Abstract: Climate risk threatens Sub-Saharan Africa's rain-fed agriculture. Using micro-data from six countries, I show that a one-week delay in the onset of the rainy season reduces yields by 2% and consumption by 1%. Damages disproportionately harm the most vulnerable, with the effects being most pronounced on female-managed plots, while education and wealth build resilience. Farmers adapt by delaying planting, but this is insufficient due to informational frictions. False onsets—misleading early rains followed by a dry spell—trigger premature planting, increasing damages. The negative impacts are concentrated in locations experiencing long-term climatic shifts, indicating a persistent failure to adapt. Projecting these damages forward reveals a substantial threat: cumulative discounted losses from 2025 to 2050 could reach up to 10% of 2024 real GDP. These findings establish shifts in seasonal timing as a first-order economic threat and highlight the value of short-range forecasts in mitigating this risk.

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