Thomas Stieglitz

Centre National de la Recherche Scientifique

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Bruno Hamelin

Centre de Recherche et d’Enseignement de Géosciences de l’Environnement

Pierre Deschamps

Centre de Recherche et d’Enseignement de Géosciences de l’Environnement

Pierre Séraphin

Centre de Recherche et d’Enseignement de Géosciences de l’Environnement

Yves Morel

Hospices Civils de Lyon

Olaègbè Victor Okpeitcha

Université d'Abomey-Calavi

Thomas Duhaut

Centre National de la Recherche Scientifique

Julio Gonçalvès

Centre National de la Recherche Scientifique

Zacharie Sohou

Institut National des Recherches Agricoles du Bénin

Arnaud Assogba

Institut National des Recherches Agricoles du Bénin

Alexis Chaigneau

Université d'Abomey-Calavi

Cooperative Institutions

Centre National de la Recherche Scientifique

Institut de Recherche pour le Développement

Laboratoire d’Études en Géophysique et Océanographie Spatiales

Université de Toulouse

Université Toulouse III - Paul Sabatier

University of Douala

Université d'Abomey-Calavi

Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement

Centre de Recherche et d’Enseignement de Géosciences de l’Environnement

Aix-Marseille Université

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review for egusphere-2022-22 by Seraphin et al.

Pierre Séraphin Julio GonÃ§alvÃ ̈s Bruno Hamelin Thomas Stieglitz Pierre Deschamps

This study assesses the detailed water budget of the Saq-Ram Aquifer System (520 000 km2) over the 2002–2019 period using satellite-gravity data from the Gravity Recovery And Climate Experiment (GRACE). The three existing GRACE solutions (JPL, CSR, GSFC) were tested for their local compatibility to compute groundwater storage variations in combination with soil moisture datasets (VIC, CLSM, NOAH) available from the Global Land Data Assimilation System (GLDAS) land surface models. Accounting for groundwater pumping (15.7 ± 1.1 mm yr-1), artificial recharge (2.2 ± 0.8 mm yr-1) and natural discharge (0.3 ± 0.06 mm yr-1) uniformly distributed over the Saq-Ram domain, the GRACE-derived water mass balance calculation yields a long-term estimate of the domain-averaged natural recharge of 2.4 ± 1.4 mm yr-1, corresponding to 4.4 ± 2.6 % of the annual average rainfall. Beyond the global approach proposed here, spatial heterogeneities regarding the groundwater recharge were identified. The first source of heterogeneity is of anthropogenic origin. Within agricultural plots, irrigation excess is great enough to artificially recharge the aquifer (i.e. 167 ± 83 mm yr-1 distributed over irrigated areas). However, on the outskirts of these crop areas subjected only to the natural recharge but still influenced by pumping drawdown, there is a risk of relative disconnection from the infiltration front with the declining water table (i.e. the unsaturated zone thickens faster than percolation flows through it), making effective recharge locally zero. The second source of recharge heterogeneity identified here is natural: Volcanic lava deposits (called Harrats on the Arabian Peninsula) which cover 8 % of the Saq-Ram Aquifer domain but contribute to more than 50 % of the total natural recharge. Hence, in addition to this application on the Arabian Peninsula, this study strongly indicates a major control of geological context on arid aquifer recharge which has been poorly discussed hitherto.

Infiltration (HVAC)

10.5194/egusphere-2022-22-rc2

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Influence of intensive agriculture and geological heterogeneity on the recharge of an arid aquifer system (Saq-Ram, Arabian Peninsula)

Pierre Séraphin Julio Gonçalvès Bruno Hamelin Thomas Stieglitz Pierre Deschamps

Abstract. This study assesses the detailed water budget of the Saq-Ram Aquifer System (520 000 km2) over the 2002–2019 period using satellite-gravity data from the Gravity Recovery And Climate Experiment (GRACE). The three existing GRACE solutions (JPL, CSR, GSFC) were tested for their local compatibility to compute groundwater storage variations in combination with soil moisture datasets (VIC, CLSM, NOAH) available from the Global Land Data Assimilation System (GLDAS) land surface models. Accounting for groundwater pumping (15.7 ± 1.1 mm yr-1), artificial recharge (2.2 ± 0.8 mm yr-1) and natural discharge (0.3 ± 0.06 mm yr-1) uniformly distributed over the Saq-Ram domain, the GRACE-derived water mass balance calculation yields a long-term estimate of the domain-averaged natural recharge of 2.4 ± 1.4 mm yr-1, corresponding to 4.4 ± 2.6 % of the annual average rainfall. Beyond the global approach proposed here, spatial heterogeneities regarding the groundwater recharge were identified. The first source of heterogeneity is of anthropogenic origin. Within agricultural plots, irrigation excess is great enough to artificially recharge the aquifer (i.e. 167 ± 83 mm yr-1 distributed over irrigated areas). However, on the outskirts of these crop areas subjected only to the natural recharge but still influenced by pumping drawdown, there is a risk of relative disconnection from the infiltration front with the declining water table (i.e. the unsaturated zone thickens faster than percolation flows through it), making effective recharge locally zero. The second source of recharge heterogeneity identified here is natural: Volcanic lava deposits (called Harrats on the Arabian Peninsula) which cover 8 % of the Saq-Ram Aquifer domain but contribute to more than 50 % of the total natural recharge. Hence, in addition to this application on the Arabian Peninsula, this study strongly indicates a major control of geological context on arid aquifer recharge which has been poorly discussed hitherto.

