Effect of rainfall variability on the length of the crop growing period over the past three decades in central Malawi

The present study investigates the trends of onset, cessation and length of growing period in central Malawi, critical for crop management decisions. These factors are especially important for the smallholder agricultural systems that predominantly depend on rainfall as in most parts of semi-arid southern African countries, such as the central region of Malawi. Onset identification was based on rainfall accumulation, while cessation was based on daily analysis of the ratio of actual to reference crop evapotranspiration. The length of the growing period for a particular season was obtained from the difference between the onset and cessation of that particular season. Series of 30 yr of historical daily climatic data (1980 to 2009) from 5 meteorological stations within the central region of Malawi were considered. Results indicated changes in the onset, cessation and consequently length of the growing period over the past 3 decades. A delayed onset and early cessation of the growing period, resulting in a shorter growing period, were observed. Seasonal rainfall amounts have changed little, but the number of rainfall events has changed remarkably. January has become wetter recently, including higher rainfall amounts and higher rainfall intensity. The results suggest the need for designing appropriate agronomic, soil and water management strategies to offset the negative effects of rainfall variability, especially for smallholder rainfed agriculture.