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Hydrological regime shifts in Sahelian watersheds: an investigation with a simple dynamical model driven by annual precipitation.

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Title: Hydrological regime shifts in Sahelian watersheds: an investigation with a simple dynamical model driven by annual precipitation.
Authors: Le Roux, Erwan1 (AUTHOR), Wendling, Valentin2 (AUTHOR), Panthou, Gérémy3 (AUTHOR), Dubas, Océane3 (AUTHOR), Vandervaere, Jean-Pierre3 (AUTHOR), Hector, Basile3 (AUTHOR), Favreau, Guillaume3 (AUTHOR), Cohard, Jean-Martial3 (AUTHOR), Pierre, Caroline4 (AUTHOR), Descroix, Luc5 (AUTHOR), Mougin, Eric6 (AUTHOR), Grippa, Manuela6 (AUTHOR), Kergoat, Laurent6 (AUTHOR), Demarty, Jérôme7 (AUTHOR), Rouche, Nathalie7 (AUTHOR), Etchanchu, Jordi7 (AUTHOR), Peugeot, Christophe7 (AUTHOR) christophe.peugeot@ird.fr
Source: Hydrology & Earth System Sciences. 2026, Vol. 30 Issue 4, p929-944. 16p.
Subject Terms: *Meteorological precipitation, *Runoff analysis, *Watershed management, *Hydrologic cycle, *Watersheds, *Ecological resilience, *Dynamic models, *Droughts
Geographic Terms: Sub-Saharan Africa, Sahel
Abstract: The Sahel, the semi-arid fringe south of the Sahara, experienced severe meteorological droughts in the 1970s–1980s. During and after these droughts, watersheds in the Central Sahel have experienced an increase in the annual runoff coefficient (annual runoff normalized by annual precipitation). We hypothesize that these increases correspond to regime shifts. To investigate the timing of these regime shifts, we introduce a lumped model that represents feedbacks between soil, water and vegetation at the watershed scale and the annual time step. This model relies on runoff coefficient as a constraint for the state variable and precipitation as unique external forcing. Four watersheds (Gorouol, Dargol, Nakanbé and Sirba), with pluri-decennial observations (1950s–2010s), are modeled. For each watershed, one million parameterizations of this model are sampled and run, and an ensemble of one thousand best parameterizations is selected based on observed runoff coefficients. Our results show that this model can reproduce the trend of runoff coefficients. For all watersheds, almost all selected parameterizations from the ensemble are bistable. We define two alternative runoff coefficient regimes (a low and a high regime) by splitting with a threshold the bifurcation diagram of bistable parameterizations. Most selected parameterizations undergo regime shifts: simulated runoff coefficients belong to the low regime in 1965 and to the high regime in 2014. Finally, we find that the year of the regime shift, defined as the year when the number of regime shifts is maximized, was 1971, 1972, 1973, 1983 for the Gorouol, Nakanbé, Dargol and Sirba watershed, respectively. These results were obtained with a parsimonious model which deliberately neglects fine-scale processes of Sahelian hydrology. It would therefore be wise to supplement this analysis with other models – with varying levels of complexity – that also allow regime shifting. Overall, this article proposes simple ideas toward improving the modelling and characterization of hydrological regime shifts. [ABSTRACT FROM AUTHOR]
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  Label: Title
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  Data: Hydrological regime shifts in Sahelian watersheds: an investigation with a simple dynamical model driven by annual precipitation.
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  Data: <searchLink fieldCode="AR" term="%22Le Roux%2C+Erwan%22">Le Roux, Erwan</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Wendling%2C+Valentin%22">Wendling, Valentin</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Panthou%2C+Gérémy%22">Panthou, Gérémy</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Dubas%2C+Océane%22">Dubas, Océane</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Vandervaere%2C+Jean-Pierre%22">Vandervaere, Jean-Pierre</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Hector%2C+Basile%22">Hector, Basile</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Favreau%2C+Guillaume%22">Favreau, Guillaume</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Cohard%2C+Jean-Martial%22">Cohard, Jean-Martial</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Pierre%2C+Caroline%22">Pierre, Caroline</searchLink><relatesTo>4</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Descroix%2C+Luc%22">Descroix, Luc</searchLink><relatesTo>5</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Mougin%2C+Eric%22">Mougin, Eric</searchLink><relatesTo>6</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Grippa%2C+Manuela%22">Grippa, Manuela</searchLink><relatesTo>6</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Kergoat%2C+Laurent%22">Kergoat, Laurent</searchLink><relatesTo>6</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Demarty%2C+Jérôme%22">Demarty, Jérôme</searchLink><relatesTo>7</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Rouche%2C+Nathalie%22">Rouche, Nathalie</searchLink><relatesTo>7</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Etchanchu%2C+Jordi%22">Etchanchu, Jordi</searchLink><relatesTo>7</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Peugeot%2C+Christophe%22">Peugeot, Christophe</searchLink><relatesTo>7</relatesTo> (AUTHOR)<i> christophe.peugeot@ird.fr</i>
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  Data: <searchLink fieldCode="JN" term="%22Hydrology+%26+Earth+System+Sciences%22">Hydrology & Earth System Sciences</searchLink>. 2026, Vol. 30 Issue 4, p929-944. 16p.
