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Rodger L. Mpande, Commutech
Michael Tawanda, Population Studies Program, University of Zimbabwe
Continuing human population growth, and the attendant increased demand for freshwater, are leading inexorably to what may be called a world water crisis. In a microcosm, this growing competition is nowhere exemplified more graphically than in the Southern African Development Community (SADC), a region encompassing 12 countries, including Angola, Botswana, Lesotho, Malawi, Mauritius, Mozambique, Namibia, South Africa, Swaziland, Tanzania, Zambia, and Zimbabwe. Seven of the principal river basins of Southern Africa the Zaire, Zambezi, Okavango, Limpopo, Orange, Ruvuma, and Cunene, with a total catchment area of 6.76 million square kilometers (km2) are shared by at least two of the 11 countries (Mauritius is excluded).
Drainage Area and Riparian Countries
Of the basins in Southern Africa, the Zambezi Basin, shared by Angola, Botswana, Malawi, Mozambique, Namibia, Tanzania, Zambia, and Zimbabwe, has become the subject of much interest in recent years (Table 1).
Rising in northwestern Zambia, the Zambezi Basin runs for approximately 3,000 kilometers to the Indian Ocean, en route providing a drainage basin of about 1,400,000 km2 (Pinay, 1988). Much of the basins waters are used to generate hydroelectric power (HEP) primarily from the two largest human-made lakes, Kariba, 5,250 km2 holding 156 cubic kilometers (km3); and Cabora Basa, 2,739 km2 holding 56 km3. Both lakes are located on the Zambezi Basin and serve Zambia and Zimbabwe, and Mozambique and Zimbabwe, respectively. Itezhitezhi (365 km2) and Kafue Gorge (180 km2) also provide for HEP generation. These artificial impoundmentís have also facilitated the development of other uses of the basinís waters, such as for recreation and fisheries.
The regionís rainy season stretches from October/November to March/April, with the amount of rainfall generally increasing from southwest to northeast. However, no area receives more than 1,600 millimeters (mm) of rain per rainy season. The distribution of rainfall is also erratic, with recurrent drought becoming a characteristic feature of the area. In recent times, droughts have occurred in 1946-47, 1965-66, 1972-73, 1982-83, 1986-87, 1991-92, 1992-1993, and 1993-94. In fact, localities that receive 400-600 mm of rain can expect to experience six droughts lasting two or more years every 50 years (Rukuni, 1995). These areas include southern Angola, most of Namibia and Botswana, southern and western Zimbabwe, southwestern Zambia, and northern South Africa.
More recently, the rising human population has combined with the food and water shortages and high livestock mortality occasioned by recurrent drought to increase both the demand for the waters of the Zambezi and the potential for competition among agricultural, domestic, and industrial uses. In view of these developments, managing this trans-boundary river basin will be critical to ensuring the future water supply for the region as a whole and for individual countries.
Population Growth and the Increasing Need for Irrigation
Current trends in population growth offer a bleak prognosis for meeting the escalating demand for water. Total Fertility Rates (TFRs), the average number of children a woman bears in her lifetime at the current birth rate, ranged from 4.1 in South Africa to 6.7 in Malawi in 1995, for a regional average of 5.6 (Table 2). However, the average Crude Death Rate (CDR), the number of deaths per 1,000 of the population, was estimated at 2.7 for the same period (Population Reference Bureau, 1995). This combination of high fertility with low mortality has generated an average annual population growth rate of three percent in the region, for the period 1990-1995.
At current rates of growth, the population in the community is expected to increase from approximately 137 to 197 million persons between 1995 and the year 2010. On average, these countries are also expected to double their populations within 27 years.
One immediate consequence of rapid population growth is an escalation in the demand for agricultural products. For the members of SADC, and given that reduced availability of arable land is a corollary of population increase, meeting this need may be achieved through intensification, rather than extensification of farming. Members of SADC should focus their efforts on expanding the area of land under irrigation, with water sourced from the Zambezi Basin and its tributaries. As shown in Table 3, in all the four countries for which data are available, only Zimbabwe is currently irrigating more than one percent of the land available for irrigation.
For individual countries, the total land available for irrigation is, however, only a theoretical maximum. The amount of water that each country will actually need depends upon location as well as on crop type. Production of one ton of cereal, for example, requires between 500-2,000 tons of water, a requirement that is not easily achieved. As shown in Table 4, if any one of either Zimbabwe, Botswana, South Africa, or Namibia adopts a long-range, strategic perspective regarding its water supplies, these countries will be competing for regional waters within the next 25 years. Furthermore, an increase of 25,000 irrigated hectares in one of the basin states would translate into water requirements that are above the minimum recorded flow of the Zambezi.
