bluuebunny/crossref_metadata_2025 huggingface dataset:
On the use of water stable isotopes to estimate snow and ice melt contribution in a glaciated catchment
Authors: Müller Tom , Schaefli Bettina , Lane Stuart N. , Fischer Mauro
Published: September 2022

Glaciated catchments in the Swiss Alps are subject to intense changes due to rapid glacier retreat. Combined with earlier snowmelt, water availability in summer and especially during drought periods will become limited, which will have a strong influence on the local ecology but also for downstream water usages.

Water stable isotopes have become a commonly used tracer in hydrological studies to separate the contribution of snow and rain, due to their distinct signature and conservative behaviour, but also due to their simple sampling procedure and low analysis costs. In high alpine catchments, their application is however challenging because the temporal and spatial isotopic composition of ice and snow varies strongly (which requires intense sampling) and because their isotopic signal range is often strongly overlapping

Based on a case study of a glaciated catchment in the Swiss Alps, we propose in this study to compare the estimation of snow and ice melt contribution using two separate approaches: a glacier surface mass balance modelling approach, and a separation using a large database of isotopic observations. We show the large spatial and temporal variation of the snow isotopic signal at the catchment scale and propose a simple modelling approach to reconstruct its temporal evolution. On this basis, we show that snow and ice melt isotopes show very similar ranges of values during the summer due to the effect of rain on snow and snow fractionation. As a result, it appears that the estimation of their respective contribution is very sensitive to the accuracy of the estimated snow melt end-member. In comparison, the mass balance modelling approach may provide more robust results but requires a more field intensive work in order to measure snow accumulation and ice ablation. Finally, we insist that water stable isotopes should only be used with a proper statistical assessment of their spatial variability and a proper characterization of their temporal evolution in order to provide any realistic estimations in glaciated catchments.
Evap’Eau project: Estimating actual evapotranspiration from remote sensing in Senegal and Niger
Authors: Dezetter Alain , Demarty Jerôme , Etchanchu Jordi , Ogilvie Andrew , Bodian Ansoumana , Ndiaye Papa Malick , Diop Lamine , Issoufou Hassane Bil Assanou
Published: September 2022

This project, financed by ICIREWARD UNESCO center of Montpellier, is part of his WP2 "Large-scale hydrosystem processes to assess changes in the availability and quality of water resources caused by climate change" of the UNESCO centre's project. It also includes a skills transfer component for permanent or future researchers and training for doctoral students and students.

Evapotranspiration (ET) is a surface process that ensures the recycling of water and the redistribution of incident energy to the near atmosphere. In this way, it links the major continental water and energy cycles and is a major variable of interest for studies on the management and monitoring of hydro(geo)logical and plant resources (closure of water balances, monitoring of water tables, irrigation management, crop forecasting, etc.). This is all the more the case in West Africa, where ET accounts for more than 85% of rainfall (Velluet et al., 2014) and where the human pressures on the environment in terms of land use and occupation are real societal issues. These significant changes in the territory, coupled with the current and future effects of climate change, exacerbate the pressures on sensitive ecosystems where the balance of natural resources is already fragile. The proposal of methodologies to monitor and anticipate changes in green water resources (including ET) is therefore a major scientific challenge.

Satellite data acquired in the thermal infrared range provide access to a key energy balance variable, i.e. the surface temperature (ST). This variable is correlated, depending on the intensity of water stress, with ET. Over the last few decades, several algorithms have been proposed to exploit this link, and consequently to estimate ET from ST. In spite of this popularity, the current challenge is the ability of these algorithms to generate sufficiently robust, accurate and frequent products to establish annual-scale balances.

This project aims to assess the potential of the different types of satellite-based ET approaches currently applied in West Africa, not only by comprehensively reviewing and testing the ET products available in the region, but also by actively contributing to the generation of new and more reliable products.
Evaluating water Ecosystem Services Footprint of agricultural production under climate change scenarios
Authors: Pacetti Tommaso , El Jeitany Jerome , Caporali Enrica
Published: September 2022

