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Kenya - Climate

The weather changer known as El Nino left countries in east Africa in danger of famine. El Nino is the natural warming of parts of the Pacific Ocean that changes weather worldwide. El Nino occurs every several years and lasts close to a year. In 2015 El Nino mostly helped conditions in Kenya, Rwanda, Burundi, Uganda and Tanzania by creating more rainfall.

The drought that had been developing in regions of Somalia and Kenya over 2016 reached a stage of extreme concern by early 2017. The second rainy season, which typically lasts from October to December, began late and ended early in 2016, leaving total rainfall amounts far below average. Rivers and other surface water sources have dried up. Consequently, water access had decreased– pastoralists in the region are an average distance of 3-6 miles from the nearest water source—and water prices have more than tripled.

Due to drought, northern pastoralists were illegally bringing tens of thousands of cattle to private and community lands in search of water and grazing lands, often bringing them into conflict with landowners, and displacing wildlife.

It was not just a drought that is based on climatic conditions, Frank Pope, CEO of Save the Elephants, argued. “This is a drought based on chronic overgrazing of this ecosystem,” said Pope. “We’ve got several different data streams showing us the dramatic degradation that northern Kenya has suffered, and I think the same holds true for many other areas in Kenya where we’ve had too many livestock on the ground, exerting huge grazing pressure on the ground. About three-quarters of the northern rangelands is now at or below the level of organic soil carbon required for plant growth.”

With two-thirds of its landmass already desert or semi-desert, Kenya is vulnerable to low rain-fall. Less reliable weather patterns associated with climate change, as well as increasingly frequent La Ninas and El Ninos, mean that farmers now have less time to recover in between extreme weather events, such as droughts and floods.

Kenya is characterized by highly varied terrain and climatic conditions that range from moist to arid. Because industry had been entirely in the hands of non-Africans (chiefly Europeans) during the colonial era, most of it had been located in Nairobi and its neighboring towns, which had conditions congenial to Europeans, and to a lesser extent in Mombasa (despite its uncomfortable climate) because of its significance as a port.

A little less than 15 percent of Kenya's total area receives an annual rainfall of 760 millimeters or more. Still less of the country — between 12 and 14 percent — can expect an average rainfall between 560 and 760 millimeters a year. More than 70 percent of the area usually records less than 560 millimeters annually, and a considerable part receives less than 250 millimeters annually.

Mean monthly rainfall is often erratic, and annual variations are striking and can be serious, especially in drier areas. Thus at Lodwar in northwestern Kenya, where the mean annual rainfall is about 150 millimeters, as much as 500 millimeters and as little as 25 millimeters have been recorded in a year. Droughts affecting all of Kenya, but especially its drier areas, have occurred on the average every eight to 10 years for a period of two to four years. Among the factors responsible for the geographic variation in rainfall are the variations in topography and the sources and flow of the major air masses overhead.

Very important locally are the diurnal temperature changes associated with Lake Victoria. The principal air masses are the northeast and southeast trade winds, which vary in intensity and direction. Usually by late December the northeast trade winds flowing from the Arabian Peninsula (and on the west from the Sahara) being a dry season that lasts until about March. During March southeast trade winds sweeping across the Indian Ocean begin to deposit rain over Kenya, and in April rainfall occurs throughout the country. By July a second period of dry weather ensues—except in the western parts of the country. Dry conditions then prevail until September or October, when a reinstatement of the low-pressure belt over Africa and convergent trade winds bring what are known in Kenya as the small rains. These continue into December, when the seasonal cycle starts again.

The relative difference in temperature gain and loss and in altitude between Lake Victoria and the surrounding land results in the area between the lake and the Kenya Highlands' receiving at least two inches of rain in every, or almost every, month of the year and in the absence of a pronounced dry season. The effects of the larger air masses are still felt, nonetheless, and periods of higher rainfall are regularly recorded in April and December. To the north of this area, regional conditions also result in a wet season that lasts usually from March to September or October and a drier or dry period during the intervening months.

There are great variations in average temperatures, and altitude again is a major factor. The Kenya Highlands offer a cool, bracing climate, much of the highlands having a mean annual maximum temperature between 22°C and 26°C and a minimum between 10°C and 14°C. Nairobi, at 1,658 meters, has a mean annual temperature of about 18°C. The humidity in the highlands is about 90 percent in early morning. By midafternoon it drops substantially to about 40 percent in the dry season and to between 50 and 60 percent in the rainy season. The combination of moderate temperatures, adequate rainfall, and good soils brought tens of thousands of white settlers to the highlands during the colonial era.

