Kenya is generally a dry country;
over75% of its area is classed as arid of semi-arid with only around 20%
being viable for agriculture. Inland, rainfall and temperatures are closely
related to altitude changes, with variations induced by local topography.
Generally the climate is warm and humid at the coast, cool and humid in the
central highlands, and hot and dry in the north and east.
Across most of the country, rainfall is strongly seasonal,although its
pattern, timing and extent vary greatly from place to place and from year to
year. The relatively wet coastal belt along the Indian Ocean receives 1,000
mm or more rain per year. Most rain falls from April to July as a result of
the southeasterly monsoon. Another moist belt occurs in the Lake Victoria
basin and its surrounding scarps and uplands, mainly due to moist westerly
winds originating over the Atlantic Ocean and Congo Basin. Except
immediately adjacent to the Lake, rainfall occurs reliably from March to
November. The upland plateaux adjacent to this area are less influenced by
the lake, and rain falls mainly in March-May and July-September. In much of
the central highlands, there is also a bimodal rainfall pattern, with rainy
seasons in March-May and October-December. The remaining 70% or so of the
land area falls into the 'arid lowlands' zone (NRI 1996), with rainfall
averaging less than 500 mm and varying greatly from year to year. Rainfall
peaks in most areas are in November and April. Some 30% of this zone can be
classed as semi-desert, with rainfall averaging less than 300 mm per year
and evaporation often greater that 3,000 mm.
Except for the coast and Lake Victoria region, altitude is the main
determinant of precipitation. The high-attitude areas (over c. 1,500 m) in
the central Kenya highlands usually have substantial rainfall, reaching over
2,000 mm per year in parts of the Mau Escarpment. However, topography also
has a major influence, with strong rain-shadow effects east of Mt. Kenya and
the Aberdare mountains. Here, even areas higher than 1,800 m may be
relatively dry. In the arid lowlands the peaks of isolated mountains attract
cloud and mist, and may support very different vegetation to that of the
surrounding plains.
Differences in temperature vary predictably with altitude. Frost occurs
regularly at 3,000 m and occasionally down to at least 2,400 m, and there is
permanent snow and ice on top of Mt. Kenya at 5,200 m. The hottest areas are
in the arid northeast, and west of Lake Turkana, where mena maximum
temperatures average over 34 oC.
