Seasonal precipitation changes in response to long-term aerosol anomalies: A case from West Africa

Abstract

In southern West Africa (SWA), highly absorbing aerosol types can significantly alter precipitation trends. Therefore, it is essential to investigate the changes in precipitation anomalies from the dry season to the monsoon season. This study examines the impact of aerosol anomalies on precipitation trends and anomalies during the pre-monsoon season in the SWA region. The study analyzed monthly datasets of aerosol optical depth (AOD_550nm), precipitation, and atmospheric parameters from 1981 to 2020. The results base on anomaly and MK trend tests shows a decline in precipitation trends and anomalies across most of SWA during the last two decades (2001–2020). High positive spatial AOD anomalies corresponded with negative precipitation anomaly patterns. The regression analysis indicates a strong negative spatial correlation and slope between AOD and precipitation, especially along the coasts, with statistical significance for both periods. However, precipitation did not show a statistically significant relationship with zonal wind speed, geopotential height, or relative humidity at 850 hPa, even though these parameters exhibited stronger negative correlations and slope patterns over major cities in coastal SWA during the last two decades. The decrease in pre-monsoon precipitation anomalies suggests the dominance of aerosol-saturated atmosphere, which could diminish the influence of atmospheric parameters on cloud microphysics and precipitation, likely exacerbated by proximity to the ocean. The findings highlight the possible impact on the region's hydrological system due to amplification in aerosol concentrations; therefore, policies on emission control and mitigation are encouraged.