Frequency of wet and dry spells in Tanzania

Forty one years of daily data (1960-2000) have been used to investigate the spatial and temporal distribution of wet and dry spells during the rainfall seasons of Tanzania. The frequency characteristics of wet and dry spells were based on the threshold of 1.0 mm of daily rainfall events. The observed frequency of wet and dry spells during the rainfall seasons over the period of study showed that at both bimodal and unimodal locations the frequency of occurrence of one-day wet and dry spell was highest at all locations then reduced smoothly as the length of the season progress. The analysis gave an indication that the longest run of wet spell of 25-days occurred during March - May rainfall season at Lushoto over the north eastern highlands on the bimodal regime. Similarly, longest run of wet spells of 28 days was also observed at Mbeya and Mahenge over the southwestern highlands on the unimodal regime. Longest dry spells run were noted over the semi and parts of Tanzania including Dodoma, which registered the longest run of 249 days that occurred in 1999 and coincided to a cold El Nifio-Southern Oscillation (ENSO) event.