Its topography is very rugged, with narrow valleys intersected by rivers and steep hills. Elevations in the park range from above sea level, and 60 percent of the park has an elevation of over . The highest elevation is Rwamunyonyi Hill at the eastern edge of the park. The lowest part of the park is at its most northern tip. The forest is an important water catchment area. With a generally impermeable underlying geology where water mostly flows through large fault structures, water infiltration and aquifers are limited. Much of the park's rainfall forms streams, and the forest has a dense network of streams. The forest is the source of many rivers that flow to the north, west, and south. Major rivers that rise in the park include the Ivi, Munyaga, Ihihizo, Ishasha, and Ntengyere rivers, which flow into Lake Edward. Other rivers flow into Lakes Mutanda and Bunyonyi. Bwindi supplies water to local agricultural areas. Bwindi has a tropical climate. Annual mean temperature ranges from a minimum of to a maximum of . Its annual rainfall ranges from . Peak rainfall occurs from March to April and from September to November. The park's forest plays an important role in regulating the surrounding area's environment and climate. High amounts of evapotranspiration from the forest's vegetation increases the precipitation that the region outside the park receives. They also lessen soil erosion, which is a serious problem in south-western Uganda. They lessen flooding and ensure that streams continue to flow in the dry season. Biodiversity The Bwindi Impenetrable Forest is old, complex, and biologically rich. Diverse species are a feature of the park, and it became an UNESCO World Heritage Site because of its ecological importance. Among East African forests, Bwindi has some of the richest populations of trees, small mammals, birds, reptiles, butterflies, and moths. The park's diverse species are partly a result of the large variations of elevation and habitat types in the park, and may also be because the forest was a refuge for species during glaciations in the Pleistocene epoch. The park's forests are afromontane, which is a rare vegetation type on the African continent. Located where plain and mountain forests meet, there is a continuum of low-altitude to high altitude primary forests in the park, one of the few large tracts of East African forest where this occurs. The park has more than 220 tree species, and