Long term spatial trends in West African monsoon precipitation

Across West Africa, rainfall is a vital weather component. Its importance in agriculture, the economy, and even governance across the region cannot be overstated due to the nature of the socio-economic vulnerabilities within this region. Therefore, the performance of the region’s economy and its governance depend largely on rainfall distribution directly or indirectly. This study aims to analyze rainfall distribution across the West African region using four indices: the mean rainfall distribution per month, days with rainfall exceeding a 1 mm threshold, days with rainfall exceeding a 5 mm threshold, and the maximum amount of rainfall each year. The CPC Global Unified Gauge-Based Analysis of Daily Precipitation with a resolution of From 1979 to 2020 was used in this study. Trend was determined using the non-parametric Sen’s slope and Mann-Kendall tests. The number of days with rainfall greater than 1 mm and 5 mm showed positive trends between 0 and 0.4 mm/month during the considered months, although the trends were not statistically significant. Locations off the coast of Sierra Leone and Liberia, as well as on the continent of Nigeria, showed statistically significant negative trends. Considering the number of days with heavy rainfall from April to July, we observed a reduced trend in values compared to days with normal precipitation. This implies that although normal rainfall will increase, it will not be as much as heavy rainfall.