Impacts of Climate and Environmental Changes on Water Resources: A Multi-Scale Study Based on Nakanbé Nested Watersheds in West African Sahel

Study region: Nakanbe River watershed in the West Africa Sahel (WAS). Study focus: This study aims to better understand the hydrological behavior of WAS watersheds, which experienced Sahelian hydrological paradoxes (SHP). Budyko framework was employed to evaluate the impact of climate change, environmental change and climate-environment interaction on surface runoff change in seven nested watersheds (38 - 21,178 km(2)) over the period 1965-2018. New hydrological insights for the region: Based on time-series stationarity statistical tests, the study period was divided into one baseline period (1965-1977) and three impacted periods (1978 1994, 1995 2006 and 2007 2018). Compared to the baseline period, the period 1978 1994 was characterized by a decrease in precipitation and an increase in runoff (first SHP). During the period 1995-2018, the runoff coefficient, which increased despite the observed regreening, was interpreted as evidence of the second SHP. The impact study showed that environmental change was the main driver of the first SHP (contribution reached +175 %), then climate-environment interaction became increasingly dominant during the second SHP (contribution reaching +68 %). The watersheds evolution in Budyko framework showed that the Fu Budyko-type model parameter appears to be a good indicator of soil water holding capacity spatio-temporal variability. Our results highlight the consequences of climate and environmental changes on surface runoff in the Sahelian context and might help in developing informed land management and restoration strategies to control runoff coefficients.