Water balance

10.5194/egusphere-2022-22

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Citations (1)

Seasonal and interannual variations of suspended particulate matter in a West-African lagoon (Nokoué lagoon, Benin): Impact of rivers and wind

Estuarine Coastal and Shelf Science (2024)

Indrig Laeticia Ntangyong Alexis Chaigneau Yves Morel Arnaud Assogba Olaègbè Victor Okpeitcha

Discharge

10.1016/j.ecss.2024.108821

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Citations (2)

The Role of Space-Based Observations for Groundwater Resource Monitoring over Africa

Surveys in Geophysics (2023)

Anne Springer Téodolina Lopez Michael Owor Frédéric Frappart Thomas Stieglitz

Abstract Africa is particularly vulnerable to climate change impacts, which threatens food security, ecosystem protection and restoration initiatives, and fresh water resources availability and quality. Groundwater largely contributes to the mitigation of climate change effects by offering short- to long-term transient water storage. However, groundwater storage remains extremely difficult to monitor. In this paper, we review the strengths and weaknesses of satellite remote sensing techniques for addressing groundwater quantity issues with a focus on GRACE space gravimetry, as well as concepts to combine satellite observations with numerical models and ground observations. One particular focus is the quantification of changes in groundwater resources in the different climatic regions of Africa and the discussion of possible climatic and anthropogenic drivers. We include a thorough literature review on studies that use satellite observations for groundwater research in Africa. Finally, we identify gaps in research and possible future directions for employing satellite remote sensing to groundwater monitoring and management on the African continent. Article Highlights Overview on the distribution and characteristics of African groundwater resources including future projections Combination of satellite and in situ observations with numerical models allows us to obtain a synoptic view of groundwater-related processes Summary of current concepts and achievements of satellite remote sensing-based groundwater monitoring and decision making over Africa

10.1007/s10712-022-09759-4

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Application of Shore-Based Video and Unmanned Aerial Vehicles (Drones): Complementary Tools for Beach Studies

Remote Sensing (2020)

Donatus Bapentire Angnuureng Philip‐Neri Jayson‐Quashigah Rafaël Almar Thomas Stieglitz Edward J. Anthony

Video camera systems have been used over nearly three decades to monitor coastal dynamics. They facilitate a high-frequency analysis of spatiotemporal shoreline mobility. Video camera usage to measure beach intertidal profile evolution has not been standardized globally and the capacity to obtain accurate results requires authentication using various techniques. Applications are mostly site specific due to differences in installation. The present study examines the accuracy of intertidal topographic data derived from a video camera system compared to data acquired with unmanned aerial vehicle (UAV, or drone) surveys of a reflective beach. Using one year of 15-min video data and one year of monthly UAV observations, the intertidal profile shows a good agreement. Underestimations of intertidal profile elevations by the camera-based method are possibly linked to the camera view angle, rectification and gaps in data. The resolution of the video-derived intertidal topographic profiles confirmed, however, the suitability of the method in providing beach mobility surveys matching those required for a quantitative analysis of nearshore changes. Beach slopes were found to vary between 0.1 and 0.7, with a steep slope in May to July 2018 and a gentle slope in December 2018. Large but short-scale beach variations occurred between August 2018 and October 2018 and corresponded to relatively high wave events. In one year, this dynamic beach lost 7 m. At this rate, and as also observed at other beaches nearby, important coastal facilities and infrastructure will be prone to erosion. The data suggest that a low-cost shore-based camera, particularly when used in a network along the coast, can produce profile data for effective coastal management in West Africa and elsewhere.

Drone

Coastal erosion

10.3390/rs12030394

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Citations (43)

Seasonal to decadal scale shoreline changes along the Cameroonian coastline, Bay of Bonny (1986 to 2020)

Regional Studies in Marine Science (2021)

Njutapvoui F. Nourdi Raphaël Onguéné Abessolo O. Grégoire Jean-Paul Rudant Sakaros Bogning

Anomaly (physics)

10.1016/j.rsma.2021.101798

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Conceptual uncertainties in groundwater and porewater fluxes estimated by radon and radium mass balances

Limnology and Oceanography (2021)

Valentí Rodellas Thomas Stieglitz Joseph Tamborski Pieter van Beek Aladin Andrisoa

