2.3.1.6. Deserts

Deserts are an environmental extreme characterized by low rainfall that is highly variable intra-annually and interannually. Desert air is very dry; incoming solar and outgoing terrestrial radiation are intense, with large daily temperature fluctuations; and potential evaporation is high. Many organisms in the deserts already are near their tolerance limits (IPCC, 1996). The Sahara in north Africa and the Namib desert in southWest Africa are classified as the hottest deserts in the world-with average monthly temperatures above 30°C during the warmest months and extremes above 50°C. The diurnal temperature range often is large; winter nights in the Namib Desert sometimes are as cold as 10°C (IPCC 1996, WG II, Section 3.3.1) or lower. Extreme desert systems already experience wide fluctuations in rainfall and are adapted to coping with sequences of extreme conditions. Initial changes associated with climate change are less likely to create conditions significantly outside present ranges of tolerance; desert biota show very specialized adaptations to aridity and heat, such as obtaining their moisture from fog or dew (IPCC 1996, WG II, Section 3.4.2).

2.3.1.7. Mountain Regions

Mountains usually are characterized by sensitive ecosystems and regions of conflicting interests between economic development and environmental conservation. In Africa, most mid-elevation ranges, plateaus, and high-mountain slopes are under considerable pressure from commercial and subsistence farming activities (Rogers, 1993). Mountain environments are potentially vulnerable to the impacts of global warming. This vulnerability has important ramifications for a wide variety of human uses-such as nature conservation, mountain streams, water management, agriculture, and tourism (IPCC 1996, WG II, Section 5.2).

There is a general picture of continuing ice retreat on the mountains. On Mount Kenya, the Lewis and Gregory glaciers have shown recession since the late 19th century (IPCC 1996, WG II, Box 5-3). Changes in climate (as projected in Greco et al., 1994) could reduce the area and volume of seasonal snow, glacier, and periglacial belts-with a corresponding shift in landscape processes. The retreat of some glaciers on Kilimanjaro and Mt. Kenya would have significant impacts on downstream ecosystems, people, and their livelihoods because of moderation of the seasonal flow regimes of rivers upstream. Further reduction of snow cover and glaciers also could reduce the scenic appeal of African high mountain landscapes for tourists and thus have a negative impact on tourism.

Forest fires would increase in places where summers become warmer and drier. Prolonged periods of summer drought would transform areas already sensitive to fire into regions of sustained fire hazard. Mt. Kenya and mountains on the fringes of the Mediterranean Sea already subject to frequent fire episodes could be affected (IPCC 1996, WG II, Section 5.2.2.3).

2.3.1.8. Adaptation and Vulnerability

There is potential for spontaneous and assisted adaptation in Africa. Many options will need to involve a combination of efforts to reduce land degradation and foster sustainable management of resources. This section highlights options for forestry and woodlands, rangelands, and wildlife.

A number of adaptive processes designed to prevent further deterioration of forest cover already are being implemented to some degree. Some of these measures involve natural responses when particular tree species develop the ability to make more efficient use of reduced water and nutrients under elevated CO₂ levels. Other adaptive measures involve human-assisted action programs (such as tree planting) designed to minimize undesirable impacts. These strategies will include careful monitoring and microassessment of discreet impacts of climate change on particular species. Low-latitude forest adaptation options, especially in west Africa, must include active vegetation and soil management. For example, Gilbert et al. (1995) have indicated that silvicultural practices, endangered species habitat management, watershed manipulation, and antidesertification techniques could be applied given current infrastructure in Cameroon and Ghana. These adaptive measures will help reduce climate change impacts on forest watersheds and semi-arid woodlands. Smith and Lenhart (1996) have identified enhancement of forest seed banks as an adaptation policy option for maintaining access to a sufficient variety of seeds to allow the original genetic diversity of forests to be rebred. Genetic diversity also provides an assurance that benefits provided by forests are not lost forever (Smith and Lenhart, 1996) and is particularly relevant to the maintenance of the forests in the Sahel and other extremely sensitive regions of Africa where 20 years of recurrent drought have degraded the forests. Mwakifwamba (1997) asserts that adaptation strategies or measures in Tanzania should focus mainly on reducing high deforestation rates, protecting existing forests, and introducing new species or improving existing species.

For rangelands, Milton et al. (1994) present a conceptual model of arid rangeland degradation that suggests that degradation proceeds in steps-increasingly difficult and costly to reverse-and discusses adaptation options (see Box 2-4). Assisted management is a lot harder for wildlife in game reserves than for livestock. Monitoring is required to identify populations at risk (from deforestation), as well as reserved areas that are changing their vegetation types in response to climate, leaving some animals in habitat types that are not suitable. Massive fragmentation of previous forests and woodlands makes it difficult for wildlife to migrate along corridors to areas with more water and foliage. Close monitoring would identify groups of wildlife that are in danger, and steps can be taken to move them to suitable habitat.

At the institutional level, mechanisms need to be created (or improved upon) to facilitate the flow of scientific results into the decision-making and policy-making process. Joint planning of projects that would impact cross-boundary catchment areas will become increasingly important if the climate becomes more variable and water more scarce for many regions of Africa.

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