Based on the integration of hydrological modelling and Water Footprint (WF) analysis, this study aims at developing a methodology to analyze both the supply and demand of Water related Ecosystem Services (WES) connected to the agricultural sector under climate changes scenarios. The WES demand by the agricultural sector is determined using the WF Assessment methodology estimating the green, blue, and gray WF component and their variability due to climate change. The WES supply is analyzed by applying the Soil Water Assessment Tool (SWAT). The model simulates the main hydrological processes thus allowing the spatial explicit quantification of the variables estimating the water availability in its three components. After calibration and validation, possible scenarios of changes in water availability are evaluated under 20 climate change scenarios by means of  12 indicators of Hydrologic alteration (IHA) being the most representative of the flow regimes in Europe. Finally green, blue, and gray WES Footprint (WESF) through dedicated indicators in order to identify the main hotspots in agriculture water management and their future projections. The methodology is applied to a specific case study in the upstream part of the Arno River basin (Central Italy). The analysis allows the spatial explicit identification of the main hotspots associated to agricultural production in future scenarios. All scenarios outlined hydrological parameters that alter flow regime and affect surrounding ecosystem, despite a discrepancy between the northern part and the southern part on the basin. Magnitude of variability in monthly water availability and the changes in WF are explored suggest possible challenges to address. The use of footprint indicators, and in particular of WESF, can lead to a more sustainable water management revealing hidden costs and impacts of production of goods and services and sustaining the formulation of a conscious and integrative basin management plan.
Assimilation of SWOT discharge versus water level into CTRIP-12D over the Congo Basin
Authors: Munier Simon , Boone Aaron , Biancamaria Sylvain , Le Moigne Patrick
Published: September 2022

Land Surface Models are key tools to study the continental water cycle and can be used to better understand the main hydrological processes and their sensitivity to climate change. Yet, they are subject to potentially large errors, especially over ungauged basins where they cannot be calibrated or validated. The Surface Water and Ocean Topography (SWOT) satellite mission will provide unprecedented measurements of water elevation for all rivers wider than 100 m worldwide. Many recent studies focused on the assimilation of such observations into global hydrologic models, including ISBA-CTRIP developed at Météo-France, and they have demonstrated its added value. The SWOT mission will also provide discharge estimations derived from observed water elevation, river width and slope. The algorithms require ancillary data, such as the roughness coefficient, which needs to be estimated empirically at the global scale, potentially resulting in large errors in the discharge estimation. Yet, it is still unclear whether assimilating discharge instead of water level (or water level anomalies) would lead to better performances in terms of simulated discharge along the river network. In this study, we extended the assimilation of water elevation to river discharge into the CTRIP river routing model. We used the new version of the model at a 1/12 degree spatial resolution, which is more compatible to the resolution of the SWOT discharge product (reach length of about 10 km). The Congo river basin is chosen as a test case. SWOT-like river elevations and discharges are constructed by adding realistic errors to elevations and discharge provided by an independent river routing model, MGB. Also, a realistic satellite orbit is used to provide times and locations of available SWOT observations. The impact of observation errors on the assimilation is analysed, as well as the propagation of discharge corrections through the river network. Finally, model performances using discharge assimilation are compared to those using water level assimilation.
Unknown knowns: a missing piece of the uncertainty quadrant in hydrology
Authors: Khatami Sina , Di Baldassarre Giuliano , Moallemi Enayat A , Erndtson Henrik
Published: September 2022

Uncertainties — of different types, sources, and their characterisation methods — have been studied for years in environmental sciences and beyond, until Donald Rumsfeld gave it a new kick and audience. The terms known knowns, known unknowns, and unknown unknowns have become more prevalent to map out different types of uncertainties associated with understanding, modelling, and managing complex systems; even though these terms had been used in scientific literature before Rumsfeld’s remarks. The last piece of this quadrant that is less discussed is unknown knowns, i.e. the knowns that are treated as unknowns, that we have overlooked, forgotten, or ignored. In this work, we would like to emphasis on unknown knowns by discussing a few examples of them in scientific inquiries in general, and hydrological sciences in particular; from socio-economic factors to unconscious biases in formulating and analysing complex human-water systems. For example, in many cases the modellers’ choice of hydrological models is biased toward legacy (of existing models within the repertoire of the modellers) than based on adequacy. While human-water interactions are inherent in catchment processes, most common catchment models do not have a module to account for human activities and policy feedback. Neglecting such basic knowns — unknown knowns — can bias our analyses, decision making, and the narratives established to explain or react to a phenomenon such as drought. For instance, the “Zero Day” narrative of the Cape Town water crisis (around 2017). While the hydro-climatic multi-year drought was a contributing factor to the water shortage, the regional politics and water management also played a major role. Despite dramatic drop in water supply and hence drastic restrictions in water consumption across multiple sectors, water consumption by industrial users with political connections (such as local licensed Coca-Cola manufacturers) remained disproportionally higher. In effect, the zero day was only zero for some and not for everybody. To advance hydrological sciences, particularly to integrate socioeconomic and policy feedback interactions into the mainstream hydrological modelling, hydrologists can learn from such advances in neighbouring disciplines (e.g. sustainability science and system dynamics) and account for less conventional types/sources of uncertainties, especially unknown knowns.
Advancing the Science and Practice of Hydrology: Past and future contributions of UNESCO-IHP
Authors: Jewitt Graham , Mishra Anil
Published: September 2022

Since 1975, the Intergovernmental Hydrological Programme (IHP) has enabled and supported an interdisciplinary and integrated approach to watershed and aquifer management. Through the years, IHP officers and projects have combined a rigorous understanding of hydrologic processes with the recognition of the value of sound water resources management policies. As such, it has strived to incorporate social dimensions of water and to support international cooperation in hydrological and freshwater sciences. As an international science and policy programme, it occupies a unique interface with policy-makers, and has a strong history of supporting the development of both institutional and individual capacity to understand and manage water resources.

