Examining the Temporal Characteristics of Rainfall Over Zanzibar Islands

Abstract

This study aimed to examine the temporal characteristics of rainfall over the Zanzibar Islands from 1974 to 2021. The specific objectives were to examine the variability of rainfall and determine the long-term trends, determine the onset, cessation, and duration of rainfall, as well as the signal of climate changes in Zanzibar. The study utilized daily rainfall data from 2012 to 2021, as well as monthly data from 1974 to 2021, collected from the Tanzania Meteorological Authority (TMA) Zanzibar office. The Mann-Kendall trend test, the arithmetic mean methodology, single mass curve analysis, and coefficient of variation were the key methodologies used. The R-Instat program was used to calculate rainfall onset, cessation, and duration. The study revealed both increasing and decreasing trends in rainfall across different stations at annual, seasonal, and monthly timescales. On an annual timescale, Pemba Airport showed a significant decreasing trend, whereas other stations exhibited statistically non-significant trends. The study also found that 2021 was an extremely dry year, especially on Unguja Island. Furthermore, the onset of the OND season was found to be more variable than the MAM season, indicating more unpredictability in the timing of rainfall. Furthermore, the signal of climate change was found, as demonstrated by the significant variability of rainfall characteristics such as onset, cessation, duration, and amount. The study suggested that early actions should be taken to mitigate the potential impacts of climate change over the Zanzibar Islands, including forest restoration initiatives and promoting renewable energy sources. Farmers should also be encouraged to use forecasts issued by the Tanzania Meteorological Authority (TMA) to improve agricultural planning and crop yields.