This study analyzes the hydroclimatic variability of the watershed south of the Saloum River over the period 1961–2023 using the Standardized Precipitation Index (IPS) and the Standardized Precipitation and Evapotranspiration Index (IPES), combined with statistical tests and seasonal methods (aridity indices of De Martonne, Bagnouls-Gaussen, and Euverte). The results confirm a Sudano-Sahelian climate characterized by a long dry season and a concentration of rains between June and October. Three climatic phases are identified: a humid phase, a dominant dry phase between the 1970s and 1990s, and a partial and irregular recovery since the 2000s. A Marked spatial variability is observed, with a more contrasted dynamic at Kaolack, more stable at Fatick, and a recent moist trend at Nioro. However, the irregularity of rainfall does not confirm of a sustainable return to normal, a situation also observed in other West African regions. The IPS proves to be more sensitive to rainfall extremes, while the IPES integrates the effect of increased temperatures via potential evapotranspiration. In this context of climate change, the IPES seems more suitable than the IPS for the analysis of drought and humidity trends at the territorial level and for support to water resources management.

With no surface water available during the dry season in Touba, using groundwater for irrigation is a real alternative. In general, the poor quality of irrigation water has an effect on soil quality, which is harmful to plant growth and therefore has an impact on yield. Irrigation water can even pose a risk to human health. It is crucial to assess the quality of irrigation water before use. Consequently, the aim of this study is to assess the suitability of the groundwater in TOUBA and the surrounding area for irrigation. For the purposes of this study, the Sodium Absorption Ratio (SAR), the Magnesium Absorption Ratio (MAR), the Doneen Permeability Index (IP) and the Potential Salinity (SP) were calculated for sixteen (16) boreholes tapping the Maastrichtian aquifer. The determination of these parameters is based on hydro-chemical data (Electrical Conductivity (EC), concentration of chloride (Cl-), sulphate (SO4 2-), calcium (Ca 2+), bicarbonate (H03-), magnesium (Mg 2+), sodium (Na +) and potassium (K+) ions) received from the Water Resources Management and Planning Department (DGPRE) and the Rural Drilling Office (OFOR). According to the SAR, 12.5% are C3S1, 12.5% C1S4, 31.25% C4S3-C3S4, 6.25% C2S4 and 37.5% C4S4. 93.75% of the samples have a MAR above 60% [FAO limit]. Determination of the Doneen index (PI) shows that all the samples have PI above 75%. However, only 18.75% of the waters studied have the SP values recommended by Doneen.