Away from the highlands, as the elevation decreases, average temperatures increase. A zone immediately around the highlands has mean annual maximum temperatures between 26°C and 29°C and minimums between 14°C and 18°C. Beyond this zone the low plateaus of eastern Kenya and the northern plains register mean annual maximums between 30°C and 34°C and minimums from 18°C to over 22°C. One area to the west of Lake Rudolf and another along the Somalia border have mean maximum temperatures above 34°C; the latter area has recorded an absolute maximum of 46°C. The Rift Valley experiences temperatures similar to those in eastern Kenya. The humidity in the semiarid to arid areas usually is between 60 and 70 percent in early morning. It decreases by midafternoon to roughly 40 to 45 percent and in some places to as low as 30 percent.

A zone along the coast experiences both high temperatures and high humidity. The hottest months are January through March; at Mombasa the mean monthly temperature is about 28°C during this time. Beginning in June and extending through August, a cooler period sets in when afternoon temperatures may average about 28°C and night temperatures may drop to below 21°C. Little variation occurs, however, in the humidity, which throughout the year is above 90 percent early in the morning and usually between 60 and 70 percent in midafternoon. Sea breezes blow relatively steadily during the year, providing some relief.

The principal drainage pattern centers in the Kenya Highlands Region, from which streams and rivers radiate eastward toward the Indian Ocean, westward to Lake Victoria, and northward either to Lake Rudolf or to the arid terrain of northern Kenya, where they disappear. A secondary drainage system is formed by rivers in the southern highlands of Ethiopia, which extend into Kenya along the eastern section of their boundary. These rivers are all seasonal, and those that receive sufficient water at flood times to reach the sea do so through Somalia. Minor internal systems are associated with the lakes in the Rift Valley.

The two largest perennial rivers, and the only navigable ones, are the Tana and the Galana (the latter known locally in its course from west to east as the Athi and the Galana), both of which empty into the Indian Ocean. The Tana River, approximately 725 kilometers long, rises in the southeastern part of the Kenya Highlands and enters the sea at Kipini. About 320 kilometers of the Tana's lower length are navigable by shallow-draft launches.

The Tana basin includes much of the flow from the Aberdare Range and Mount Kenya. In the Tana River's lower reaches the gradient is extremely gentle, banks are low, and flooding occurs during high water. As the river nears the coast, it develops many backwaters and at times may change course. The upper course of the river has a number of falls that have the potential, partially exploited by the early 1980s, for hydroelectric power development.

The Galana River rises in the southeastern part of the Kenya Highlands and with its tributaries flows into the Indian Ocean north of Malindi. It is navigable by canoe for approximately 160 kilometers inland, where further travel is impeded by the rapids of Lugards Falls. Several smaller rivers originate in the foothills of the eastern Kenya Highlands area within the Tana River basin. They usually disappear in the semiarid region east of the highlands but at times of heavy flooding manage to cross the area and empty into the Tana River. South of the Galana River, the Goshi River (called the Voi in its upper course) has a length of about 210 kilometers, but only about 80 kilometers of the lower course is perennial.

The western slopes of the Kenya Highlands are drained by a number of generally parallel rivers that empty into Lake Victoria. The largest rivers include the Nzoia, which drains the Cherangany Hills and the eastern slope of Mount Elgon, and the Yala, which eventually reaches the lake through Lake Kanyaboli and the Yala Swamp. Yala Falls and Selby Falls on a tributary of the Nzoia have considerable hydroelectric power potential. The Mara River, having its source in the Mau Escarpment in the southwest part of the highlands, flows southward, enters Tanzania, and turns westward to Lake Victoria.

The northern part of the Kenya Highlands east of the Rift Valley is drained by small rivers that disappear in the arid land to the north and by the larger, eastward-flowing system of the Ewaso Ng'iro. The Ewaso Ng'iro usually terminates in the great Lorian Swamp in the Tana Plains, but at times a heavy runoff floods the swamp, and the waters flow eastward as the Lak Dera into Somalia.

“For the first time since 1961, several desert locust swarms invaded northeastern Kenya,” reported Locust Watch, a branch of the Food and Agriculture Organization of the United Nations, on December 3, 2007. Swarms of locusts are dangerous because they can move quickly over long distances, destroying crops and all other plants growing in their path. Locusts form densely packed groups, or swarms, when an ample supply of food and water allow a large number of the insects to hatch and breed. Because swarms tend to form in remote parts of Africa and southwest Asia, scientists use satellite data to identify areas where conditions are right for desert locusts.

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Page last modified: 03-06-2017 18:14:54 ZULU