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  Label: Subject Terms
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  Data: *<searchLink fieldCode="DE" term="%22Meteorological+precipitation%22">Meteorological precipitation</searchLink><br />*<searchLink fieldCode="DE" term="%22Runoff+analysis%22">Runoff analysis</searchLink><br />*<searchLink fieldCode="DE" term="%22Watershed+management%22">Watershed management</searchLink><br />*<searchLink fieldCode="DE" term="%22Hydrologic+cycle%22">Hydrologic cycle</searchLink><br />*<searchLink fieldCode="DE" term="%22Watersheds%22">Watersheds</searchLink><br />*<searchLink fieldCode="DE" term="%22Ecological+resilience%22">Ecological resilience</searchLink><br />*<searchLink fieldCode="DE" term="%22Dynamic+models%22">Dynamic models</searchLink><br />*<searchLink fieldCode="DE" term="%22Droughts%22">Droughts</searchLink>
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  Label: Geographic Terms
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  Data: <searchLink fieldCode="DE" term="%22Sub-Saharan+Africa%22">Sub-Saharan Africa</searchLink><br /><searchLink fieldCode="DE" term="%22Sahel%22">Sahel</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: The Sahel, the semi-arid fringe south of the Sahara, experienced severe meteorological droughts in the 1970s–1980s. During and after these droughts, watersheds in the Central Sahel have experienced an increase in the annual runoff coefficient (annual runoff normalized by annual precipitation). We hypothesize that these increases correspond to regime shifts. To investigate the timing of these regime shifts, we introduce a lumped model that represents feedbacks between soil, water and vegetation at the watershed scale and the annual time step. This model relies on runoff coefficient as a constraint for the state variable and precipitation as unique external forcing. Four watersheds (Gorouol, Dargol, Nakanbé and Sirba), with pluri-decennial observations (1950s–2010s), are modeled. For each watershed, one million parameterizations of this model are sampled and run, and an ensemble of one thousand best parameterizations is selected based on observed runoff coefficients. Our results show that this model can reproduce the trend of runoff coefficients. For all watersheds, almost all selected parameterizations from the ensemble are bistable. We define two alternative runoff coefficient regimes (a low and a high regime) by splitting with a threshold the bifurcation diagram of bistable parameterizations. Most selected parameterizations undergo regime shifts: simulated runoff coefficients belong to the low regime in 1965 and to the high regime in 2014. Finally, we find that the year of the regime shift, defined as the year when the number of regime shifts is maximized, was 1971, 1972, 1973, 1983 for the Gorouol, Nakanbé, Dargol and Sirba watershed, respectively. These results were obtained with a parsimonious model which deliberately neglects fine-scale processes of Sahelian hydrology. It would therefore be wise to supplement this analysis with other models – with varying levels of complexity – that also allow regime shifting. Overall, this article proposes simple ideas toward improving the modelling and characterization of hydrological regime shifts. [ABSTRACT FROM AUTHOR]
PLink https://search.ebscohost.com/login.aspx?direct=true&site=eds-live&db=enr&AN=192129855
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      – Type: doi
        Value: 10.5194/hess-30-929-2026
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      – Code: eng
        Text: English
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        PageCount: 16
        StartPage: 929
    Subjects:
      – SubjectFull: Meteorological precipitation
        Type: general
      – SubjectFull: Runoff analysis
        Type: general
      – SubjectFull: Watershed management
        Type: general
      – SubjectFull: Hydrologic cycle
        Type: general
      – SubjectFull: Watersheds
        Type: general
      – SubjectFull: Ecological resilience
        Type: general
      – SubjectFull: Dynamic models
        Type: general
      – SubjectFull: Droughts
        Type: general
      – SubjectFull: Sub-Saharan Africa
        Type: general
      – SubjectFull: Sahel
        Type: general
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      – TitleFull: Hydrological regime shifts in Sahelian watersheds: an investigation with a simple dynamical model driven by annual precipitation.
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