The potential for intra-regional conflict over scarce water is also exacerbated by the lack of complete efficiency in the irrigation process itself. It has been noted that, before reaching the land under irrigation, between 40 percent and 60 percent of the water drawn from rivers and dams is lost through seepage and evaporation (Tolba and El-Kholy, 1992).
High urban growth rates are also increasing the demand for water for domestic consumption, power generation, industrial uses, and mining. In the period 1990-1995, average annual urban growth rates in the region ranged from 3.17 percent for South Africa to 7.08 percent for Mozambique, for a regional average of 5.27 percent (Table 5). This figure, 5.27 percent, is slightly more than double the corresponding world rate of 2.63 percent; it is roughly about 1.5 times the average for less developed countries as a whole. It is also estimated that in the period 2005-2010 average annual urban growth rates will range from 3.10 percent for South Africa to 5.88 for Malawi, for a regional average of 4.58 percent. While these figures suggest declining rates of urban growth, the disparity between the rates for the region, less developed countries, and the world will continue.
Current basin-wide data on migration is not available. However, preliminary results of intercensal urban growth (1982-1992) undertaken by the Zimbabwe Central Statistical Office suggest an average growth rate of 40 percent as the total effective contribution of migration to the growth of cities and towns in that country. Additional results from the same study also indicate negative net rural and positive net urban migration across all ages. On the basis of these results, and at least for Zimbabwe, it appears that rural-urban migration, partly in response to the effects of drought, is a major factor in urban growth. On the basis of these preliminary results, the contribution of the rate of natural increase to urban growth exceeds that of migration.
In the case of Mozambique and Angola, the dynamics underlying their high rates of urban growth are somewhat different. Protracted civil war in these two countries has made their rural areas virtually unlivable for the civilian population, thereby engendering massive rural-urban migration flows.
As a consequence of the urban dynamics in the region, approximately 40 percent of the population in the SADC were living in urban areas in 1995, a figure which is projected to increase to slightly more than 43 percent by the year 2010 (Table 5). It should be noted, however, that the latter figure obscures wide intra-regional variation. While the level of urbanization in Malawi is projected to be as low as 21 percent by the year 2010, urbanization levels in Angola, Botswana, Mozambique, South Africa, Swaziland, and Zambia are all expected to exceed 44 percent. In addition, as early as 1990, a number of the regionís urban centers already had populations that were either close to or in excess of one million in number (UN, 1993). These urban agglomerations included Luanda in Angola (1.6 million); Maputo in Mozambique (1.6 million); Lusaka in Zambia (1.0); Harare in Zimbabwe (0.9 million); and Cape Town in South Africa (2.3 million).
Large and increasing populations in general and growing urban populations in particular, exacerbated by the effects of drought, mean that water shortages may soon become a characteristic feature of the SADC regional landscape. Consequently, within the next 25 years, and in response to population growth, domestic and municipal water usage will increase significantly, putting even more pressure on the need to withdraw water from the Zambezi River.
According to the World Health Organization, human beings need about five liters of water each day for cooking and drinking. However, good health and cleanliness require a daily supply of about 30 liters per person, or about 11 cubic meters (m3) per person per year. In Africa, per capita withdrawals for domestic and municipal use are currently estimated at only 17 m3 per year (in contrast, the figure for North Central America is 167 m3 per year.). However, some of this amount is often simply wasted or lost through leakages. For example, following the disruption of normal water supplies in June 1995, hundreds of residents of Harare, the capital city of Zimbabwe, had to spend days queuing for water (Sunday Mail, 1995).
Urbanization is usually associated with some level of industrialization, and, like most other human activities, industrial production is dependent on water for processing, cooling, and waste management. Current per capita water withdrawals for industrial usage are estimated at 12 m3 per year in Africa. The demand for water in some of the major urban-industrial centers in the Zambezi River Basin, however, already far exceed the capacity.
More specifically, Botswana, Namibia, and Zimbabwe are expected to face a major water shortfall in the industrial sector by the year 2020. It is also projected that South Africa, with one of the fastest growing industrial sectors in the region, will run short of water in the first half of the next century. As a case in point, while the mean annual run-off of the Zambezi River at Cabora Basa is roughly 88 x 10 m3, the current total demand in South Africa is approximately 20 x 10 m3 per year.
In Bulawayo, the second largest city in Zimbabwe, water use for industrial purposes currently consumes 37 percent of the cityís total. This figure is expected to increase proportionate to growth in that sector. The heavy competition between Bulawayo and the neighboring farming community, which uses underground water for agricultural purposes, is illustrative of the problems that will have to be faced in the future as industry grows in the major urban centers.
