Drought pattern along the coastal forest zone of Tanzania

Abstract

This study focused on identifying drought patterns particularly during the growing seasons along the coastal zone of Tanzania in order to facilitate the determination of drought impacts on forest Ecosystem. The growing seasons were March, April and May (MAM) referred as long growing season and October, November and December (OND) which is known as short growing season. The main data were precipitation from 16 weather stations covering the coastal zones of Tanzania. Standardized Precipitation Index (SPI) was used to establish meteorological drought patterns. The duration of records was between 34 and 59 years depending on the available data on the concerned stations. The SPI time series of 3 and 12 months showed that the coastal region of Tanzania experienced frequent drought conditions ranging from mild, moderate, severe and extreme droughts during both short and long growing seasons. It was found that the coastal zone of Tanzania experienced higher drought duration, severity and intensity with frequent extreme events after 2000 than before. Despite that Kisarawe area revealed low frequency of drought events (88%) than other study areas; it exhibited greater frequency of extreme droughts (46%) over the whole study areas. Higher drought duration (40 months) and severity (sum of SPI −36) were observed for precipitation data from Unguja Islands, while data from Julius Nyerere International Airport areas displayed higher drought intensity (SPI value of −1.9). Generally, Tanzania coastal zone was never completely without drought or anomalously wet conditions at any time scale during the period of record. The coastal zone was nearly entirely in drought periods especially the last decade after 2000. This suggests that vegetation in the coastal zone might have experienced the impacts of these droughts within the period. The magnitude of the impacts will be understood by tracking changes of biomass and forest cover along the coastal zone within the last decade from 2000 to 2011 in addition to the 1990/92 which experienced drought dominance for Pemba.