When Good Soil Turns Bad: Evidence of Non-Monotonic Drought Vulnerability in African Croplands

Soils with high water holding capacity are widely expected to buffer crops against drought.Using satellite vegetation indices, precipitation data, and soil maps across approximately 40,000 grid cells in Sub-Saharan Africa from 2017 to 2022, we document a contrary pattern: regions with higher clay content experience larger declines in vegetation health during moderate droughts.This relationship reverses only under extreme drought conditions, which occur in about 4% of observations.At moderate drought, a one-unit increase in drought intensity reduces vegetation health by 5.9% in low-clay soils but by 8.7% in highclay soils.The finding is robust across alternative vegetation indices, climate zones, and model specifications.Our analysis is correlational and does not identify causal mechanisms, but the pattern is consistent with several explanations including risk compensation, crop composition differences, and nonlinear soil-water dynamics.These results suggest that favorable soil conditions do not necessarily confer drought resilience, with implications for agricultural vulnerability assessment under climate change.