Abstract Radium isotopes and radon are routinely used as tracers to quantify groundwater and porewater fluxes into coastal and freshwater systems. However, uncertainties associated with the determination of the tracer flux are often poorly addressed and often neglect all the potential errors associated with the conceptualization of the system (i.e., conceptual uncertainties). In this study, we assess the magnitude of some of the key uncertainties related to the determination of the radium and radon inputs supplied by groundwater and porewater fluxes into a waterbody (La Palme Lagoon, France). This uncertainty assessment is addressed through a single model ensemble approach, where a tracer mass balance is run multiple times with variable sets of assumptions and approaches for the key parameters determined through a sensitivity test. In particular, conceptual uncertainties linked to tracer concentration, diffusive fluxes, radon evasion to the atmosphere, and change of tracer inventory over time were considered. The magnitude of porewater fluxes is further constrained using a comparison of independent methods: (1) 224 Ra and (2) 222 Rn mass balances in overlying waters, (3) a model of 222 Rn deficit in sediments, and (4) a fluid‐salt numerical transport model. We demonstrate that conceptual uncertainties are commonly a major source of uncertainty on the estimation of groundwater or porewater fluxes and they need to be taken into account when using tracer mass balances. In the absence of a general framework for assessing these uncertainties, this study provides a practical approach to evaluate key uncertainties associated to radon and radium mass balances.

TRACER

Radium

Submarine groundwater discharge

10.1002/lno.11678

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Citations (63)

Comment on egusphere-2022-22

Pierre Séraphin Julio GonÃ§alvÃ ̈s Bruno Hamelin Thomas Stieglitz Pierre Deschamps

Infiltration (HVAC)

10.5194/egusphere-2022-22-rc1

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Comment on egusphere-2022-22

Pierre Séraphin Julio Gonçalvès Bruno Hamelin Thomas Stieglitz Pierre Deschamps

Abstract. This study assesses the detailed water budget of the Saq-Ram Aquifer System (520 000 km²) over the 2002–2019 period using satellite-gravity data from the Gravity Recovery And Climate Experiment (GRACE). The three existing GRACE solutions (JPL, CSR, GSFC) were tested for their local compatibility to compute groundwater storage variations in combination with soil moisture datasets (VIC, CLSM, NOAH) available from the Global Land Data Assimilation System (GLDAS) land surface models. Accounting for groundwater pumping (15.7 ± 1.1 mm yr^-1), artificial recharge (2.2 ± 0.8 mm yr^-1) and natural discharge (0.3 ± 0.06 mm yr^-1) uniformly distributed over the Saq-Ram domain, the GRACE-derived water mass balance calculation yields a long-term estimate of the domain-averaged natural recharge of 2.4 ± 1.4 mm yr^-1, corresponding to 4.4 ± 2.6 % of the annual average rainfall. Beyond the global approach proposed here, spatial heterogeneities regarding the groundwater recharge were identified. The first source of heterogeneity is of anthropogenic origin. Within agricultural plots, irrigation excess is great enough to artificially recharge the aquifer (i.e. 167 ± 83 mm yr^-1 distributed over irrigated areas). However, on the outskirts of these crop areas subjected only to the natural recharge but still influenced by pumping drawdown, there is a risk of relative disconnection from the infiltration front with the declining water table (i.e. the unsaturated zone thickens faster than percolation flows through it), making effective recharge locally zero. The second source of recharge heterogeneity identified here is natural: Volcanic lava deposits (called Harrats on the Arabian Peninsula) which cover 8 % of the Saq-Ram Aquifer domain but contribute to more than 50 % of the total natural recharge. Hence, in addition to this application on the Arabian Peninsula, this study strongly indicates a major control of geological context on arid aquifer recharge which has been poorly discussed hitherto.

Infiltration (HVAC)

10.5194/egusphere-2022-22-rc3

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Citations (0)

The 21st August 2020 Flood in Douala (Cameroon): A Major Urban Flood Investigated with 2D HEC-RAS Modeling

Water (2022)

Junior Yves-Audrey Iroume Raphaël Onguéné Francis Djanna Koffi Antoine Colmet-Daage Thomas Stieglitz

A major flood event occurred on 21 August 2020 in the densely populated Makèpè Missokè neighborhood in the city of Douala (Cameroon, Africa). Nearly 2210 buildings and 12,376 victims spread over 82 hectares were affected. A 2D HEC-RAS model is applied to simulate and characterize this event. A cross analysis of flood depth and flow velocity is used to classify the flood risk and identify areas exposed from low to high hazard. The simulations provide detailed information on the flood characteristics (extent, depth, velocity, arrival time, and duration). The simulated maximum water surface profiles are consistent with the floods marks with differences ranging from 0.02 m to 0.44 m, indicating a good agreement between the observed and simulated water levels at the peak flow (NSE = 0.94, Erel = 0.92, RMSE = 0.21 m). The maximum inundation level is 4.48 m and the flow velocity is globally low at less than 1 m/s. The average flood arrival time and duration are 5 h and 26 h, respectively, for a threshold height of 0.5 m. These results indicate a fast mobilization of the major river channel for the evacuation of this flood. The level of accuracy of the developed model of the 21 August 2020 flood event is appropriate for flood hazard assessment in the city of Douala and is designed to find operational application in future events.

Arrival time

10.3390/w14111768

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Citations (23)