Climate Change and Freshwater Resources
Water is needed in all aspects of life. The general objective is to make certain that adequate supplies of water of good quality are maintained for the entire population of this planet, while preserving the hydrological, biological and chemical functions of ecosystems, adapting human activities within the capacity limits of nature and combating vectors of water-related diseases. "Agenda 21 - United Nations 1992"
Water is an issue that cuts across many thematic sectors such as agriculture, energy, human settlements, livelihoods, tourism, health, industry, recreation, wildlife, forest, etc. Water is a priority resource, and as such there is a need to understand its actual and potential sustainability from a regional and local perspective in the context of the watershed as the system of analysis. Small changes in the ecological system may have significant and dynamic responses on water quality, quantity and distribution. Furthermore evapo-transpiration, one of the key variables in the hydrologic process is the link that balances the equations between the global hydrological and energy cycles.
Climate change will have both adverse and beneficial impacts on natural and socio-economic sectors. The biological and economic productivity will decrease for some sectors, but increase for others. Natural resource sectors and biological diversity could in extreme cases be severely affected, reduced or depleted (CICERO). In developing countries whose economies often to large extent rely on climate sensitive sectors, adverse climate change impacts could inflict damage to the national economy. Africa is believed to be the continent most vulnerable to the impacts of projected changes in the climate. While the link between extreme events and global climate change is uncertain, the increasing frequency and severity of extreme events is likely to have far reaching consequences for the people and ecosystems in Africa. People dependent on river basins and wetlands face losses of freshwater biodiversity and a reduction in ecosystem services including water supply, water purification, and flood control. People dependent on fuel wood face increasing energy poverty and insecurity.
What is Climate Change? How vulnerable are Global Water Resources?
While there is presently little certainty about the form that global climate changes will take, there is little doubt that climate change will alter the global hydrological cycle in a variety of ways. At the most general level it has been predicted that: Warmer temperatures will lead to a more vigorous hydrological cycle; this translates into prospects for more severe droughts and/or floods in some places and less severe droughts and/or floods in other places (IPCC 1996). Several models indicate an increase in precipitation intensity, suggesting a possibility for more extreme rainfall events. They suggest that downpours will become more intense which will increase floods and runoff while reducing the ability of water to infiltrate the soil. Changes in seasonal patterns may affect the regional distribution of both ground and surface water supplies. While changes at the surface would influence the recharging of groundwater supplies and, in the longer term, aquifers. Water quality may also respond to changes in the amount and timing of precipitation. (IPCC 1997). Freshwater ecosystems will respond to altered flood regimes and water levels. Changes in water temperatures and in the thermal structure of fresh waters could affect the survival and growth of certain organisms, and the diversity and productivity of ecosystems. Changes in runoff, groundwater flows, and precipitation directly over lakes and streams would affect nutrients and dissolved organic oxygen, and therefore the quality and clarity of the water. (IUC)
Effects of Climate Change on Water Resources
Source: Lasse Ringius, Thomas E. Downing, Mike Hulme, Dominic Waughray and Rolf Selrod Center for International Climate and Environmental Climate Change in Africa - Issues and Challenges in Agriculture and Water for Sustainable Development Report 1996:8
How vulnerable are Southern Africas Water Resources?
The Southern African region comprises various natural environments and has a variety of tropical and temperate zones. The mostly arid and semi arid regions are characterised by a large availability in the annual mean rainfall. Regional estimates put renewable freshwater resources at an annual average of 650 billion m3, which is distributed amongst rivers, lakes and groundwater bodies throughout the region (SADC 1998) The average annual rainfall varies across the region, from more than 1 500mm in the northern and north-eastern parts, to less than 25 mm in the very arid Namib Desert in the south-west (DRFN), leaving some areas with abundance of water and others a scarcity.
Over the past 20 years there has been noticeably less rainfall in Southern Africa with 1991/92 and 1 994/95 wet seasons being of the 5 driest this century. (WWF Climate Change in Southern Africa, 1998) The 1991/92 drought in Southern Africa put between 18 to 20 million people at risk of starvation. (Zero 1996,WWF, 1998) Authorities estimated that more than 5 million Zimbabweans and half the countrys population, faced, hunger due to large crop failure form the 94/95 drought, and the worst experienced in the region history Lakes such as Victoria, Malawi and Tanganyika are in delicate hydrological balance small changes in the temperatures and rainfall could result in lower lakes levels (Arnell et all, 1996), Lake Victoria has dried out completely in past eras (130).
