Kenya

Kenya lies astride the equator on the eastern coast of Africa. It is a medium-sized country by continental standards; covering an area of about 586,600km sq. Inland water bodies cover some 10,700km sq, the bulk of this in Lakes Victoria and Turkana.Kenya is bordered by Somalia and the Indian Ocean to the east, Ethiopia to the north, Sudan to the northwest, Uganda to the west and Tanzania to the south. The coastline, about 550km long, faces the Indian Ocean.

Kenya has tremendous topographical diversity, including glaciated mountains with snow-capped peaks, the Rift Valley with its scarps and volcanoes, ancient granitic hills, flat desert landscapes and coral reefs and islets.

However, the basic configuration is simple. Coastal plains give way to and inland plateau that rises gradually to the central highlands, which are the result of the relatively recent volcanic activity associated with the formation of the rift valley.

To the west the land drops again to the Nyanza plateau that surrounds the Kenyan sector of Lake Victoria; and to the north, to the rugged low country around Lake Turkana.

The coastline is broken and composed of beaches, coral cliffs and reefs, creeks and numerous offshore coral islands. Inland, a mainly level but narrow coastal plain lies on sedimentary rocks, with some igneous intrusions such as Dzombo and Mrima. Beyond low rolling hills lies the so-called Nyika Plateau, mainly on sedimentary rocks.

This landscape covers almost the entire northeastern sector of the country, on very gradual slopes.

The Great Rift Valley, with its associated escarpments and mountains, is a major feature. It runs the length of the country from Lake Turkana in the north to Lake Natron on the southern border with Tanzania.

The central portion of the rift is raised, with the Aberdare Mountains and Mt Kenya to the east and the Mau Escarpment and Cherangani Hills to the west. The northern and southernmost sectors of the rift are low-lying, arid and rugged, with spectacular volcanic landforms.

The region west of the central highlands is characterized by Precambrian metamorphic rocks and linear basement hills. Mt Elgon, an old, eroded volcano, intrudes through the ancient shield on the Uganda border. The lake Victoria basin generally has a gently sloping landscape and an eroded surface that exposes granitic outcrops.

Isolated hills and mountains, such as Mt Kulal, Mt Nyiro and Mt Marsabit, are scattered to the north and east of the central highlands. The Taita Hills, rising from the southeastern plateau, are ancient fault-block formation, the northernmost of a chain of isolated peaks (the ‘eastern arc’) that stretches south to Malawi through eastern and southern Tanzania.

They sit almost cheek-by-jowl with one of the region’s recent volcanic ranges, the Chyulu Hills.

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 plateau 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 C.

Kenya’s natural vegetation is as diverse as its climate and topography would suggest. Dean & Trump (1983) mapped 19 distinct biotic communities; some of which can be lumped under general headings. Afro-alpine moorland (1.2 % of total land area) occurs above c. 3,000 m, on Mt Kenya and Mt Elgon, the Cheranganis and the Aberdare Mountains.The vegetation is sparse at the upper levels (above c.3, 800 m), with species of giant Lobelia and Senecio; below this is grassland and Erica shrubland, often with stands of Hagenia abyssinica in sheltered spots.

Highland grassland (0.05%) occurs above c.2,400 m on either side of the central Rift Valley (in the Kinangop and Mau Narok / Molo Grasslands. This restricted habitat is not covered in any protected area and is one of the most endangered in Kenya.

Many tussock-forming grass species occur. Other important grassland types include fire-induced grassland (3.1 %, e.g. parts of the masai Mara) and seasonal floodplain and delta grassland (4.7%, e.g. the Tana river Delta). Grassland also occurs on alkaline volcanic ash (0.2%), e.g. to the south of the Chyulu Hills.

Highland moist forest (2.0%) occur between c.1, 500 m and 3,000m in areas that receive rainfall of more than 1,200 mm per year. A mosaic of forest and bamboo Arundinaria alpina is often present at the higher levels.

Typical montane forest trees include species of Podocarpus, Olea, Juniperus and Newtonia, but the forest type varies greatly according to altitude and rainfall.

Relicts of Guineo-Congolian rainforest (0.1%) occur in western Kenya, in and around Kakamega Forest. Despite its relatively high altitude (1,600m), in terms of biogeography Kakamega is the easternmost outlier of the great tract of tropical rain forest that once extended across equatorial Africa.

The average annual rainfall is over 1,900 mm, and typical tree species include Celtis, Aningeria, croton, Fagara and Manikara. The North and South Nandi Forests are transitional between the Guinea-Congolian and Montane forest forest types.