Through these initiatives, IHP has played an important role in advancing the science and practice of hydrology and as a uniquely international programme, has played a particular important role in broadening hydrology as science and bringing in perspectives and ideas reflecting knowledge across the spectrum of its member states. As we move towards the 50th anniversary of IHP, it is an opportune time to reflect on the state of hydrology as a science and its practice in supporting water resources management and the role that IHP has played. This presentation provides a reflection on the role of IHP in the development and practice of the science of hydrology and considers the role that the next phase of IHP i.e. IHP - IX i.e. “Science for a Water Secure World in a Changing Environment” can play in the development and application of hydrological as a science in the future.
ROBIN - A Reference Observatory of Basins for INternational hydrological climate change detection
Authors: Hannaford Jamie , Barker Lucy , Turner Stephen , Dixon Harry , Griffin Adam , Killeen Alannah
Published: September 2022

Future climate projections suggest hydrological extremes (floods and droughts) will become more frequent and severe, further heightening the already substantial impacts they cause to lives and livelihoods, infrastructure and economies. To adapt to future changes in water availability, we need projections of future flood and drought occurrence. Numerical simulation models are used to provide such scenarios, but they are complex and highly uncertain. To better understand and constrain these model-based projections, we need to quantify emerging trends in the water cycle. This requires long records of past hydrological observations; river flows are especially useful because river flows integrate climate processes over the large areas covered by drainage basins.

There have been many studies of long term changes in river flow around the world, but past research, confidence in observed trends remains very low. This is primarily due to the modification of river flows by human activities (e.g. presence of dams, abstraction of water for irrigation or human consumption, etc.). These disturbances can obscure the ‘signal’ of climate change, i.e., trends in many rivers may bear no relation to global warming and may be opposing the climate trend. To detect climate-driven trends we need to analyse river basins that are relatively undisturbed by such human impacts. To this end, many countries have ‘Reference Hydrometric Networks’ (RHNs) of minimally altered catchments providing high quality data. However, these are sparse, globally, and there is a need for an integrated approach to advance international assessments of hydrological change, that are a foundation of international assessments such as the IPCC Reports.

Here we introduce the ROBIN initiative, where we are advancing a worldwide effort to bring together a global RHN. With a growing network of partners from 20 countries spanning a broad range of climates and geographies, ROBIN will develop a network of catchments across the world to undertake the first, truly global scale analysis of trends in river flows using undisturbed catchments. With the support of international organisations, including WMO, UNESCO and IPCC, ROBIN will lay the foundations for an enduring network of catchments, and scientists, to support global trend assessments in the future.
The influence of a dense network of small reservoirs on drought evolution in a semiarid region 
Authors: Ribeiro Neto Germano , Colombo Paolo , Cavalcante Louise , Kchouk Sarra , Melsen Lieke , Cunha Costa Alexandre , W. Walker David , Martins Eduardo , van Oel Pieter
Published: September 2022

The rampant construction of reservoirs can cause a concentration of water in certain regions and scarcity in others. This gives rise to conflicts and social pressure to build more reservoirs, creating a vicious cycle. An example of this is Ceará, a  Brazilian state often affected by intense drought events. State-level water resources management is mainly focused on the administration of 155 public “strategic reservoirs”. There is also a Dense Network of (non-strategic) Reservoirs (DNR) formed by almost 107,000 dams that are informally constructed to unknown specifications, unmonitored, and their management is not aligned with the state and watershed level governance. The occurrence of a multi-year drought (2012-2020) revealed that a DNR can play a significant role in the evolution and intensification of drought events. We aimed to analyze this effect in the Banabuiu River basin from a socio-hydrological perspective. We modeled two scenarios through a mesoscale semi-distributed hydrological model for semi-arid regions (WASA): 1) simulating the current configuration of the hydrological system and 2) simulating a condition without the DNR. To explore the DNR effect on drought events, we used the novel Drought Cycle Analysis method (DCA) which combines the Standardized Precipitation Index (SPI) with the Volume Deficit information (VD, deviation of half of the total capacity of the monitored reservoirs). We also conducted interviews with smallholder farmers who are the main users of non-strategic reservoirs to understand the societal impact of these structures. Our results showed that the presence of the DNR advances the transition from meteorological towards hydrological drought and leads to slower recharge of the strategic reservoirs between and during drought events. On the other hand, farmers explained their water security has increased after having a non-strategic reservoir on their land. The interviews also revealed that non-strategic reservoirs are the primary water source for most farmers. Although there are other options for accessing water during multi-year drought events, these generally cannot meet the farmer's water demands, thus causing a reduction in their productive activity .
Distributed database technologies for citizen science and data sovereignty
Authors: Malard-Adam Julien , Sheejakumar Ki. , Harms Joel , Medema Wietske
Published: September 2022

Citizen science has a strong potential to contribute to the democratisation of science worldwide. In addition, such approaches can lead to the creation of “living” datasets that evolve over time, even in regions where few hydrological instruments have been installed.