At the same time, floods from occasional torrential rains have in some areas brought about extensive damage to property and death to people and animals. After the 1994/1995 drought, large floods occurred in the Limpopo and Incomati Rivers in 1996. In the same year the Pungue River also experienced devastating floods. (SADC pg4). Historical flooding event documentation indicated that flooding on a national levels is fairly frequent, with the occurrence of significantly damaging floods in South Africa is on average between once and twice a year.
A WWF study Climate Change and Southern Africa, commissioned by WWF and coordinated by Dr. Mike Hulme of the Climate Research Unit (CRU), at the University of East Anglia, UK assessed the impact of Climate Changes based on Intergovernmental Panel on Climate Change (IPCC) methodologies. Three alternative climate change scenarios, "core," "dry," and "wet" were assessed. All three scenarios are based on a temperature rise of 1.7░ C by the 2050s decade. This is agreed by the IPCC scientists to be the most likely amount of warming assuming little or no action is taken to reduce greenhouse gas emissions (without taking into account the slight moderating effect of aerosols in the atmosphere). The "core" scenario points to modest drying over large parts of the region, plus widespread increases in rainfall variability. In Zimbabwe, this scenario would result in around a 5% decrease in annual rainfall, and this in turn would translate into agricultural problems, with yield reliability for the staple maize crop declining. Changes in surface water availability would reduce farmers' ability to use irrigation in compensation for poor rainfall. The "dry" scenario shows that rainfall could decline by as much as 10% across the region, while under the "wet" scenario most of the region gets wetter.
Four effects of global change are of primary importance to Southern Africa;
changes in river runoff, changes in groundwater recharge, changes in water availability and rises in sea levels. The severity of these changes will depend on the effects of increased CO2 concentrations, altered precipitation and soil moisture, and increased temperatures. CO2 concentrations will probably increase to 459-550ppmv by 2050, compared to about 350 at present. CO2 enrichment in the atmosphere is likely to reduce the rate at which plants transpire, resulting in an increase in water use efficiency, although the extent to which this enhances water catchment yields is uncertain (Cicero). Increased temperatures increase the atmospheric demand for water, both evaporation from soils and open water and transpiration from plants. The extent to which precipitation offsets the increased evapotranspiration demand is highly uncertain in Africa. According to the IPCC, a reduction in precipitation projected by some GCMs for the Sahel and southern Africa, if accompanied by high inter-annual variability, could be detrimental to the hydrological balance of the continent and disrupt various water-dependent socio-economic activities. It is likely that some regions will suffer significant decreases in moisture availability, even when the direct effects of CO2 enrichment are included. The risk of drought is likely to increase in such regions as well.
Climate change, Evaporation, Runoff
Runoff in southern Africa spans a great range, from less than 10mm to over 700mm. Interannual variability is greatest in the semi-arid regions (for example, runoff in southern Zimbabwe between 1961 and 1990 varied almost 0 to over 150). South Africa has close to the lowest conversion of rainfall to usable runoff from rivers of all countries in the world. Of the rain that does fall, about of half is caught and stored in dams, while about 8% returns to the sea in rivers and the rest disappears as evaporation, evapotranspiration and infiltration into the ground (Davies and Day 1998). The 1400km of the orange river to the Vanderkloof Dam to the river mouth flows through some of the hottest and most arid regions in the world, and is subject to net evaporation rates of up to 3 metres per annum (Mckensi and Craig). The evaporation at Kariba is 20% of flow of the Zambezi at Victoria Falls (112), The average inflow to Pequenos Libombos, Maputos main reservoir is 7 cm/s, while the average evaporation rates are estimates at 2 cum/s. (SARDC). In 1998, the Namibian Legal Assistance Center estimated that the amount of water lost annually through evaporation at Epupa would be equivalent to the amount of water, which could supply the needs of the entire city of Windhoek for 42 years.
