasibility of multivariate statistics and hydrochemical techniques to evaluate chemical water quality and to determine the origin of water pollution.
Multivariate statistical assessment of flood scenarios in large river basins under consideration of tributary impacts and flood types
Authors: Fischer Svenja , Schumann Andreas
Published: September 2022

Despite the assumption of a homogeneous sample in many flood frequency analyses, flood events can be generated by highly different meteorological and catchment conditions. In large river basins, the diversity of flood generation is increased even more due to spatial and temporal variability of meteorological loads and hydrological processes within the basin and the resulting event-specific flood superposition of main river and tributary floods. Any consideration of additional attributes increases the complexity of statistical characterisation of flood events and scenarios. However, consideration of such differences is imperative if the effectiveness of flood control measures is to be assessed in a spatial context. This is mostly done by flood scenarios, which are usually derived using individual historical floods along with deterministic model-based simulations. We, instead, performed hydrograph-based flood-type classification and volume-based runoff analyses to estimate the contributions of sub-basins to floods in large basins. Using this information, we generated long synthetic samples of peak-volume-pairs to apply a multivariate statistical flood-frequency model that yields a type-specific conditional probability of a flood peak given the peaks in tributary stations. The results show that only some combinations of flood types may result in extreme peaks downstream of confluences. They also highlight the need to distinguish runoff-generation mechanisms for the larger floods from ones that drive smaller, more frequent events. Finally, design floods for different scenarios of flood-type combinations and assigned probabilities are derived, an approach that can be used to assess possible climate impacts to flood frequency. Case studies in several large river basins in Central Europe demonstrate the importance of distinguishing between flood types and flood scenarios, especially for extreme flood events.
Modeling Nitrate export with GR4J and StorAge Selection functions 
Authors: de Lavenne Alban , Tournebize Julien , Henine Hocine , Chelil Samy , Andréassian Vazken
Published: September 2022

Models based on StorAge Selection (SAS) functions are emerging as promising tools for quantifying catchment-scale solute export through the understanding of factors controlling transit time distribution (TTD). SAS functions describe the sampling of different ages in catchment storage that produces river discharge. This sampling varies over time, for example in such a way that the young water fraction is generally higher during high flows and lower during low flows. Literature thus proposed different parametrization of SAS functions in order to make them dynamics according, for instance, to soil moisture or antecedent inputs.  

In the first step of this work, we investigated how the time variance of the SAS functions could be related to the different fluxes and model states of the hydrological model GR4J. Chloride concentrations are used as a conservative tracer to evaluate different modelling hypotheses. In a second step, we investigated how TTD could be used to understand the dynamics of a non-conservative solute such as nitrate. In addition to the solute transport, we described the relationship between water age and denitrification at catchment scale. We assumed that nitrate removal is higher when young water fraction is lower, and we investigated the seasonal dynamics of this assumption. These hypotheses are tested by exploring the detailed water quality record from the Orgeval catchment (ORACLE observatory, France) where it is possible to assess various scales of nested catchments (up to 104 km²). 
Comparison of One-Site vs Multi-Sites calibration/validation schemes for hydrological modelling of nested watersheds in the West African Sahel
Authors: Gbohoui Yetchékpo Patrick , Yonaba Roland , Fowé Tazen , Paturel Jean-Emmanuel , Karambiri Harouna , Yacouba Hamma
Published: September 2022

Abstract:

Runoff simulation in highly anthropized watersheds is complex, but essential for water management, especially in poorly gauged and data-scarce hydrosystems of the West African Sahel. In this study, the physically-based and semi-distributed hydrological model SWAT (Soil and Water Assessment Tool) was applied to simulate daily runoff in the Nakanbé watershed at Wayen (21,178 km2) in Burkina Faso over the period 2006-2012. The data used concerned 9 water reservoirs, 5 hydrometric stations, 15 rain gauges, 3 synoptic stations, a digital elevation model (spatial resolution: 30m), a soil map (scale: 1:5,000,000), a land use and land cover map (scale: 1:200,000). The 5 hydrometric stations (Tougou, Dombré, Rambo, Ramsa and Wayen) gauge 5 nested watersheds ranging in size from 38 to 21,178 Km2. The added value of nested watersheds was assessed through the following three calibration/validation (C/V) schemes: one-site C/V (OS) at the watershed outlet (Wayen); multi-sites C/V considering nested sub-basins (MS1) and multi-sites C/V without considering nested sub-basins (MS2). The results at the watershed outlet (Wayen) indicated that the three C/V schemes (OS, MS1, MS2) are overall satisfactory (KGE above 0.7). However, MS2 scheme (KGE = 0.75) performed better as compared to the traditional one-site calibration scheme (OS: KGE = 0.73). On the other hand, the MS1 scheme (KGE =0.71) performed worse than the OS scheme. The water balance analysis at Wayen showed that 60 to 90% of the annual rainfall is lost as evapotranspiration whereas 5 to 8% contributes to surface runoff, groundwater recharge remaining very low. The comparison of the three calibration/validation schemes provides evidence that accounting for nested sub-basins does not necessarily improve the quality of rainfall-runoff simulations. Yet, multi-sites modeling remains the best scheme when the watersheds used are not nested. The availability of higher resolution data might allow a better understanding of spatial scale effects.