To support its industrial needs, Bulawayo now draws at least 25,000 m3 of water per day from an aquifer 40 kilometers north of the city. Of concern, however, is the fact that these withdrawals are being undertaken without adequate data on the extent and capacity of the aquifer, the water recharge levels, and estimates of quantities of water being used by the farmers. Under these circumstances, the possibility of the aquifer drying up cannot be ruled out. A recent consultantís evaluation estimates that at the current levels of withdrawal by the Bulawayo City Council, the aquifer may be drawn down to levels that will not sustain current farming activities.
Power generation, one of the major commercial uses of the waters of the Zambezi Basin, is an additional source of competition for scarce water. A total capacity of 4,511 megawatts has been developed in the basin at present, representing approximately 36 percent of the total, commercially viable HEP potential. However, as greater use is made of water flowing into the Zambezi for domestic, municipal, and agricultural purposes, less water will be available at large dams such as Kariba and Cabora Basa.
The competing demands for water for hydropower generation and other uses has generated debate over the economic value of water. While HEP is a non-consumptive use of water, reservoirs may experience large losses from evaporation and seepage. It is estimated, for example, that the evaporation loss of Kariba is equivalent to 20 percent of the flow of the Zambezi at Victoria Falls (Manley, 1995). In contrast, a case study undertaken in Botswana revealed that the long-term run marginal costs for urban and village water are generally ten to 100 times larger than the value of water used for hydroelectric purposes. What is important, therefore, is that the Basin states balance hydropower projects with other water development infrastructure in order to satisfy the economic and human needs of the region.
Of major threat to the Zambezi Basin is pollution from industrial and domestic sewage effluent from the main urban centers in the region: Livingstone (population, 100,000); Victoria Falls (25,000); Kariba (30,000); and Siavonga (20,000). Other growing population centers are Binga, Kabane, Katima Mulilo, and Chirundu. Further from the river but within the Zambezi Basin are large cities, including Lusaka and Harare. In the case of Livingstone, liquid waste from several population centers is discharged untreated into the Zambezi. As a large flowing river, the Zambezi can purify itself. However, as the number of dams increases, creating standing waters, the situation may change. Effluent collecting in the reservoirs may lead to eutrophication problems.
The effects of pollution are already evident. As shown in Table 6, the percentage of the population in both rural and urban areas in the region who have access to safe water is less than 100 percent in all countries, except Botswana. In urban areas in particular, spontaneous settlement the consequence of rural-urban migration due to drought or conflict or both and the inadequacies of the urban management system mean that many are without adequate sewage and refuse disposal services. The resultant waste may then contaminate the available water supply by seeping into feeder streams.
The environment is another major source of water use that, nevertheless, does not usually appear in consumption statistics. While wildlife, wetlands, lakes, rivers, and other ecosystems need water to survive, dams decrease water flow, thereby preventing the annual flooding required by the flood plain ecosystems at places such as Mana Pools, and Marromew on the Zambezi.
The diverse ecosystem of the Zambezi River Basin also provides a wide range of natural resources that support the local population. More specifically, forestry, wildlife, fisheries, and related tourist attractions are a source of livelihood for many. Several national parks, game reserves, and safari areas are also located within the basin. They include Kameha (Angola); Chobe National Park (Botswana); Chobe and Kasane Forests Reserves (Botswana); Caprivi Game Reserve (Namibia); all the parks and game reserves of Zambia and Malawi; the major part of the parks and wildlife estate of Zimbabwe, and some parks in Mozambique. These estates provide a habitat for arguably the largest variety of bird and animal species in the world. All the popular tourist activities, including game viewing, sightseeing, sport fishing, white-water rafting, canoeing, and photographic and hunting safaris, require that the Zambezi Basin retains its wilderness aura and continues to offer a suitable habitat for its game.
The basin also supports subsistence, artisan, and commercial fisheries. These fisheries depend upon the availability of relatively nutrient-rich water.
A number of national and regional water resource plans exist in the basin, including those for inter-basin water transfers to the non-riparian member states of SADC. However, neither these plans nor existing development have been integrated into one basin-wide water resource management plan. The governments of Botswana, Zimbabwe, and South Africa, for example, have all contemplated drawing water from the Zambezi River. These proposals have not, however, been examined for regional socioeconomic merits and environmental consequences. Other areas of concern include the technical, legal, environmental, socioeconomic, and institutional effects of the proposals on the region.
The lack of integrated plans has been recognized as one of the major constraints in promoting sustainable development and equitable sharing of water resources in the shared water course systems in the SADC. This fact further limits socioeconomic growth and environmentally sound management associated with water resource development in riparian countries. In the final analysis, the efficient operation and management of water resources development, and the equitable sharing and utilization of their benefits, are only marginally realized in the absence of such a comprehensive, integrated, basin-wide approach in the development and management process.
This chapter has emphasized that rapid population and urban growth rates, exacerbated by recurrent drought, set the stage for increased competition for the waters of the Zambezi River Basin. To ameliorate this outcome, the authors recommend that the following six measures be implemented:
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