Critical Hydroclimatic Transitions in Afrotropical Ecosystems

Afrotropical ecosystems span a broad water availability gradient—from grasslands and savannas to rainforests—but even rainforests are comparatively drier than those of the Amazon or Southeast Asia. Hence water availability determines to a large extent the spatial distribution of Afrotropical ecosystems. Here we show that future greenhouse gas emissions will induce diverging trends in both total precipitation and its seasonal variability across tropical Africa’s biomes, using remotely sensed land cover types, observational datasets of historical hydroclimate and Earth system model projections. Seasonally dry forests are projected to face increasing drought stress, while non-forest vegetation will become mostly wetter. The maximum climatological water deficit of carbon-dense rainforests in the Afrotropics is expected to increase in the Northern Hemisphere and decrease in the Southern Hemisphere. Although biome transitions and net changes in carbon stocks remain limited, regional discrepancies emerge, with potential woody encroachments in grasslands offsetting rainforest declines. Our results show that, even without widespread biome collapse, emerging hydroclimatic regime shifts will reorganize where Afrotropical ecosystems can establish, with far-reaching consequences for biodiversity, the land carbon sink, and climate adaptation across tropical Africa.