Tanzania Journal of Agricultural Sciences 2015, 14(1) : 34-42Rainfed maize (Zea mays) in semi-arid Sub-Saharan Africa is subject to many climate-related risks—including agricultural dry spells and droughts. Effectively selecting appropriate agricultural water management strategies must first begin with evaluation of the potential climate-related risks. This article evaluates dry spell occurrence in the Mabogini Village—located within a semiarid area in Tanzania—using a water balance approach with nineteen years of historical daily precipitation data. The water balance equation was related to crop water requirements to evaluate both the prevalence of agricultural dry spells as well as estimate the water deficits throughout the same time period. Only four of the nineteen seasons did not experience a dry spell of at least five consecutive days. 37% of the seasons had at least one dry spell of 6-10 days while 63% had at least one dry spell of greater than 15 days. Soil water deficit in relation to crop production ranged from 0-140 mm. This study concludes that dry spells lasting greater than 15 days throughout 63% of the past 19 growing seasons represent a high risk to smallholder farmers in the area. The high prevalence of long dry spells suggests that rainfed maize production is not sustainable in the region without interventions. However, relatively small water deficits suggest that proper water capture, storage, and supplemental irrigation methods could help to bridge the gap between dry spells. It is therefore recommended that water management practices be put in place immediately to support productive and sustainable maize production in the area.