Keywords:

Nested watersheds, SWAT model, Nakanbé, West Africa Sahel, Burkina Faso.
Understanding changes in flood magnitude and timing
Authors: Wasko Conrad , Nathan Rory , Peel Murray , Stein Lina , O'Shea Declan
Published: September 2022

Small shifts in the climate can have large consequences on flood timing and magnitude. For example, changes of only 1-2 degrees Celsius and 10–20% in annual precipitation can cause order of magnitude changes in flooding. Changes in flood magnitude and timing can affect flood risk, farming productivity, the health of ecological systems, and impact water supply reliability.

Here we examine changes in both flood magnitude and timing across the world with a focus on Mediterranean and semi-arid climates, such as those in south-west Australia, which are dominated by dry summers and wet winters. Relative to other climates across the world, we find semi-arid regions are particularly susceptible to drying antecedent moisture conditions, with the largest decrease in antecedent soil moisture of any climate zone across the world. 

Drying antecedent soil moisture conditions in semi-arid regions are causing a shift to a later onset of flooding in the wet season. Despite increases in extreme rainfall magnitudes, frequent floods, such as those expected to occur on average once per year, are decreasing in magnitude due to the impact of drying antecedent moisture conditions more than offsetting the impact of increasing extreme rainfall. Only rarer events, such as those expected to occur once every 10 years, are increasing in response to increases in extreme rainfalls, where the increase in extreme rainfall outweighs the decrease in soil moisture. These results point to smaller floods, such as responsible for filling our water supplies, decreasing, while the larger flood events that pose a risk to life and infrastructure are increasing, with semi-arid regions particularly susceptible to these changes.
Analysis of long-term changes in inundation characteristics of near-natural temperate riparian habitats in the Lower Basin of the theBiebrza Valley, Poland
Authors: Kochanek Krzysztof , Grygoruk Mateusz , Mirosław-Świątek Dorota
Published: September 2022

Studying reference ecosystems and their specific features provides information to be used as background principles for ecosystem management. In the case of riparian wetlands, these are hydrological indicators (such as average water levels, flooding extents and flood duration) that are either used as criteria for ecosystem conservation or remain easy-to-measure targets for habitat restoration. We focused on revealing whether any trends in flood extents and durations of inundation exist within near-natural temperate floodplains persisting under the natural lowland river flow regime. We analysed whether the fraction of inundation time in a year (FIT) changed over time. River discharge data from 1951 to 2011 applied as boundary conditions in a 1D hydrodynamic model were used to generate flood extents and durations in the Lower Basin of the Biebrza Valley. We found no substantial trends in flood extents and flood durations in both time-dependent mean and standard deviation. We revealed that the average, long-term values of the FIT, influence the persistence of Caricetum approprinquatae, Caricetum gracilis, Glycerietum maximae and Phragmitetum communis, reached, respectively, 0.33, 0.43, 0.49 and 0.53 and did not present trends. Variability of the FIT within particular plant communities was high. The main challenges in conservation of temperate riparian wetlands are likely related to appropriate management addressing nonlinear climatic pressures.
Flows variability in a forest watershed undergoing accelerated urbanization: the case of Mefou (South Cameroon)
Authors: Ebodé Valentin Brice , Mahé Gil , Braun Jean-jacques , Dzana Jean-guy , Ndam Ngoupayou Jules Remy , Nka Nnomo Bernadette
Published: September 2022

