Freshwater Ecology of Kenyan Highlands and Lowlands
Chapter 16 Freshwater Ecology of Kenyan Highlands and Lowlands { { Dorothy Wanja Nyingi*, Nathan Gichuki and Mordecai O. Ogada *Ichthyology Section and KENWEB, National Museums of Kenya, P.O. Box 40658, Nairobi, Kenya {University of Nairobi, P.O. Box 30197, Nairobi, Kenya { Laikipia Wildlife Forum, P.O. Box 764, Nanyuki, Kenya 1 INTRODUCTION Kenya lies astride the equator, but the country experiences wide variations in climate. Freshwater ecosystems occur mainly in the narrow coastal plain, the central highlands and western parts of Kenya. These cover about 25%, while the rest of the country (75%) experiences arid or semiarid climate. The annual rainfall in the country averages 621 mm per year, but it varies seasonally and spatially. The amount of annual rainfall available to maintain freshwater eco- systems varies from a maximum of 750 mm in the dry areas to a maximum of 1700 mm in the coastal plain, the central highlands and Lake Victoria basin. Surface runoff and natural river flows as well as the rate of seepage of rainwa- ter are influenced by variations in intensity of rainfall, density of vegetation, type of soil and the presence or absence of wetlands. The headwaters of Kenya’s five primary catchment areas all arise in five indigenous montane forest areas commonly referred to as Kenya’s ‘water towers’ (Figure 1). The water towers, namely, Aberdare Range, Mount Kenya, Mount Elgon, Mau Complex and Cherangani Hills, have an average annual rainfall of 2300 mm and a potential rainfall–runoff ratio of 65%, which is more than 75% of the renewable surface water resources of Kenya (19,691 million m3 per year).
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