Local climate
As the Equator runs across Kenya at some 110 km to the north of Naivasha (Latitude of the lake: 0.45' S), the lake basin enjoys a typical equatorial climate with its characteristic high irradiance and high potential evaporation all year 'round, mitigated by its moderately high altitude, which can be felt during typically cool early mornings (8-10°C). The diurnal temperature excursion can be relatively high when not mitigated by the presence of trees, with early afternoon maxima reaching over 28°C.
Due to the influence of northerly marine currents running along the Indian Ocean coastline, the 'metereological equator' is slightly displaced further south, so that the seasonal alternance of temperatures reflects more closely a cycle that is typical of the southern hemisphere, with distinctively cooler temperatures occurring during the European summer and heat waves occurring in January.
Rainfall is distributed according to two main seasons: the Long rains of March-May and the Short rains of September-October. The lake is situated in a rain shadow position in respect to the predominant direction of the rains that typically arrive from the east; therefore rainfall over the lake itself is far more moderate than what precipitates over the eastern highlands, where average annual rainfall can be > 2000 mm. At the lake side, potential evaporation is comprised between 1500 and 1800 mm/year and is in excess of average yearly rainfall, which is around 700 mm.
The presence of several lakes streamlined along the eastern branch of the Great Rift has important consequences for the climate within this region. The rainfall within lake basins is enhanced by evaporation from the lake surface and by a daily cycle of convective rain; sometimes this can increase by as much as 30% the rainfall received by the basin, in the case of very large lakes such as Lake Victoria. Convective rains have an important role in producing an afternoon cooling of the water surface, which tends to mix the water column down to several metres. At Lake Naivasha, due to a combination of afternoon winds and frequent convective rainfall, surface water is mixed down to 9-10 m depth. Strong wind-storms occur between August and October, the period that coincides with the arrival of the monsoon.