Citizen science approaches, however, do face a number of hurdles. One major challenge is the need for a central server to receive, manage and host the data contributed by volunteers; such servers require expert knowledge to configure and are also quite costly to maintain or rent over extended periods of time. These difficulties pose a challenge to the long-term financial sustainability of citizen science initiatives in the long term, especially after project funding has ceased. In addition, the centralisation of data on a server creates a very strong dependency for the participating communities; if their access to the internet is limited or costly, or if the server is not maintained after the end of the project, communities will be unable to contribute new data or even view and use previously contributed data.

In this context, distributed databases, such as Constellation, offer a different approach. In these systems, every device (phone or computer) that contributes data to or reads data from the network is a client and sever in its own right and can store and transmit community data to other participants in the network, all without the need for a central server. The low barrier to entry and absence of server costs allows such networks to be rapidly developed and deployed with minimal budgets, all while becoming stronger and more resilient as they grow in popularity and users. In the African context, such an approach may contribute to wider adoption of citizen science tools and projects, as well as to better data sovereignty and sustainability.
Assessing drought risk to track progress in drought adaptation, mitigation and management at the global scale
Authors: Barker Lucy , Rickards Nathan , Sarkar Sunita , Hannaford Jamie , Magee Eugene , Rees Gwyn
Published: September 2022

Droughts are known to be one of the most damaging and costly natural hazards as a result of their large spatial scale, creeping nature and long duration. They have widespread primary and secondary impacts, and as such, proactive drought management is crucial to mitigate those impacts. In order to do so, it is crucial to understand the drought risk – i.e. the characteristics of the drought hazard, who or what is exposed to the drought hazard, and who (or what) is vulnerable to the effects of drought. Drought mitigation is one of five strategic objectives under the United Nations Convention to Combat Desertification (UNCCD) 2018-2030 Strategic Framework, under which a monitoring framework and a range of indicators was agreed by country Parties to the UNCCD.

Here we present new guidance created to help Parties to the UNCCD report on their progress towards Strategic Objective 3 ‘To mitigate, adapt to, and manage the effects of drought in order to enhance resilience of vulnerable populations and ecosystems’. Progress is monitored using three indicators, capturing the three fundamental components of risk: drought hazard, exposure to drought and vulnerability to drought. The three indicators, as agreed by Parties to the UNCCD, are:

Trends in the proportion of land under drought over the total land area,

Trends in the proportion of the total population exposed to drought, and

Trends in the degree of drought vulnerability.

Acknowledging the need for global applicability, the methods recommended to calculate these three indicators balance state-of-the-art science with relative simplicity, whilst also meeting the requirements set out in official UNCCD Decisions, guidelines of the World Meteorological Organization, and where possible utilising datasets used for other reporting activities (e.g. the Sustainable Development Goals). The methods for each indicator are illustrated using contrasting case studies, highlighting the flexibility of the approaches recommended, as well as opportunities for the future of national reporting on drought risk.
Multiple scale conflicts over water security in a semi-arid river basin: Banabuiu River Basin, Ceara - Brazil
Authors: Cavalcante Louise , van de Ridder Esmee , van Oel Pieter , Dewulf Art , Kchouk Sarra , Ribeiro Neto Germano , Walker David , Martins Eduardo
Published: September 2022

Interactions between society and water systems are influenced by decisions at different levels, from local farmers to high-level policymakers. In drought contexts, an additional layer of complexity concerns uncertainties with regard to expected rainfall and drought durations. In semiarid northeast Brazil, the idea of ‘fight against drought’ for a long has been the dominant idea among policymakers aiming to deal with drought impacts. This idea prioritizes water-supply measures such as the construction of reservoirs for water storage and hydraulic infrastructures to promote water transfers.  

A polycentric governance lens is used to understand the interactions and influences of multiple governance systems with competitive and cooperative relationships over water resources. We analyzed the multiple scale challenges in water management in the Banabuiú basin in the state of Ceará, using minutes from official water committee meetings, and qualitative data from interviews conducted with smallholder farmers, field technicians and civil servants in November 2021.

