Sub-Saharan Africa (SSA) is far from becoming self-sufficiency in cereal production. The recurrence of droughts in the past decades has exacerbated the situation. Understanding the spatial and temporal dynamics of crop drought vulnerability during phenological development of crops is important to identify relief policy and amicable solutions to drought. However, most studies lack understanding from such multiple perspectives. Here, we quantify the vulnerability of maize, millet, and sorghum to drought during different crop growth using a fuzzy rule-based method. Apart from providing spatial and temporal details, we provide complementary information on various stresses, which trigger vulnerability. The analytical technique integrated with a large geographical scale crop modeling offers the opportunity for drought risk studies over the whole of SSA.