Tipping points and regime shifts in dynamic systems : a new modeling approach to study Sahelian ecohydrology
The Sahel witnessed a climatic drought from the 1970s to the 2000s. During this period, vegetation cover decreased and surface runoff increased in many places. While annual rainfall has partly recovered since the begining of this century, runoff has not reacted accordingly. The state of the ecohydrological system changed, and it responds in a new way to similar forcings. This study aims to better understand these regime shifts : their modalities (abrupt or gradual changes), the involved processes, and their impact on the water cycle components.
System dynamics modeling is considered. The system (watershed) evolution under forcings (the climate) is modeled by a system of ordinary differential equations. This approach is common in theoretical ecology, but still little explored in hydrology. It allows representing regime shifts and studying their causes and consequences.
A model representing the dynamics of vegetation cover and runoff has been developed. The first order processes and their feedbacks (positive or negative) under the Sahelian climate are considered.
A first case study allowed to test the model on a tiger bush site in the Malian Gourma exhibiting very little anthropic forcing, and where observations exist since the 1950s. This site evolved from a vegetated and low runoff state before drought to a very low vegetated and high runoff state nowadays. Forced by the rainfall time series, the model allows, after calibration, to reproduce the observed regime shift and to characterize the tipping points (date, causes). The approach is then applied on other case studies to improve its reliability at the regional scale.
This study demonstrates the ability of system dynamics models to contribute to understand the instabilities in the Sahelien eco-hydrological functioning.
Publications :
Tipping points in hydrology: observed regional regime shift and System Dynamics modeling.
Wendling V., Peugeot C., Grippa M., Kergoat L., Mougin E., Hiernaux P., Rouché N., Panthou G., Rajot J.-L., Pierre C., Mora O., Garcia-Mayor A., Ba A., Lawin E., Bouzou-Moussa I.
EGU General Assembly 2022, Vienne, Autriche, 23–27 Mai 2022, session Nonlinear Dynamics and Tipping Points in the Earth System.
Tipping points in continental hydrology : developing a system dynamics approach to represent the interfaces in the critical zone and built a decade-scale hydrologic model.
Wendling V., Peugeot C., Grippa M., Panthou G., Rajot J.-L., Mora O., Garcia-Mayor A., Lawin E., Bouzou-Moussa I., Ba A., Demarty G., Etchanchu J., Hector B., Galle S., Lebel T and the TipHyc Project
XIth Scientific Assembly of the International Association of Hydrological Sciences (IAHS 2022), Montpellier (France), 29 May – 3 June 2022., session Unsolved Problems in Hydrology: Overarching session.
Assessing hydrological regime shifts through system-dynamics modeling.
Wendling V., Peugeot C., Grippa M., Panthou G., Rajot J.-L., Mora O., Garcia-Mayor A., Lawin E., Bouzou-Moussa I., Ba A., and the collaborators of the TipHyc Project
First OZCAR TERENO International Conference, Strasbourg, France 5 – 7 October 2021. session Challenges in understanding CZ processes in Africa.
Drought induced regime shift and resilience of a Sahelian eco-hydrosystem
Wendling V., Peugeot C., Garcia-Mayor A., Hiernaux P., Mougin E., Walcker R., Grippa M., Kergoat L., Galle S., Lebel T.
Environmental Research Letters, (August 2019).
Small scale eco-hydrological regime shifts and impacts on regional changes in the Sahel.
Wendling V., Peugeot C., Garcia-Mayor A., Hiernaux P., Mougin E., Walcker R., Grippa M., Kergoat L., Lebel T.
EGU General Assembly 2019, Wien 7-12 April 2019, session Climate tipping points, critical thresholds and ecosystem resilience.
Tipping points and regime shifts in dynamic systems : a new modeling approach to study Sahelian ecohydrology
Wendling V., Peugeot C., Garcia-Mayor A., Hiernaux P. Mougin E., Grippa M., Kergoat L., Lebel T.
AMMA-CATCH International conference. « Observatories of the Critical Zone in Africa: current issues and findings », Niamey, Niger, 12-14 November 2018