Fieldwork interviews provided insights into conflicts of interest and prioritization of stakeholders involved in reservoirs' water management. Conflicts vary across scales and levels. On a river basin level, the over-reliance on water infrastructure contributed to a situation of conflict between irrigated farmers and urban users in the metropolitan region of Fortaleza. At the local level, conflicts exist between local communities depending on a reservoir and a state-level water-management organization, who decided to transfer water to a municipality located 25km away. Interviewees mentioned the government's decisions are “killing the river”. These cross-scale conflicts highlight the interdependencies between stakeholders and challenges in socio-hydrological systems.  
Are the thresholds of ecological flows established by the water management authorities aligneed with the natural regime of rivers in Mediterranean regions? 
Authors: Aparicio Javier , Contreras Eva , Aguilar Cristina , Moreno Fátima , Polo María José
Published: September 2022

Maintaining ecological flow is a need for enviromental  sustainability of regulated rivers  in managed  water bodies, whatever the different and competitive water demands (urban supply, irrigation, energy, or ecology). This is a challenge that the hydropower sector has to deal with, in areas subjected to complex meteorology with long drought periods followed by intense flood episodes, like those affected by the Mediterranean climate, specially in run of river facilities. These facts point towards the introduction of new regulatory frameworks to push towards a minimum river flow regime more adapted to the naturally variable hydrological regime of streamflow in Mediterranean regions. This question is not trivial and this challenge becomes even more critical in a climate change scenario in which hydropower energy is markedly affected not only by the market but also  by a priori more extreme meteorological events. In this paper, the compliance of the minimum river flow regime established by the Water Authorities in ten water bodies with hydropower generation (6 run-of-river plants and 4 reservoir plants) in southern Spain has been analyzed using historical streamflow and reservoir inflow data series, respectively and assuming that these values  closely represent the natural regime upstream the hydropower plans. For each case, the compliance of ecological regime thresholds during the last 10 hydrological years (September 2010 - August 2020) was analyzed at daily scale. In addition,  an hourly scale analysis was added when hourly data series were available. The results obtained showed that the natural regime of the watercourses hardly complies with the conditions established in the state law on compliance with ecological flows in all of the cases, and that, therefore, these flows were oversized. This overestimation is extremely unbalanced in some of the bodies studied, as in the case of the Cala reservoir, where even a reduction of 90% of the ecological flow, cannot be met by one of the 4 conditions on more than 60% of occasions.

The results highlight the needs for a balanced and updated environmental flow regime in regions with large natural variability in order to support the sustainability of hidropower, especially in run of river facilities.
Using NDVI as an indicator of snowmelt runoff in Mediterranean mountain catchments: application to the Guadalfeo river basin, Sierra Nevada.
Authors: Torralbo Pedro , Pimentel Rafael , Herrero Javier , Aguilar Cristina , Moreno Fátima , Polo María José
Published: September 2022

In Mediterranean high mountain environments, the snow accumulation/melting regime determines the surface water balance, redistributing the fractions of infiltration/runoff and evaporation from the ground and conditioning the volume circulating in the river channels. Therefore, the snow cover adds another degree of complexity to the precipitation-flow relationships in these systems (e.g., rain-on-snow events). Thus, a process-oriented approach is necessary when studying these relationships.

The definition of indicators derived from satellite remote information is a widespread technique in the characterization of the hydrological state of a basin. Previous studies in these areas have identified the state of vegetation, through its vigorousness using the NDVI (Normalized Difference Vegetation Index), as a good indicator for the characterization of soil water content at the beginning of the hydrological year (Gómez-Giráldez et al., 2014).

Therefore, in this context, the objective of this study is to analyze the relationships between changes in the state of watershed vegetation and flow variations in snow-influenced watersheds as additional information to anticipate downstream seasonal inputs using previous remote sensing information. For this purpose, a 20-year series of daily flow rates at a gauged point in the Guadalfeo river basin, one of the headwater catchments of the Sierra Nevada National and Natural Paro river was used, together with meteorological time series and the simulation of snowpack water flows using the physical-based model SNOWMED. Hence, two flow events are selected: i) rainfall-runoff events and ii) melt-runoff events. The vegetation dynamics in the basin is analyzed through variations of NDVI, derived from Landsat data (TM and ETM+) during the same study period.

From the analysis, the lags between the local change in NDVI, the loss of snow-covered area at the headwaters and the occurrence of melt or mixed flow events allow us to establish the onset of the generalized melt state in the basin, as well as to estimate threshold antecedent states. The results deepen the understanding of the hydrological dynamics in the basin, as well as the capacity of the NDVI as a tracer of the hydrographs associated with the generalized states of melting in Mediterranean mountain basins.
Investigating hydrological and geomorphological functioning of the mysterious endemic Palmiet wetlands in South Africa. 
Authors: Tanner Jane , Smith Caitlin , Ellery Fred , Glenday Julia
Published: September 2022

Palmiet wetlands in South Africa perform a range of supporting, and regulating ecosystem services, including hydrological benefits such as flood attenuation and sustaining baseflows. Despite their importance in regulating the highly seasonal and somewhat flash flood type nature of the region’s hydrology, there remains uncertainty around the reasons for their occurrence in such a limited geographical extent (Eastern and Western Cape). Prionium serratum (Palmiet) is a robust perennial plant that is endemic to wetlands in the sandstones and quartzites of the Table Mountain Group (TMG). Palmiet wetlands are collapsing across the distributional range of this species, largely as a consequence of gully erosion that may or may not have been initiated by human activities.

