Detecting Decadal Temporal Shifts in Rainfall Across the West African Sahel During the Twentieth Century

Rainfall in the West African Sahel has substantial spatial intra-/inter-annual variability. This study analyzed rainfall trends for onset (ON) and cessation (CS) across selected locations in the West African Sahel during the twentieth century. These locations are Badalabougou and Boumboum in Mali; Achouaden and Abadam in Niger; Abadji and Chandjone in Chad; Los and Bakao in Senegal. ON was defined in this study as the time when daily precipitation is consistently greater than the local annual daily average. At the same time, CS occurs when precipitation systematically drops below that value. This study investigates the decadal trends of ON and CS using Mann–Kendall and Sen Slope analysis in the study area. Daily rainfall data was obtained from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) at a 0.5° × 0.5° grid resolution for 1901–2000. Results showed that OS of rainfall at Achouadene had a significant trend of –2.1, – 2.9 and 6.2 days during the 1921–1930, 1970–1980 and 1991–2000 periods, respectively. This location was prone to pronounce significant changes in onset days among the selected locations. During the 1970–1980 period, Abadam, Achouaden and Abadji exhibited significant decreasing trends of – 4.2, – 2.9 and – 3.0 days, respectively. Badalabougou and Chandjone experienced a significant decreasing trend of − 2.1 and − 2.9 days during the 1921–1930 decade. Results showed an overall decreasing trend in the ON, while only a few locations exhibited significant trends in CS of rainfall. The study has presented an overview of the decadal trends in ON and CS in a representative climate hotspot area of the West African Sahel.