Analysis of the 1998 to 2005 drought over the northeastern highlands of Tanzania

Extreme weather and climate events have major negative effects on Tanzania's economy. Recently, the prolonged drought from 1998 to 2005 caused devastating crop failures, livestock losses and reductions in the country's water reservoir levels, which, in turn, created food shortages and rationing of hydroelectric power and water. The present study analyses the atmospheric circulations associated with the 1998 to 2005 drought that affected the northeastern highlands of Tanzania. Analysis of large-scale circulation indicates that the drought during the October to December (OND) short rainy seasons, from 1998 to 2005, was related to westerly low-level moisture flux divergence and subsidence over northern Tanzania associated with an eastward shift of the Walker cell. For the March to May (MAM) long rainy seasons, the prolonged drought was related to strong moisture flux divergence over the region and subsidence associated with the occurrence of the descending branch of a Walker-type circulation over the region. Rainfall onset was undefined for most years in both the OND and the MAM seasons, and, in all cases, unevenly distributed rains with prolonged dry spells were experienced in a shorter than average rainy season. However, an out-of-season rainfall peak occurred in January, after the end of the OND rains. This delayed peak has important implications for agricultural and water resource activities. The circulation patterns observed in the Tanzanian region from 1998 to 2005 were similar to those experienced during a previous prolonged drought (1973 to 1976), suggesting that some predictability of drought may exist.