Despite large investments by the State in restoration, serious knowledge gaps in our understanding of Palmiet wetland structure and function remain. This project identified that palmiet wetlands are sustained by significant amounts of sub-surface water (groundwater and interflow) moving through preferential flow paths in the alluvial fans, which are in turn sustained by groundwater discharge from the surrounding sandstones of the TMG. This conceptual model indicates that a consistent water supply is a palmiet system driver and a key component of palmiet wetland formation. The wetlands clearly retain a significant amount of water, leading to the maintenance of prolonged flows, and a larger baseflow, however the wetland is present due to the existence of the low flows and is not the primary driver of prolonged flows in the system. The work further identified the palmiet plants ability to control water loss through stomatal control, with highly variable but predictable responses to the localised climate systems apparent.

Geomorphology is another clear system driver. This aspect of the study showed that gully erosion leads to longitudinal slope reduction and valley widening in ways that can lead to wetland formation. Dating of sediment from these gullies identified sediment ages of 470 and 7060 BP indicating that these gullies were a part of system functioning prior to the introduction of European farming. The erosion was identified as key to establishing new wetland habitats downstream of the eroded wetland reach.
In search of catchment-scale hydrological laws: learning from the long-term water balance formulas
Authors: Andréassian Vazken , Sari Tewfik , Santos Léonard , de Lavenne Alban
Published: September 2022

In our search for emergent catchment-scale hydrological laws, we discuss here how a class of widely-used water-balance formulas (Turc-Mezentsev and Tixeront-Fu) were conceived by their authors more than 60 years ago. Because these water balance formulas deal with long-term quantities, we discuss various attempts to downscale them temporally, and progressively integrate mathematical formulations able to account for both the short-term (seasonnal) and long-term (multi-year) hydrologial memory observed in catchment systems.

References

 Fu, B.: On the calculation of the evaporation from land surface, Atmos. Sin., 5, 23–31, 1981. 

Mezentsev, V.: Back to the computation of total evaporation, Meteorologia i Gidrologia, 5, 24–26, 1955. 

Tixeront, J.: Prediction of streamflow (in French: Prévision des apports des cours d'eau), in: IAHS publication no. 63: General Assembly of Berkeley, IAHS, Gentbrugge, 118–126, available at: http://hydrologie.org/redbooks/a063/063013.pdf (last access: 1 May 2019), 1964. 

 Turc, L.: The water balance of soils: relationship between precipitations, evaporation and flow (in French: Le bilan d'eau des sols: relation entre les précipitations, l'évaporation et l'écoulement), Annales Agronomiques, Série A, IV, 491–595, 1954.
Comparison and validation of outputs from global hydrological models against local hydrological data in South Africa
Authors: Okal Harriette , Tanner Jane , Hughes Denis
Published: September 2022

Study aim: To test the performance of 7 global hydrological models against local South African datasets from the Earth2Observe platform in terms of the monthly water balance estimation.

Methodology: The remotely-sensed global forcing datasets tested are actual evapotranspiration (ET) and runoff provided by Earth2Observe models. The local datasets were retrieved from the Water Resources of South Africa (WR2012) database, which quantifies the water resources of South Africa, Lesotho and Swaziland per quaternary catchment. The Quaternary Catchments consist of the lowest and most detailed level of operational catchment in the Department of Water and Sanitation (DWS), South Africa. An assessment of outputs between WR2012 and the ensemble outputs available to download from the seven Earth2Observe models (CEH, CNRS, UNIVK, UNIVU, METFR, JRC, and ECMWF) was conducted in South Africa. The mean annual runoff (MAR) time series analysis for the WR2012 and the Earth2Observe models were calculated. The Percentage of Bias (PoB) of each of the seven models with respect to the WR2012 data were computed as: %bias = (MARi - MARWR) x 100/ MARWR.

Results: Models JRC, UNIVU, and CNRS showed excessive bias values in large areas while the remaining four models generally exhibited large negative bias values, but with high positive values in the extreme Northeast and the dry areas of the country. The wetter regions of the country (Eastern Cape and KwaZulu Natal) displayed consistent results across all models. Apart from CNRS, all the results have an approximate water balance (precipitation = evapotranspiration + runoff). This is largely due to compensating over or under estimation of both precipitation and evapotranspiration.

