Africa is faced with three major issues where the atmosphere is concerned, namely:
Rainfall records from the early 1900s to mid-1980s show that Africa's
average annual rainfall has decreased since 1968, and has been fluctuating
around a notably lower mean level, as shown in Figure 2a.2 (UNEP 1985).
There is also some evidence that natural disasters have increased in frequency
and severity over the past 30 years, particularly drought in the Sahel
Climate variability means the seasonal and annual variations in temperature and rainfall patterns within and between regions or countries. For Africa, it is determined by prevailing patterns of sea surface temperature, atmospheric winds, regional climate fluctuations in the India and Atlantic Oceans, and by the El Niņo Southern Oscillation (ENSO) phenomenon-the natural shift in ocean currents and winds off the coast of South America which occurs every two to seven years. ENSO events bring above average rainfall to some regions and reduced rainfall to others.
Africa is characterized by considerable climatic variations, both spatial and temporal, and extreme events such as flooding and drought have been recorded for thousands of years (Verschuren, Laird & Cumming 2000). The equatorial belt generally has high rainfall, whereas northern and southern African countries and those in the Horn of Africa are typically arid or semi-arid (see Figure 2a.1). All parts of Africa, even those that usually have high rainfall, experience climatic variability and extreme events such as floods or droughts. Most of Eastern, Central and Southern Africa, as well as the Western Indian Ocean Islands, are affected by the ENSO phenomenon. The 1997-8 ENSO triggered very high sea surface temperatures in the south-western Indian Ocean causing high rainfall, cyclones, flooding and landslides across most of Eastern Africa whereas south-western Africa experienced drier conditions. The higher sea temperatures also caused extensive bleaching of corals on the Eastern African coast and in the Western Indian Ocean Islands (Obura, Suleiman, Motta, & Schleyer 2000, PRE/COI 1998).
Rainfall records from the early 1900s to mid-1980s show that Africa's average annual rainfall has decreased since 1968, and has been fluctuating around a notably lower mean level, as shown in Figure 2a.2 (UNEP 1985). There is also some evidence that natural disasters have increased in frequency and severity over the past 30 years, particularly drought in the Sahel (OFDA 2000). The most prolonged and widespread droughts occurred in 1973 and 1984 (when almost all African countries were affected) and in 1992, although in this case drought was mainly restricted to Southern Africa. The impacts of the 1984 and 1992 droughts were alleviated to some extent by increased preparedness of some countries, even though the droughts themselves were more severe (Gommes & Petrassi 1996). Countries most regularly affected by drought include Botswana, Burkina Faso, Chad, Ethiopia, Kenya, Mauritania and Mozambique (FAO 2001a).
Human activities such as deforestation and inappropriate management of land and water resources can contribute to the frequency and impacts of natural climatic events. For example, clearing of tropical forests in Central and Western Africa alters local climate and rainfall patterns and increases the risk of drought. Clearing of vegetation increases run-off and soil erosion, and damming of rivers and draining of wetlands reduces the environment's natural ability to absorb excess water, increasing the impacts of floods.
Africa's people and economies are heavily dependent on rain-fed agriculture (for commercial export and subsistence) and are therefore vulnerable to rainfall fluctuations. It is usually the poor who suffer most from flood- or drought-induced crop failure, as they are forced to cultivate marginally productive land and cannot accumulate reserves for times of hardship. Malnutrition and famine have resulted from both droughts and floods in Africa and associated food imports and dependency on food aid have contributed to limited economic growth of the countries affected. Additional impacts include loss of infrastructure and disruption of economic activities, outbreaks of disease and sometimes population displacements, both internal and international. Over the past 30 years, millions of Africans have sought refuge from natural disasters, often settling in fragile ecosystems and/or experiencing social tensions with neighbouring communities. Ecological impacts of drought and flooding include land degradation and desertification, loss of natural habitat or changes in distribution of biodiversity, increased soil erosion and silting of rivers, dams, and coastal ecosystems.