Dry spell analysis and maize yields for two semi-arid locations in East Africa

High variability in rainfall occurrence and amounts together with high evaporative demand create severe constraints for crop growth and yields in dry sub-humid and semi-arid farming areas in east Africa. Meteorological analyses on rainfall distribution are common, but generally focus on assessing drought occurrence on annual and seasonal basis. This paper presents two types of seasonal dry spell analysis, using easy accessible data on daily rainfall and evapotranspiration for two semi-arid locations in east Africa for 20-23 years. The meteorological dry spell analysis was obtained by Markov chain process, and the agricultural dry spell analysis used rainfall data in a simple water balance model also describing impact on maize (Zea mays L.) growth due to water availability on clay or sandy soil. The meteorological dry spell analysis showed a minimum probability of 20% of dry spells exceeding 10 days at both sites, increasing to 70% or more depending on onset of season, during approximate flowering and early grain filling stage. The agricultural dry spell analysis showed that maize was exposed to at least one dry spell of 10 days or longer in 74-80% of seasons at both sites. Maize on sandy soil experienced dry spells exceeding 10 days, three-four times more often than maize on clay soil during flowering and grain filling stages. In addition, the water balance analysis indicated substantial water losses by surface runoff and deep percolation as the crop utilised only 36-64% on average of seasonal rainfall. Such large proportion of non-productive water flow in the field water balance may provide scope for dry spell mitigation through improved water management strategies.