Conclusion and Recommendations: The seven models are therefore rendered unreliable for water balance information in South Africa. Additionally, this study shows that ET data from the Earth2Observe platform is reliable to use, but the global runoff datasets should not be used in South Africa. It is recommended that organisations responsible for the generation of these global datasets issue warnings that these outputs have not been validated thus cannot be relied on.
Quantifying the uncertainty associated with future floods simulations from regional climate models
Authors: Ajjur Salah Basem , Al-Ghamdi Sami G.
Published: September 2022

This study is motivated by showing how future floods predictions in arid areas respond to uncertainty in climatic parameters—a question, if explored, that bridges a gap in water resources management plans. To address this question, we projected the changes, over Qatar, in four climatic parameters (surface air temperature, precipitation, wind speed, and potential evapotranspiration) from eight Regional Climate Models (RCMs) under two Representative Concentration Pathways (RCP4.5 and RCP8.5) during the middle of the 21st century (2031–2050). Using topographic and groundwater data, a physically-based water balance model was built to simulate future floods under all these scenarios. Findings show high uncertainty in climatic parameters. Relative to the historical period, values varied under RCP4.5 (RCP8.5) from +1.8 to +3.4 (+3.8 to +5.6)°C for average temperature, -48% to +15% (-60% to +6%) for annual precipitation, -0.23 to +0.1 (-0.27 to +0.04) m/hour for wind speed, and from -5.7 to +12.8 (+4.3 to +17) mm for annual potential evapotranspiration. Uncertainty in climatic parameters caused significant uncertainty in future floods estimations. During the middle of the 21st century, floods simulations varied from -67% to +64% with an average value of -20% under RCP4.5, and from -81% to +8% with an average value of -36% under RCP8.5. The greatest uncertainty resulted from the driving models, whereas the choice of emission scenario had a secondary impact. Since floods studies are critical to save lives and assets, the study’s findings emphasize the importance of both considering the uncertainty associated with climatic parameters and the regional climatic information chosen.
Restoring instream wood as a Nature-based Solution to nutrient pollution
Authors: Howard Ben , Baker Ian , Kettridge Nick , Ullah Sami , Krause Stefan
Published: September 2022

Nutrient pollution is among the biggest water quality challenges facing environmental engineers, causing ecosystem health decline and requiring significant treatment before water is safe for human use. The remediation of nutrient pollution can occur along the river corridor where nutrients can be retained and transformed to environmentally benign products (e.g. N2) by microbially mediated reactions. Catchment mismanagement, especially the removal of wood from channels, has reduced the capacity of rivers to fulfil this function, limiting reactions by two primary mechanisms: transport and reaction kinetics. These limitations could be abated by restoring rivers with instream wood, thereby providing a Nature-based Solution to this persistent water quality challenge.

Little research has directly investigated the potential of wood introductions to increase nutrient transformations in the river corridor. Here, we present results on two linked experiments which investigated the transport and reaction kinetics of nutrients at different scales.

The transport limitation refers to the total flux of water into the hyporheic zone, a hotspot of biogoechemistry in the river sediment, and its residence time therein. Instream wood causes an obstacle for river flow which could induce hyporheic exchange of suitable properties to allow favourable nutrient transformations. To investigate this, we installed wood features in a lowland stream in the UK and conducted a series of smart tracer injections to estimate (metabolically active) transient storage using a powerful before-after-control-intervention experimental design.

The reaction kinetic limitation refers especially to the availability and quality of organic matter, which could be improved by wood decomposition. An incubation experiment investigates the potential of instream wood as a source of organic matter and the effect of this on nutrient transformation rates and greenhouse gas production.

Preliminary analysis suggests that wood is effective at increasing nutrient transformations in both mechanisms. In the incubation experiment, nutrient transformation rates were higher in systems with wood compared to those without. In the field experiment, more metabolically active transient storage was observed in the sub-reach where restoration features had been installed. Our results provide evidence for the effectiveness of wood in river restoration and the efficacy of Nature-based Solutions for water quality challenges.
Quantitative Microbiological Risk Assessment of drinking water produced in Ouagadougou, Burkina Faso
Authors: Sossou Seyram , Bidi Francois-Cedry , Ouattara Bernadette , Kabre Elie
Published: September 2022

