We estimate the production function for agricultural output in Eastern Africa incorporating climate variables disaggregated into growing and non-growing seasons. We find a substantial negative effect of within growing season variance of precipitation. We simulate predicted climate change for the region and find a resulting output reduction of between 1.2% and 4.5%. Our simulation also demonstrates substantial potential for economic benefits from mitigating the effects of within growing season precipitation variability through conventional technologies such as flexible planting and rainwater harvesting on the same scale as the potential loss from predicted climate change.