ENSO and interannual rainfall variability in Uganda: implications for agricultural management

The El Nino–Southern Oscillation (ENSO) is correlated with the short rainy season (September–December) in East Africa. Seasonal climate forecasts made on this basis are being disseminated in the hope that this information will be useful in regional or even local planning and resource management. In order to improve the likelihood of success in using regional forecasts in Uganda, particularly in the agricultural sector, climate analysis was performed at the sub-regional level with distinctions being made between unimodal (short season peak in August) and bimodal (short season peak in November) rainfall zones. Monthly climate data from 1931 to 1960 were available for 33 sites. Averaging across all stations, it is shown that Pacific Ocean NINO3 region sea-surface temperatures (SSTs) from July to September (JAS) are significantly correlated with both the concurrent August–September (AS) rainfall (r=−0.75) and the following November–December (ND) rainfall (r=0.57), but with opposite signs. When station data are separated into uni- and bimodal sites, it becomes clear that the importance of ENSO events is different in the two zones. In the unimodal zone, El Nino events are associated with a depression of the August peak in rainfall, but a lengthening of the season, potentially providing an opportunity for growing later-maturing crops. At bimodal sites, there is very little impact in August but November rainfall is enhanced in El Nino years and depressed in La Nina years. Given a forecast of ENSO, the primary strategies that will be useful in farm management will differ by rainfall zone and will revolve around the choice of crop or cultivar and the timing of planting in order to make optimal use of the growing period. Copyright © 2000 Royal Meteorological Society

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