Drinking of safety water is of utmost importance for the good health of communities. Over years, in addition to tap water there has been an increase in the consumption of water packaging in bottles and sachets by the populations in Sahelian Africa.  This study aimed at assessing the safety of tap, bottle and sachet water produced and consumed in Ouagadougou, the capital city of Burkina Faso. A site inspection of the packaged water production units was carried out to assess the process and conditions for their production. The evaluation of water quality was made through household surveys by questionnaire according to the consumer and key informant interview. For assessing microbiological quality, a total of 330 samples water (including 257 packaged sachet water, 41 bottle water and 32 tap water) were submitted for laboratory analysis. With QMRA method, a quantitative estimate of the microbiological risk was carried out. The results showed a similar process and hygienic practices for the production of drinking water in Ouagadougou. However, possible hazardous events were found in the sachet water production units which may compromise water quality. The results of surveys have shown that, for all surveyed, the water produced at the tap and in the bottle is of good quality. While, for 49,52% of consumers packaged sachet water is not good quality. This opinion is confirmed by laboratory analyzes according to which 23% of the samples water in sachets do not comply with the standard respectively, do not comply with both Burkina Faso and WHO standard. Compared to the disease burden by Cryptosporidium parvum (7,37.10-7 DALY), the disease burden by Escherichia coli O157: H7 (1,42.10-1 DALY) and by rotavirus (4,79.10-3 DALY) are higher and exceed the reasonable level of reference risk established by WHO (10-6 DALY). Based on these, appropriate mitigation and monitoring were proposed for action in sachet water production units. This study will allow decisions to be made on the treatment and robust hygienic conditions for producing drinking water in Ouagadougou, Burkina Faso.
A wavelet analysis of surface water – groundwater interaction in reaches affected by hydropeaking
Authors: Chiogna Gabriele , Basilio Hazas Monica , Marcolini Giorgia , Singh Tanu , Wohlmuth Barbara
Published: September 2022

The management of hydropower plants influences the variations in the discharge of the rivers, introducing for example weekly fluctuations. This variability can in turn influence the interaction between surface water and groundwater. In our work, we analyse an alpine area in Trentino in northern Italy, where four different river sections are considered. The four reaches (Noce, Adige before the confluence with the Noce, Adige after the confluence with the Noce, Avisio) are differently affected by reservoir operation. We hence study the influence of surface water management on the aquifer by using a transient model built with Modflow-OWHM for the hydrological years 2009/10 and 2016/17, where the year 2016/17 was characterised by particularly low amount of precipitation. The results were interpreted using continuous wavelet analysis and wavelet coherence analysis. In particular, we focused on the non-stationary weekly variations observed in the groundwater table. Such fluctuations are very pronounced near the river sections affected by reservoir operation. Moreover, the comparison of the behaviour in 2009/10 and in 2016/17 shows that the weekly variations are stronger in dry years than in wet years. Nevertheless, the proportion of the aquifer that shows a strong weekly variability remains similar. The water budget along the four river sections does not change significantly in the two hydrological years considered. However, our wavelet analysis shows that in 2016/17 a strong weekly variability is observed in surface water-groundwater exchange while in 2009/10 this dynamic is not observed.
Simulating nitrate loads and concentrations in the main French rivers by 2050 according to different territorial agricultural scenarios.
Authors: Casquin Antoine , Billen Gilles , Silvestre Marie , Garnier Josette , Thieu Vincent
Published: September 2022

In excess compared to the other major nutrients, nitrogen (N) ­-transported mainly in the form of nitrates- from land surfaces to coastal areas, is responsible for harmful algal blooms in coastal areas. In France, most of the water loads of N transferred to the sea comes from fertilization on agricultural surfaces and their highly leached surpluses. The distance between the sources of nutrients and the manifestations of eutrophication is one of the difficulties encountered in reducing coastal eutrophication. The present study, which aims to model the N cascade at a national scale, for the current situation and according to different agricultural/dietary scenarios, is a basis for discussion with river-basin managers, who are required to enforce the Marine Strategy Framework Directive that sets the conditions for good status of marine environments.

Current N surpluses (2015-2018) are calculated via the GRAFS (Generalized Representation of the Agro-Food System), method (Le Noe et al. 2017), at the NUTS-2 scale (French regions) for arable land, permanent grassland and permanent crops. An approach based on yearly run-off coupled with a riparian denitrification routine allows linking these surpluses to average baseflow/quickflow concentrations in elementary catchments (average size: 5.8 km2). These diffuse lateral inputs, plus point-source inputs, are then integrated into the pyNuts-Riverstrahler modelling platform (Billen et al. 1994, Raimonet et al. 2019), which calculates nitrogen transformations and transfers along the river network. The model outputs have a kilometric spatial resolution and a 10 days temporal resolution, making it possible to finely represent the spatio-temporal variability of N concentrations and loads on the French territory.

Different plausible scenarios for the future of the agro-food system in France, with a gradient of territorial specialisation/N intensities, are then modelled within the GRAFS-pyNuts-Riverstrahler approach to assess their impacts on the N cascade at the national scale. This study is part of the Nuts-STeauRY project (funded by the OFB: https://nuts-steaury.cnrs.fr/), which aims to demonstrate the contribution of integrated land-sea modelling to the realisation of spatialized scenarios to limit coastal eutrophication in France. Carbon, phosphorus and dissolved silica will also be modelled for this project.

Billen2014:10.1007/BF00007414

LeNoë2017:10.1016/j.scitotenv.2017.02.040

Raimonet2019:10.3389/fmars.2018.00136