Serengeti–Mara Rainfall Gradient

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A steep and persistent gradient in annual rainfall across the ecosystem, from roughly 400–500 mm a year on the south-eastern plains to as much as 1,200 mm a year in the north-west toward the Mara. It is produced by the rain shadow of the Ngorongoro Crater Highlands and the Meru–Kilimanjaro massif, which strip moisture from south-easterly winds coming off the Indian Ocean before they reach the plains. Boone, Thirgood and Hopcraft (2006) showed that wildebeest distribution can be modelled from rainfall and resulting new vegetation growth, which is the mechanism behind the claim that the migration follows rain and not a calendar.