Causes of Drought

Figure 18.1 shows below-normal rainfall during different years that are often associated with droughts in Kenya. These rainfall deficits are caused by the anomalies in the circulation patterns that can extend from local or regional to very large scales. Some patterns that are responsible for spatial and temporal distribution of rainfall in Kenya include the Intertropi-

cal Convergence Zone (ITCZ), subtropical anticyclones, monsoonal wind systems, tropical cyclones, easterly/westerly wave perturbations, subtropical jet streams, East African low-level jet stream, extratropical weather systems, teleconnection with El NiƱo/Southern Oscillation (ENSO), and quasi-biennial oscillation (Ogallo, 1988, 1991, 1994). In addition, complex physical features such as large inland lakes, mountains, and complex orographic patterns (e.g., the Great Rift Valley) influence rainfall patterns. Lake Victoria in western Kenya is also one of the largest freshwater lakes in the world and has its own strong circulation patterns in space and time. These regional features often induce complex patterns of rainfall anomalies over the region and reduce the chances of extreme positive/negative anomalies occurring across the country.

Figure 18.2 shows that the larger amount of mean annual rainfall is concentrated over the mountain slopes and near the large bodies of water. More than 80% of Kenya may be classified as arid or semiarid lands (ASALs) with annual rainfall less than 700 mm (figure 18.3).

The arid land classification is based on the moisture index (Pratt et al., 1966), which ranges from -50 to -60 for very arid, from -40 to -50 for arid, and from -30 to -40 for semiarid land categories. Interannual rainfall fluctuations are common in all locations, but the highest variability is concentrated within the ASALs. Most of the annual rainfall is received during the two separate rainfall seasons (i.e., the March-May and October-December periods), with higher rainfall being in the first season. Agricultural practices are therefore tied to the seasonal nature of rainfall. Rainfall in many parts of Kenya is often skewed, and at times a large proportion of it falls early, even before the crop has been planted. Such rainfall is ineffective, being of little use to the young plants, which have underdeveloped root systems. Some locations to the west, however, receive a third rainfall peak during July-August, and some locations near the large bodies of water receive substantial rainfall throughout the year (figure 18.2).

Though floods occurred during 1997-98 (often attributed to El Nino), one of the longest and severest droughts in Kenya's history occurred from mid-1998 through 2001. The drought had harsh negative impacts on agriculture and livestock (figure 18.4), wildlife, tourism, water resources, and hydroelectric power generation.

The low water levels in the dams led to strict power rationing, which resulted in large losses to the economies. Water supplies for industrial and domestic consumption were not spared by the drought. There were serious water shortages both in urban and the rural areas. Lack of water and pasture led to severe conflicts between wildlife and pastoral communities. Similarly, lack of adequate power due to prolonged drought resulted in loss of employment and economic hardships. The government had to seek support from the international community to address the impacts.

Sometimes human practices contribute to droughts. For example, some farmers in the semiarid Laikipia district and Wakambas of East Province have introduced maize (a higher water-demanding crop) to replace a mark

Figure 18.1 Interannual variability of rainfall for standard seasons in Kenya.

Dec-Jan-Feb 1 .1

season, Kenya Coast

.1. Ii 1 1

l|""| l|l||l

1965 1970 1975

1995 2000

1965 1970 1975

1995 2000


Mar-Apr-May s 1 1,

eason, Central Rift Valley, Kenya

J. L 1 ,


M 1

1 nu

1965 1970 1975 1 980 1965 1 990 1995 2000

1965 1970 1975 1 980 1965 1 990 1995 2000

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Renewable Energy 101

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