Analysis of rainfall variations and trends in coastal Tanzania

Abstract

Rainfall in coastal Tanzania has been investigated for their variability and trends from seven key weather stations during the last 50 years (1960-2009). Results indicate that the island of Mafia receives the highest amount of rainfall (1879 mm/yr) while Kilwa Masoko receives the lowest (1029 mm/yr). Generally, precipitation in the islands is heavier than on the mainland coast due to moisture convergence in sea breezes. The monthly series indicate predominance of annual and semi-annual oscillations in the northern sector, while in the southern coast the annual signal is the most dominant. Partial correlation analysis revealed a significant influence of the El-Niño Southern Oscillation (ENSO) on annual rainfall. However, the effects of the Pacific Decadal Oscillation (PDO) and the Indian Ocean Dipole (IOD) are relatively smaller. In the seasonal timescale, the effects of the large scale climatic phenomena are relatively smaller during the rainfall and Northeast (NE) monsoon seasons, but are significantly larger during the Southeast (SE) monsoon. Linear regressions of the monthly rainfall series portray a general downfall trend at each station, but all the trends are insignificant. The inter-annual and decadal variations show that the year 2003 and the last decade (2000-2009) were generally the driest in the last half century.