The objective of this study is to understand the impact of rainfall variability and anthropization on the flows of the Mefou watershed over a recent period. For this, the hydropluviometric data of the catchment concerned were analyzed using the Pettitt test. Likewise, the dynamics of the main land-use patterns have been assessed, using supervised classifications carried out from the processing of Landsat satellite images of the basin studied at two dates. The results of this study show that the average and extreme flows of this basin have been increased since 1985-86, unlike the rainfall, which generally decreases for all seasons from the 1970s, apart from the summer, where the reverse is observed. Land-use changes (increase in impervious areas and a decrease in forest and water bodies) seem to be the main cause of the observed increase in runoff. The rainfall changes observed in this basin have just contributed to amplifying this increase in runoff in some cases and attenuating it in others. The summer and the spring for which the rainfall recorded respectively an increasing break and no break are also the seasons for which the increases in runoff are the most important. Conversely, autumn and winter, which saw significant decreases in rainfall, experienced the smallest increases. These results could be useful for long-term planning of water demand and use in this basin, as well as for improving future simulations of main collector flow and preventing socio-environmental disasters like flooding.

Keywords: Mefou, variability, precipitation, runoff, land use patterns
Modeling erosion and reservoir impacts in data sparse regions in South Africa
Authors: Brendel Conrad , Bartosova Alena
Published: September 2022

Reservoir sedimentation is a major problem in South Africa that impacts drinking water supplies, irrigation, recreation, hydropower production, and flood control. Although South Africa has been actively involved in research and monitoring of erosion and sedimentation, an ongoing challenge with assessing reservoir sedimentation is that many basins are ungauged and information required to guide policy and decision making is not available. Thus, there is a need to better understand methods to estimate sediment yields in these areas. Hydrological models can provide detailed spatial and temporal estimates of sediment fluxes. However, when modeling data sparse regions, it can be challenging to find a balance between model complexity and data availability to not only optimize simulation performance, but also to not overparameterize the model.

In this study, we used the open source, semi-distributed Hydrological Predictions for the Environment (HYPE) model to investigate how model routines with different data requirements affected simulations of long-term reservoir sediment yields within the uMngeni River basin in South Africa. Specifically, we assessed the impacts on model performance due to selection of the erosion routine and the stream sedimentation/resuspension method. An ensemble of models for the uMngeni basin was calibrated to sediment yields calculated from reservoir surveys and suspended sediment sampling data for seven reservoirs. In total, the ensemble consisted of 12 model setups representing unique combinations of two erosion routines (Morgan-Morgan-Finney model and HBV-SED index method), three HBV-SED seasonal erosion correction methods (no adjustment, values from earth observation indices, and calibrated values), and three stream sedimentation/resuspension routines (based on bankfull flow, based on bankfull flow with calibrated correction factor, and the Bagnold equation). Upon completion of the ensemble calibration, a matrix of model fit statistics was created to evaluate how sediment simulation performance varied according to model routine complexity and input data requirements. Erosion rates, sources of sediment fluxes, and sediment yields were also compared between the model setups to provide guidance on ranges of potential reservoir impacts. Results from this study can inform the selection of modeling techniques during the development of sediment flux models for regions with limited data.
PEMANFAATAN Aspergillus japonicus PADA BEBERAPA JENIS MEDIA PERBANYAKAN TERHADAP PERTUMBUHAN BIBIT TANAMAN KAKAO (Theobroma cacao L.)
Authors: Hasmira Hasmira , Wisdawati Eka , Darwisah Baso
Published: September 2022

ABSTRAK

 

Tujuan dari penelitian ini ialah  untuk mengetahui pengaruh beberapa jenis media perbanyakan cendawan Aspergillus japonicus dalam meningkatkan pertumbuhan tanaman kakao. Metode Percobaan ini menggunakan Rancangan Acak Kelompok (RAK) dengan 4 perlakuan. Perlakuan tersebut adalah P0 (Tanah), P1 (Aspergillus Japonicus + Beras), P2 (Aspergillus Japonicus + Jagung), P3 (Aspergillus Japonicus +  Sekam). Penelitian ini dilaksanakan di Screen House Jurusan Budidaya Tanaman Perkebunan Kampus Politeknik Pertanian Negeri Pangkep. Hasil pengamatan menunjukkan bahwa Pada 6 & 7 HSI, pertumbuhan A. japonicus pada media perbanyakan tidak memperlihatkan perbedaan yang nyata kecuali pada media sekam selain itu media perbanyakan jenis cendawan Aspergillus japonicus + sekam merupakan media yang memiliki respon pertumbuhan yang lebih cepat  terhadap pertambahan diameter batang bibit tanaman kakao.

 

Kata Kunci     : Media Perbanyakan, Cendawan, Aspergillus japonicus.