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Sensitivity analyses of major rivers of the continent indicate that these rivers are sensitive to climate change. Magadza (1996) examined changes in water storage in Zimbabwe's main water storage facilities during the 1991-1992 drought cycle. During this period, the mean temperature averaged 2°C above the long-term seasonal mean, and seasonal Penman evaporation exceeded the long-term seasonal mean by more than 30%—peaking at just less than 90% in February at the Kutsaga station. During this drought cycle, stored water resources dwindled to less than 10% of installed capacity.
Urbiztondo (1992) simulated the response of Lake Kariba power-generating capacity to various climate change scenarios. His results indicate that with no significant change in precipitation, the lake would regulary fail to meet installed generating capacity if the temperature rose by 4°C. During dry years, generating capacity would decrease by as much as 50%. Even during wet years, maximum generating capacity would barely exceed 50% of installed capacity.
Economic impacts from curtailment of hydropower generation from Lale Kariba, as a result of the 1991-1992 drought, were estimated to be US$102 million loss in GDP, US$36 million loss in export earnings, and loss of 3,000 jobs (Benson and Clay, 1998). The direct impacts on agriculture and the knockon impacts also were quite severe. These limited estimates provide a window on potential economic impacts of climate change-mediated water resources changes in the medium term (i.e., into the middle of the 21st century—a time span within the planning window of economic development strategies).
With an estimated error of about 8%, the Gambia River flow has been shown to be very sensive to climate change. Based on the results of river flow responses and vulnerability analysis, climate variables alone can cause a 50% change in runoff in the Gambia River catchment (Jallow et al., 1999). In general, a 1% change in rainfall will result in a 3% change in runoff (Manneh, 1997). On the whole, this translates into saltwater intrusion into the Gambia River by 40 km at times of maximum intrusion. However, the flushing action of freshwater flow of the river will keep the saline/freshwater interface at an equilibrium, oscillating between 90 and 290 km. The rate of saline water intrusion during dry seasons would increase from about 20 km per month in January to about 40 km per month in April and May.
Likely changes in precipitation and discharge regimes call for a wide range of adaptations. Broadly, these adaptations would include:
Although there are now subregional climate change scenarios for the African region, the quality of such scenarios varies with the intensity of historical data and the spatial distribution of monitoring stations. There is an urgent need to intensify the density of monitoring stations to improve climate change scenarios. The cost of rehabilitating stations that are in disrepair is not beyond the financial capability of African states. Appreciation of the strategic importance of these facilities and a sense of ownership of climate change concerns needs to be reawakened.
It has been noted that practically all of the major river basins of Africa include several states. In recognition of this fact, the past decade has seen the development of international river basin mangement protocols—such as the Southern Africa Development Community (SADC) Protocol on Shared Waters, the Niger Basin Authority, and several others, including the more recent Lake Victoria Fisheries Authority. The United Nations Environment Programme International Environmental Technology Center (UNEP-ITEC) have emphasized the river basin as the fundamental unit of management (UNEP, 2000). We recommend that these international basin authorities be strengthened in terms of finance and human resources and that their perspectives should embrace near- and long-term climate variability and climate change issues in their work plans. Most important is that the legal framework for such river basin authorities should be robust to ensure equity in access to and accountability for water supply and water quality management. Failure to take these concepts on board could lead to water resources-related conflict.
In general, the African continent lacks technical strategies to optimize water resources. A few countries (e.g., South Africa and Zimbabwe) have begun to develop strategies for optimum use of water resources—using, for example, water pricing and demand management tools. Crop-watering technology is primitive and wasteful in most cases. Few industrial and household water-usage strategies incorporate water reuse. During drought periods, management authorities have resorted to supply restrictions, such as the 3-day supply per week in Mutare during the 1991-1992 drought. Water supply shortages conventionally are addressed through construction of more impoundments. Magadza (1996) remarks that in severe drought periods there would be a multiple failure syndrome of water storage facilities, especially where individual reservoirs are dedicated to defined communities. Although supply structures (banning of garden hoses) and construction of storage reservoirs are practical options, demand management—which reduces consumption per unit of product output—has proved increasingly to be a water-saving strategy that can allow communities to enter a drought cycle with adequate supplies.
Whatever strategies are adopted for optimizing water usage, successful development of such strategies is contingent on reliable meteorological and hydrological information. In many instances, application of hydrological models on a basin-wide scale is restricted by data density. Reliable impacts assessments and near-term predictions depend on robust databases. For example, flood propagation and thus flood warning capability, which are real-time processes, are a function of the density of measuring points. Similarly, crop yield forecasts could be made spatially more accurate by improving the intensity of climatic measurements.
Over the past half-century, Africa has invested heavily in hydroelectric power schemes. Recent drought episodes and demand escalation have highlighted the vulnerability of even the largest hydroelectric plants to climate variability (Magadza, 1996). This assessment has shown that future water resources, especially in the subhumid to semi-arid regions of the African savanna and subtropics, will be more restricted. Research into other forms of renewable energy and energy-use efficiency in industry and households is an essential inverstment in a more energy-secure future. At the regional level, energy resource sharing is a necessary strategy. Individual states must have trust and confidence to invest in neighboring countries for overall regional energy security.
Populations that live in flood-prone areas need to consider strategies for early warning procedures for flood events; strategic planning in the location of human habitations to minimize flood impacts; and strategies for robust protocols for alleviating impacts of drought events to minimize loss of human life, economic assets, and societal norms. On the other hand, early warning systems can be effective if impacted areas are accessible in the worst-case scenario, to enable either evacuation or relief supplies delivery.
Although there are major reservoirs on most large African river basins, these reservoirs were not designed for flood control. However, synchronization of operations of reservoirs that are located in the same basin can alleviate flood impacts. Nevertheless, there is a need to consider purposely building flood control facilities in some of the flood-prone areas of Africa, similar to those found on the Danube, which reduce flood crest intensity by sequestering floodwaters into temporary storage facilities along the river. This could be a subject of directed research for each African basin.
Research into coastal defense systems is an immediate need. Several African coastal areas already are experiencing sigificant coastal impacts. Coastal management infrastructures are likely to entail intergenerational investment programs in which each extent generation must make its contribution to minimize long-term costs. If our generation abrogates our responsibilities to future generations, we will impose immense costs on our posterity.
To minimize sensitivity to climate change, African economies should be more diversified, and agricultural technology should optimize water usage through efficient irrigation and crop development. Considerable advances have been made in agricultural industries of southern Africa, particularly in South Africa and Zimbabwe.
As water resource stresses become acute in future water-deficit areas of Africa as a result of a combination of climate impacts and escalating human demand, there will be intensifying conflict between human and environmental demands on water resources. Because maintanance of healthy ecosystems is an underpinning to economic sustainability, there is need in each water basin management unit to identify and factor into development projects the need for environmental flows.
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