Southern Africa experiences very high losses of water from evaporation and transpiration, with the result that only a very small proportion of the total rainfall enters the streams or groundwater, where it is available for human consumption. On average 65% of all the rainfall in the region evaporates soon after it has fallen. This value is much lower in relatively cooler and more humid areas in the region, but can get as high as 83% in Namibia, the regions driest country. The increased temperatures will likely lead to increase open water and soil/plant evaporation. Exactly how large this increased evaporative loss will depends on factors such as physiological changes in plant biology, atmospheric circulation and land use patterns. As a rough estimated potential evaporation over Africa may increase by between 5% and 10%.( Cicero 1996)
Relatively small changes in temperature and/or rainfall can have significant effects on evapotranspiration and groundwater recharge. These changes will impact both the total annual flow in rivers and its distribution through the year. In a dry area of Tanzania model results indicate a dramatic 40% decrease in recharge caused by a 15% reduction in annual rainfall, which is further accentuated under degraded conditions to a 58% decrease (Sandstr÷m, 1998). Since dry season flow in rivers is maintained by groundwater recharge this has severe implications for freshwater ecosystem integrity in this and similar areas. Reynard and Andrews (1995, see also Hulme 1996) predict an overall reduction in annual rainfall in southern Africa and a change in the inter-annual variability of runoff. Model scenarios for 2050, following the standard IPCC methodology (Carter et al. 1994), indicate that runoff would decrease in two of the scenarios (UKTR and CCC) across most of the region. However, runoff increases in the "wet" scenarios, based on the OSU GCM experiment. For the drier scenario, decreases of 10-40% are widespread. With climate change, the variability of runoff increases for the UKTR scenario, which included GCM results on the interannual variability of rainfall
The IPCC response strategies recommended that increased runoff due to climate change could potentially pose a sever threat to the safety of existing dams with design deficiencies. Design criteria for dams may require re-evaluation to incorporate the effects of climate change.
Climate Change and Irrigation
Currently, there is a strong attraction toward the development of irrigation projects in the region. This is largely the result of the growing incapacity of the region to feed itself (as a result of land degradation and recurrent droughts), as well as the desire of governments in southern Africa to generate foreign currency through the export of cash crops such as tobacco. Irrigation projects are most developed in Zimbabwe (130,000 hectares), Tanzania (25,000 hectares), and Malawi (19,000 hectares). The main irrigated crops are wheat, cotton, maize, tea, and sugar. The irrigation potential is interwoven into the socioeconomic fabric of the southern African states. It, therefore, becomes imperative to study present and future trends associated with irrigation practices, that is, the depletion of surface and underground water. In addition, irrigation of large tracts of land may lead to the uprooting of local people from their traditional lands in addition to adverse environmental impacts of reservoir development, including downstream effects. Some studies on the effects of anthropogenically induced climatic changes on irrigation water consumption were conducted by the Food and Agriculture Organization (FAO), along with the UK's Institute of Hydrology, for the Malibamatsama Basin, 3,240 km 2 in Lesotho (Nemec, 1989; Institute of Hydrology, 1988). Future climate change simulations for this region have been accomplished using a general circulation model with a doubling of CO2. The model's output indicated a 6 degree C increase in mean monthly temperature, a 4-23% decrease in monthly precipitation from December to May, and a 10-15 % increase in monthly precipitation from June to November. This research suggested that with a doubling of CO2, changes in meteorological conditions in the basin would lead to a 65 % increase in water demands for irrigation, bringing about the shrinkage of irrigated areas from 37,500 ha at present to 20,000 ha.
Studies of climate impacts related to agriculture should also examine the likely effects of climate change and variability on the irrigation potential of southern Africa. Such a study would provide useful indicators of possible future changes in the region's water balance.
Climate Change and Water Health
Climatic changes will create the preferred conditions for disease-carrying mosquitoes and parasites (tsetse flies and ticks). Diseases that thrive in warmer climates such a malaria, cholera and yellow fever are likely to spread, By 2100 it is estimated that there could be an additional 50-80 million cases of malaria each year.
