Chapter 13
Assessment of Hydrological Impacts
of Climate Change on the Diarha
Watershed
Ibrahima Thiaw, Bakary Faty, Honoré Dacosta, Anastasie Mendy,
Abel Vincent Manga, and Amadou Abdoul Sow
Abstract This article assesses the impacts of climate change on surface water
resources in the Diarha watershed, a tributary of the Gambia River, in West Africa.
The analysis is based on the parallel application of two hydrological models (GR4J
and SAC-SMA) with RS Minerve software and includes an automatic optimization
based on a multi-criteria function that aggregates the Nash, Nash-ln, KGE’ and R
criteria according to the Shuffled Complex Evolution-University of Arizona (SCEUA) method. The hydrological model that best replicates the rainfall-runoff relationship during the cross-validation phase (1975–1992 and 1998–2003) was fed with
daily climate data projected for the 2050 horizon, while evaluation of future impacts
of climate change on basin hydrology was based on the use of three Regional Climate
Models (IPSL-CM5A-LR, INM-CM4, and GFDL-ESM2G) from CORDEX climate
projections. CDF-t bias correction was applied to these scenarios before application
to the hydrological model. Flow rates of the Diarha river basin were subsequently
calculated in order to characterize their contribution to the projected climate scenarios
at the 2050 horizon. Results indicate that the GR4J model is better able to reproduce the observed hydrographs of the Diarha river basin than the SAC-SMA model:
values of the Nash-ln, KGE’ and R criteria were greater than 80% in both calibration
and validation, while the Nash model’s performance varied between 91% (in calibration) and 62% (in validation). The models predict that climate change will have a
significant impact on the Diarha’s future flows, characterized by a decrease in annual
streamflows of 5% under the RCP4.5 scenario and 25% under RCP8.5. The models
furthermore project a decrease in the characteristic high flows (DMAX, DCC_10j,
DCC_20j, DC1, DC2 and DC3) in both emission scenarios.
Keywords Climate change · CORDEX · Diarha watershed · Hydrological
impacts · RS minerve
I. Thiaw (B) · B. Faty · H. Dacosta · A. Mendy · A. V. Manga · A. A. Sow
Laboratory of Morphology and Hydrology, Cheikh Anta Diop University, P.O.B 5005, Dakar,
Senegal
e-mail: ibrahima4.thiaw@ucad.edu.sn
© Springer Nature Switzerland AG 2021
S. Diop et al. (eds.), Climate Change and Water Resources in Africa,
https://doi.org/10.1007/978-3-030-61225-2_13
277
Assessment of Hydrological Impacts
of Climate Change on the Diarha
Watershed
Ibrahima Thiaw, Bakary Faty, Honoré Dacosta, Anastasie Mendy,
Abel Vincent Manga, and Amadou Abdoul Sow
Abstract This article assesses the impacts of climate change on surface water
resources in the Diarha watershed, a tributary of the Gambia River, in West Africa.
The analysis is based on the parallel application of two hydrological models (GR4J
and SAC-SMA) with RS Minerve software and includes an automatic optimization
based on a multi-criteria function that aggregates the Nash, Nash-ln, KGE’ and R
criteria according to the Shuffled Complex Evolution-University of Arizona (SCEUA) method. The hydrological model that best replicates the rainfall-runoff relationship during the cross-validation phase (1975–1992 and 1998–2003) was fed with
daily climate data projected for the 2050 horizon, while evaluation of future impacts
of climate change on basin hydrology was based on the use of three Regional Climate
Models (IPSL-CM5A-LR, INM-CM4, and GFDL-ESM2G) from CORDEX climate
projections. CDF-t bias correction was applied to these scenarios before application
to the hydrological model. Flow rates of the Diarha river basin were subsequently
calculated in order to characterize their contribution to the projected climate scenarios
at the 2050 horizon. Results indicate that the GR4J model is better able to reproduce the observed hydrographs of the Diarha river basin than the SAC-SMA model:
values of the Nash-ln, KGE’ and R criteria were greater than 80% in both calibration
and validation, while the Nash model’s performance varied between 91% (in calibration) and 62% (in validation). The models predict that climate change will have a
significant impact on the Diarha’s future flows, characterized by a decrease in annual
streamflows of 5% under the RCP4.5 scenario and 25% under RCP8.5. The models
furthermore project a decrease in the characteristic high flows (DMAX, DCC_10j,
DCC_20j, DC1, DC2 and DC3) in both emission scenarios.
Keywords Climate change · CORDEX · Diarha watershed · Hydrological
impacts · RS minerve
I. Thiaw (B) · B. Faty · H. Dacosta · A. Mendy · A. V. Manga · A. A. Sow
Laboratory of Morphology and Hydrology, Cheikh Anta Diop University, P.O.B 5005, Dakar,
Senegal
e-mail: ibrahima4.thiaw@ucad.edu.sn
© Springer Nature Switzerland AG 2021
S. Diop et al. (eds.), Climate Change and Water Resources in Africa,
https://doi.org/10.1007/978-3-030-61225-2_13
277