Hydroclimatic Impacts of Volcanic Eruptions across Africa: An Aridity Index Perspective

Volcanic eruptions are an important driver of hydroclimate variability over Africa, yet their continent-wide impacts on aridity have not been systematically quantified. Using simulations of the Community Earth System Model Last Millennium Ensemble (CESM-LME), this study investigates the impacts of volcanic eruptions on the African aridity based on an aridity index (AI), defined as the ratio of precipitation to potential evapotranspiration (PET). Results reveal that aridity responses depend on both the season and the volcanic eruption latitude. Drying tends to occur within the climatological rainy-season band, and its position is further modulated by eruption latitude: Northern Hemisphere eruptions shift the main drying zone northward, whereas Southern Hemisphere eruptions shift it southward. Across all eruption events, soil moisture and surface runoff anomalies broadly agree with AI changes. The decomposition of AI anomalies reveals that precipitation reduction, which primarily results from circulation-driven reductions in horizontal and vertical moisture advection, dominates the drying, whereas PET plays a secondary role. These results provide a physical basis for improving predictions of African aridity following volcanic eruptions.