Climate of Mount Kenya
The climate of Mount Kenya has played a critical role in the development of the mountain, influencing the topography and ecology amongst other factors.
The area around Mount Kenya is covered by a comparably large number of weather station data with long measurements series and thus the climate is well recorded.
The altitude and aspect of the watersheds and main peaks results in the north side of the upper mountain being in summer conditions.
The low pressure belt around the equator known as the Intertropical Convergence Zone (ITCZ) is responsible for the wet and dry seasons of Mount Kenya.
[7] At all times of year except around January, a low pressure situated over Tibet drives winds in a horseshoe shape from the Indian ocean, over eastern Africa and then towards India.
Large daily temperature fluctuations occur which led Hedberg to exclaim winter every night and summer every day.
[9] The anabatic winds caused by warm rising air gradually bring these clouds to the summit region in the afternoon.
This daily cover of cloud protects the glaciers on the south-west of the mountain which would otherwise get direct sun every day, enhancing their melt.
[10] The upwelling cloud eventually reaches the dry easterly air streams and dissipates, leading to a clear sky by 5pm.
[13] This effect means the lapse rate during the day on Mount Kenya is lower than average for dry air.
At night the lapse rate is again lower than average for dry air due to the katabatic winds from the glaciers.
Lower down, in the dry season, dew every morning has a similar role, and it is estimated that the majority of the small streams are fed in this way.
[13] Past climate is interpreted using a number of methods including lake levels, river strength, dune systems, glacial extent and pollen.
Problems associated with going back a long time include an uneven distribution of records and a shortage of vegetation fossils due to unfavourable conditions.
[16] Over long time scales, climate is controlled by Milankovitch cycles changing the amount of solar radiation reaching the earth.
[19] Since the start of the Quaternary period the northern hemisphere has undergone 21 major ice ages and this signal is also present in East Africa.
[20] During the last glacial maximum, 20,000 years ago, the European Ice Sheet would have diverted the Atlantic weather systems over Kenya.
[20] Over the past 6,000 years Mount Kenya has had a series of at least six minor glacial advances as well, with the final maximum at the end of the little ice age in 1900.
[22] An alternate explanation is that given the timescale of millions of years, the probability of tornados transporting flora and fauna between mountains is high.
[12] 5 mya the Mediterranean Sea was dry[23] and the dunes of the Sahara were much further south; the area that is now Kenya was an arid savanna.
Near the end of this cold phase the first Heinrich event (H6) occurred, releasing a mass of ice into the north Atlantic 66 kya.
[25][26] A series of Heinrich events followed, with an associated drying of the East African climate at 50, 35, 30, 24, 16 and culminating with the Younger Dryas period 12kya.
[27] The Last Glacial Maximum (LGM) occurred 23–14.5 kya with a very arid phase in Africa when desert extended hundreds of kilometres (miles) further south than present.
[16][27] High altitude vegetation was mainly limited by temperatures and not drought, again implying a wet climate.
[27] After 5 kya the monsoon began to gradually weaken[30] and the East African climate became similar to present day, but slightly colder and drier.
There was a temperature minimum over 3.7-2.5 kya and also during the little ice age spanning the years 1300-1900 when a permafrost regime dominated on Mount Kenya.
[21] Mount Kenya used to be covered in an ice cap, which eroded the mountain to expose the volcanic plugs which form the current summit.
[10] Palaeobotany relies on the fact that each ecosystem is characterised by certain plants, which in turn act as a proxy for climate by knowing which modern habitats they occur in.
The core shows an abrupt jump of pollen specimens at 11,000 years, corresponding with the Younger Dryas stadial in Europe.
Following the introduction of Hagenia, other tree species started appearing until the lake was situated in full montane forest at 5,000 years before present.
