Spatio-temporal analysis of rainfall variability and seasonality in Malawi

Food security in Malawi relies on rainfall amount and timing. Because agricultural production is the main source of income for most rural communities, increased frequency of extreme events will increase the risk of production failure-a major threat to food security. Evidence of changing rainfall is reported by farmers and by recent analysis of gauge measurements, but these studies are limited due to small sample size, type of tests, or both. The main goal of this study is to test both statistically significant and robust but less significant changes in rainfall and rainy season for 1981-2018 using a high-resolution gridded dataset (0.05 degrees). We analyzed different indices including onset, length, and cessation of rainy season, number of dry days, and number of extreme events during the rainy season. Our results show that roughly one-third of Malawi has experienced at least one type of significant change in rainfall indices during the study period. For instance, Northern Malawi had similar to 2 fewer extreme event days/decade and an end of season similar to 5 days/decade earlier as well as similar to 5 fewer dry days/decade. For the entire time period, delayed onset varies spatially from 18 to 35 days, number of dry days has decreased 21.6 days, the rainy season has ended 28.8 days earlier in the north and 36 days earlier in the south, and the number of extreme events has decreased 5 to 7 days in many places. The results are heterogeneous spatially and suggest that broad scale forcings are not driving them.