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3. Drought-induced regime shift and resilience of a Sahelian ecohydrosystem

Author

Wendling, Valentin, Peugeot, Christophe, Mayor, Ángeles Garcia, Hiernaux, Pierre, Mougin, Eric, Grippa, Manuela, Kergoat, Laurent, Walcker, Romain, Galle, Sylvie, Lebel, Thierry, Spatial Ecology and Global Change, Environmental Sciences, Hydrosciences Montpellier (HSM), Institut de Recherche pour le Développement (IRD)-Université Montpellier 2 - Sciences et Techniques (UM2)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Copernicus Institute for Sustainable Development, Utrecht University [Utrecht], Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Ecologie Fonctionnelle et Environnement (ECOLAB), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées, Laboratoire d'étude des transferts en hydrologie et environnement (LTHE), Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique de Grenoble (INPG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD)-Université Montpellier 2 - Sciences et Techniques (UM2)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Laboratoire Ecologie Fonctionnelle et Environnement (LEFE), Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT), Spatial Ecology and Global Change, and Environmental Sciences

Subjects
010504 meteorology & atmospheric sciences, rainfall, Climate change, alternative stable states, 010501 environmental sciences, 01 natural sciences, Alternative stable state, Soil retrogression and degradation, Sahel, Clearing, Ecosystem, Regime shift, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, General Environmental Science, 2. Zero hunger, regime shifts, rainfall variability, Renewable Energy, Sustainability and the Environment, variability, Public Health, Environmental and Occupational Health, Vegetation, 15. Life on land, 13. Climate action, Climatology, [SDE]Environmental Sciences, eco-hydrology, Environmental science, Surface runoff
Abstract

International audience; The Sahel (a semi-arid fringe south of the Sahara) experienced a long and prolonged drought from the1970s to the mid-1990s, with a few extremely severe episodes that strongly affected ecosystems andsocieties. Long-term observations showed that surface runoff increased during this period, despite therainfall deficit. This paradox stems from the soil degradation that was induced by various factors,either directly linked to the drought (impact on vegetation cover), or, in places, to human practices (land clearing and cropping). Surface runoff is still increasing throughout the region, suggesting that Sahelian ecohydrosystems may have shifted to a new hydrological regime. In order to explore this issue, we have developed a simple system dynamics model incorporating vegetation–hydrology interactions and representing in a lumped way the first order processes occurring at the hillslope scale and the annual timestep. Long term observations on a pilot site in northern Mali were used to constrain the model and define an ensemble of plausible simulations. The model successfully reproduced the vegetation collapse and the runoff increase observed over the last 60 years. Our results confirmed that the system presents two alternative states and that during the drought it shifted from a high-vegetation/low-runoff regime to the alternative low-vegetation/high-runoff one, where it has remained trapped until now. We showed that the mean annual rainfall deficit was sufficient to explain the shift. According to the model, vegetation recovery and runoff reduction are possible in this system, but the conditions in which they could occur remain uncertain as the model was only constrained by observations over the collapse trajectory. The study shows that the system is also sensitive to the interannual and decadal variability of rainfall, and that larger variability leads to higher runoff. Both mean rainfall and rainfall variability may increase in central Sahel under climate change, leading to antagonist effects on the system, which makes its resilience uncertain.

Published
2019

4. Small scale eco-hydrological regime shifts and impacts on regional changes in the Sahel.

Author

Wendling, Valentin, Peugeot, Christophe, Mayor, Angeles Garcia, Hiernaux, Pierre, Mougin, Eric, Walcker, Romain, Grippa, Manuela, Kergoat, Laurent, and Lebel, Thierry

Subjects
*ECOHYDROLOGY, *SMALL states, *WATER table, *FLOOD risk, *WATER supply, *RUNOFF, *LUNAR craters, *WATERSHEDS
Abstract

The West African Sahel experienced a long drought from the 1970s to the 1990s during which runoff has paradoxically increased, as a response to human and climate-induced changes in surface conditions. Despite the vegetation recovery (re-greening) observed at regional scale over the past 30 years, surface runoff is still increasing, suggesting that the Sahelian eco-hydrological system passed a tipping point and is now trapped in a « high runoff » state. To study this hypothesis, we developed a system dynamics model incorporating vegetation-hydrology interactions at annual time scale. The model successfully reproduced the vegetation collapse and the increase of runoff-prone bare soil areas monitored over 65 years on a pilot site in Northern Mali. Our results confirmed the existence of a tipping point between alternative high/low runoff states at the small catchment scale. According to the model, a reverse shift to the pre-drought low runoff state is possible, but the conditions in which this shift would occur remain uncertain. The system trajectory presents a strong sensitivity to annual rainfall variability (amplitude and temporal structure). This study suggests that the increasing runoff in a re-greening environment is caused by the tipping of some areas to a high runoff/low vegetation state, illustrating how a regime shift in sub-systems can result in eco-hydrological changes at larger scale. The associated large-scale changes of the rainfall partitioning may alter evapo-transpiration and thus the surface-atmosphere feed-back. Those changes also bear strong environmental and socio-economic consequences, either adverse (increase of degraded areas to the detriment of agriculture, and increased flood risk) or beneficial (increased water resource in ponds and water tables). [ABSTRACT FROM AUTHOR]

Published
2019

5. Einheit zur messung der sedimentationsgeschwindigkeit von partikeln in suspension in einem fluid und vorrichtung mit mindestens einer derartigen einheit und einem automatischen probennehmer

Author

Nicolas Gratiot, Bernard Mercier, Cédric Legout, Valentin Wendling, Catherine Coulaud, Hanri Mora, Wendling, Valentin, and Jeunes Chercheuses et Jeunes Chercheurs - Système de caractérisation des agrégats et des flocs dans les cours d'eau et rivières chargées - - SCAF2012 - ANR-12-JS06-0006 - JC - VALID

Subjects
[SDE] Environmental Sciences, [SPI] Engineering Sciences [physics], [SDU.STU.HY] Sciences of the Universe [physics]/Earth Sciences/Hydrology, [PHYS.MECA.MEFL] Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph]
Abstract

A unit for measuring the falling speed of particles in suspension in a fluid comprises a sealed container (6) having an opening (9) and defining an open compartment (15) comprising the opening and intended to contain the fluid, and a sealed compartment (16), sealing means separating the open compartment from the sealed compartment, and means for measuring the falling speed placed in the sealed compartment and comprising at least three electromagnetic radiation emitters distributed along a longitudinal axis (L) of the open compartment, each emitter being oriented according to a radiation axis crossing the open compartment at different heights along the longitudinal axis, an equal number of receivers distributed along the longitudinal axis, each receiver being placed in the radiation axis of a corresponding emitter, means for controlling the emitters and the receivers, and a system for acquiring data connected to the receivers, the acquired data being used to obtain the falling speed of the particles and the change of same as a function of the height in the open compartment and as a function of time, said change quantifying the flocculation of the particles.

Published
2015

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