Fluctuations in the Rainfall of the Serengeti Ecosystem, Tanzania

Two sets of daily rainfall figures, and eleven sets of monthly figures from East Africa have been analysed on a time basis. The daily figures show a weak cycle correlated with the lunar month, and also a 3-day cycle which is probably caused by the local rain-forming processes. The monthly figures show a dominant annual cycle. The annualfiuctuations are fairly well correlated over a wide area. There are small and rather variable cycles of around 5 and 10 years in duration, and possibly also of 20 and 40 years. The 5-year cycle is negatively correlated with changes in sunspot activity 1-3 years later. It is suggested that these variations in rainfall are caused by changes in the general atmospheric circulation. The possible ecological effects of the observed changes are briefly discussed.