Several types of coastal forests and woodland (0.1%) characteristic of the Zanzibar-Inhambane Mosaic vegetation region, occur along the narrow coastal strip.

These patches are mainly small and relictual, and the forest structure and composition vary greatly according to soil type and rainfall. Characteristic trees include Cynometra, manikara, Afzelia, Brachylaena and Brachystegia.

Coastal evergreen bushland (0.4%) also occurs, in a mosaic with cultivated land; this is almost always a secondary vegetation type . Coastal palmstands, often in tall grassland, are a rare vegetation type covering ess than 3.1% of the land area.

They are concentrated near the Ramisi River in the south, and around the Tana River Delta in the north. Elsewhere, highland dry forests (0.4%) occur on hilltops that attract mist and rain (e.g. Mt Marsabit and the Taita and Chyulu Hills. Riverine forests (e.g. along the Mara River) and groundwater forests (e.g. Kitovu) together make up c.1.5% of the land area.

Thorn bushland and woodland are the most extensive vegetation types in Kenya (41.7%), running from Amboseli in the south through the Tsavo parks to north-east and north-west Kenya.

Characteristic tree species are Acacia, Commiphora ssp., while grasses include species of Hyparrhenia, Digitaria and Themeda. This habitat often contains concentrations of large mammals and many large protected areas are in this vegetation zone. It is often favourable for ranching and pastoral land. This vegetation grades into semi-arid wooded and bushed grassland (0.2%).

The north-central and northwestern parts of the country are covered by semi-desert (16.8%) with characteristic shrubby thornbush species, mainly Acacia. In places, such as the Dida Galgalu and Chalbi deserts and around Lake Turkana, areas of barren land (0.4%) occur, with very little vegetation. Marine beaches and dunes make up another 0.04% of the land area.

Wetlands are an important habitat in Kenya, covering about 14,000 km sq of the country’s land surface (Crafter et al. 1992). Strongly alkaline Lakes (0.04%), mainly in the Rift valley, lack macrophytes, except at river inflows, but may have large blooms of microscopic plants – notably the cynaophytes Spirulina spp.

Papyrus swamps, consisting largely of stands of cyperus papyrus, are found patchily around the shores of Lake Victoria, mainly along river inflows. Elsewhere this habitat is widely scattered, with notable patches at Lake Naivasha and Lake Jipe. (Only Lake Victoria’s papyrus holds the suite of bird species specialized on this habitat) Swamps of other Cyperus species, Typha and Phragmites occur locally but are rarely of any great size.

Permanent swamps make up 0.11% of the land area, while bodies of freshwater cover 2.1% fo Kenya’s surface area.

Mangrove swamps (0.2%) occur along parts of the Kenyan shoreline, especially in sheltered creeks and estuaries. Eight species of mangrove occur, the commonest of which is Rhizophora mucronata. Lamu district has the country’s most extensive mangrove swamps.

On sandy shorelines are often beds of seagrass (some twelve species are recorded), beyond the littoral zone or in deeper channels within it. Coral reefs and islands make up some 59,000 ha, or 0.1% of the land area. Human-modified habitats, created at the expense of the natural vegetation, occur throughout the country but especially in the highlands.

These include cultivated land under a wide variety of crops (18%), plantations of exotic trees, secondary thicket and scrub, eroded and de-vegetated woodland and bushland, and overgrazed pastureland.

All Kenya’s major river drain from the central highlands, divided by the rift into those flowing westwards into Lake Victoria and those flowing eastwards towards the Indian Ocean.There are five major drainage basins: Lake Victoria, the Rift Valley, the Athi-Galana-Sabaki River (and Coastal areas to its south), the Tana River and the northern Ewaso Ng’iro.

Kenya only has a small part of Lake Victoria’s water surface, but the Kenya catchment contributes a disproportionate 33% of its surface inflow, some 470 million cubic meters a year. The rift valley contains several basins of internal drainage, forming a chain of endorheic lakes from Lake Natron on the Tanzanian border, through Lakes Magadi, Naivasha, Turkana, Elementaita, Nakuru, Bogoria and Baringo.

These lakes vary in alkalinity; from fresh water Lake Naivasha to the intensely alkaline Lake Magadi. Lake Turkana is notable as a major volume of (more or less) fresh water in an otherwise arid and barren part of the county, while a number of rivers, including the Turkwel, Kerio, Athi-Galana, Tana and Northern and Southern Ewaso Ng’iro, flow for long distances through dry parts of the country.