EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Tipping points in hydrology: observed regional regime shift and System Dynamics modeling

Valentin Wendling1, Christophe Peugeot1, Manuela Grippa2, Laurent Kergoat2, Eric Mougin2, Pierre Hiernaux2, Nathalie Rouché1, Geremy Panthou3, Jean-Louis Rajot4, Caroline Pierre4, Olivier Mora5, Angeles Garcia-Mayor6, Abdramane Ba7, Emmanuel Lawin8, Ibrahim Bouzou-Moussa9, Jerôme Demarty1, Jordi Etchanchu1, Basile Hector3, Sylvie Galle3, Thierry Lebel3, and the TipHyc Project*
Valentin Wendling et al.
  • 1Hydrosciences Montpellier (IRD, Univ. Montpellier, CNRS) Montpellier, France
  • 2Géosciences Environnement Toulouse (CNRS, IRD, UPS) Toulouse, France
  • 3Institut des Géosciences de L’environnement (Univ. Grenoble Alpes, IRD, CNRS, Grenoble INP), Grenoble, France
  • 4Institut d’Ecologie et des Sciences de l’Environnement de Paris (CNRS, Sorbonne Univ., Univ Paris Est Creteil, IRD, INRAE, Univ. de Paris) Paris, France
  • 5Délégation à l'Expertise scientifique collective, à la Prospective et aux Etudes (INRAE), Paris France
  • 6Utrecht University, Utrecht, The Netherlands
  • 7Institut National de L’Eau, Cotonou, Benin
  • 8Université Abdou-Moumouni, Niamey, Niger
  • 9Université des sciences, des techniques et des technologies de Bamako, Bamako, Mali
  • *A full list of authors appears at the end of the abstract

River runoff and climate data existing from 1950 to present time in West Africa are analyzed over a climatic gradient from the Sahel (semi-arid) to the Gulf of Guinea (humid). The region experienced a severe drought in the 70s-90s, with strong impact on the vegetation, soils and populations. We show that the hydrological regime in the Sahel has shifted: the runoff increased significantly between pre- and post-drought periods and is still increasing. In the Guinean region, instead, no shift is observed.

This suggests that a tipping point could have been passed, triggered by climate and/or land use change. In order to explore this hypothesis, we developed a System Dynamics model representing feedbacks between soil, vegetation and flow connectivity of hillslopes, channels and aquifers. Model runs were initialized in 1950 with maps of land use/land cover, and fed with observed rainfall (climate external forcing).

The modeling results accurately represent the observed evolution of the hydrological regime on the watersheds monitored since the 50s (ranging from 1 to 50000 km²). The model revealed that alternative stable states can exist for the climatic conditions of the study period. From the model runs, we showed that the drought triggered the crossing of a tipping point (rainfall threshold), which explains the regime shift. We identified domains within the watersheds where tipping occurred at small scale, leading to larger scale shifts. This result supports that tipping points exist in semi-arid systems where ecohydrology plays a major role. This approach seems well suited to identify areas of high risk of irreversible hydrological regime shifts under different climate and land-use scenarios.

TipHyc Project:

H. Alassane, A. Ba, J-F. Badou, M. Boucher, I. Bouzou-Moussa, J-M. Cohard, S. Conrad, M. de Fleury, J. Demarty, L. Descroix, O. Diancoumba, F. Djigbo, J. Etchanchu, B. Fatogomoa, G. Favreau, S. Galle, F. Gangneron, E. Guilman, B. Hector, P. Hiernaux, J. Hounkpé, R. Houngue, B.A. Issoufou, L. Kergoat, V. Kotchoni, E. Lawin, T. Lebel, M. Malam-Abdou, O. Mamadou, A. G. Mayor, O. Mora, E. Mougin, M’P. N'Tcha, Y. Nazoumou, M. Oï, G. Panthou, C. Pierre, C. Peugeot, G. Quantin, J-L. Rajot, N. Rouché, S. Sanogo, M. Sounmaïla, K. Sy, A. Touré, J-P. Vandervaere, T. Vischel, V. Wendling.

How to cite: 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., Demarty, J., Etchanchu, J., Hector, B., Galle, S., and Lebel, T. and the TipHyc Project: Tipping points in hydrology: observed regional regime shift and System Dynamics modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5433,, 2022.