Spatial and Temporal Variability of Rainfall in South-central Senegal: Example of the Fatick and Kaolack Regions

One of the manifestations of climate change in the Sahel is a decrease in rainfall, which has led to a sharp decline in water potential in the south-central Senegal. The objective of this study is to understand the changes in rainfall through time and space, in the south-central Senegal (Fatick and Kaolack regions), to better plan water management for sustainable development. The rainfall data used ranges from 1961 to 2020 for the sites of Gossas, Foundiougne, Guinguineo and Nioro, and from 1951 to 2020 for the sites of Fatick and Kaolack. Pettitt and Buishand break tests were used to detect changes in rainfall patterns, Hubert segmentation was used to highlight sub-periods within the time series, and Standardized Precipitation Indices (SPI) were used to highlight deficits and surpluses. The results of break tests and Hubert segmentation show a decrease in average rainfall between the 1960s and 1970s, and an increase between the 1990s and 2000s, for some of the sites. The decrease in the 1960s and 1970s was early in sites in the Fatick region (Gossas, Fatick and Foundiougne) and late or absent in the Kaolack region (Guinguineo, Kaolack and Nioro). As for the increase in the 1990s and 2000s, it was first observed in the south and center of the study area in the 1990s (Nioro and Kaolack). In the 2000s, the increase was observed further north (Fatick and Gossas). The Standardized Precipitation Index shows reduced rainfall for 1971-2000 compared to the surrounding periods. Coefficient of variation values show that dispersion is lowest in the wetter years 1950 for two sites (Fatick and Kaolack), 1990 and 2000 for four sites (Gossas, Foundiougne, Guinguineo and Nioro). The highest coefficients of variation were detected in the drought years 1960, 1970 and 1980 for these four sites (Gossas, Foundiougne, Guinguineo and Nioro). This is not the case at the Fatick site, where the coefficients of variation for the 1970s, 1980s and 1990s are higher than those for 2000 and 2010. Coefficients of variation increase in the 2010s at five sites (Kaolack, Gossas, Foundiougne, Guinguineo and Nioro). The highest coefficients of variation were recorded in 2010 in Gossas, Guinguineo and Nioro. The decrease in average rainfall from the 1960s to the 1990s, and the increase in the 1990s and 2000s detected in most of the study sites, corroborates results of other studies from West and Central Africa.