These warnings should be particularly relevant for the dam building industry. Since the construction of major dams on the Vaal and Orange Rivers, which have eliminated the natural seasonal rise and fall of water levels in these rivers, the occurrence of blackfly has escalated. Blackflies are major pests of livestock and labour intensive farming along several rivers in South Africa; along the Orange River in particular along the Vaal, Great Fish, Sundays and Gamtoos. Blackflies along the middle and lower Orange River are estimated to account for a loss of approximately R 88 million per annum, in lost animal production (WRC) 1998. Similarly, the IPCC has suggested that a drop in water level in dams and rivers could adversely affect the quality of water by increasing the concentrations of sewage waste and industrial effluents, thereby increasing the potential for the outbreak of diseases and reducing the quality and quantity of fresh water available for domestic use.
Water Stress in Southern Africa
It is likely to add to economic and political tensions, particularly in regions that already have scarce water resources. Of the 19 countries around the world currently classified as water-stressed, more are in Africa than in any other region, and this number is likely to increase, independent of climate change, as a result of increases in demand resulting from population growth, degradation of watersheds caused by land use change and siltation of river basins.(IPCC) At present, approximately one third of the world s population live in countries experiencing water stress. It has been forecast that by 2025 as much as two thirds of a much larger world population could be exposed to water stress, simply due to the increase in population. Water resource stresses in many of the poorest countries, already expected to increase, will be exacerbated by climate change. Due to climate change alone, some 66 million extra people will live in countries with water stress and some 170 million people will live in countries, which are extremely stressed (Hadley Centre 1998). Current calculations are that by 2000, South Africa will suffer water stress, Malawi will have move into absolute water scarcity and Kenya will be facing the prospect of living beyond the present water barrier. By 2025, Mozambique, Tanzania and Zimbabwe will suffer water stress, Lesotho and South Africa will have moved into absolute water scarcity and Malawi will have joined Kenya living beyond the present water barrier [ADB Harare, 1994 p39]. It is estimated that all of Southern Africas fresh water resources would be fully used between 2025 and 2030, according to the Orange River Replanning Study (ORRS), an undertaking of the South African Department of Water Affairs and Forestry (DWAF). The interaction between population growth and finite water supply means that water availability per capita will decrease (Falkenmark, 1989:113)
Although it is too early to say which of these scenarios is most likely to materialize, the prospect of such climate change means that the region needs to prepare itself for some substantial changes in weather, particularly in the timing and distribution of rains. These changes will alter natural vegetation, wildlife habitats, crop growing seasons, and the distribution of pests and diseases. Much greater adaptability will be required in the future on the part of farmers, rural communities and government agencies in hard hit parts of the region.
Human induced climate change is no longer a theoretical concept It is real. It is an issue that will affect all human and ecological systems and socio-economic development. In spite of current international initiatives and country mitigation measures, climate change is inevitable. The implications of climate change for water systems managers are complicated by the spatial coarseness of climate change predictions, differences between regional and district level management of water resources, and the predicted decline in water availability facing water supply systems due to other factors over the next fifty years. Adaptation, particularly, in the water and energy sectors, along with mitigation, must be considered urgently as part of a integrated regional response to climate vulnerability and change. Preparing for climatic hazards will require reducing vulnerability, improving the efficiency of water use, developing monitoring capabilities and contingency plans, and utilizing climatic forecasts. New supplies must be developed and existing supplies used more efficiently. Long-term management strategies should include: regulations and technologies for directly controlling land and water use, incentives and taxes for indirectly affecting behavior, the construction of new reservoirs and pipelines to boost supplies, and improvements in water-management operations and institutions. Other adaptation measures can include removing levees to maintain flood plains, protecting waterside vegetation, restoring river channels to their natural form, and reducing water pollution. [See Table 2] Enhanced preparedness is thus a direct response to climate change as well as contributing to current development objectives
Adaptation is now widely appreciated to be a dynamic process and not a one step response to a single impact.Water Resources Vulnerability
South Africas rainfall is erratic in distribution and variable between years. Most of the country is arid and subject to droughts and floods. South Africas industrial, domestic and agricultural users are highly dependent on a reliable supply of water. Since water-supply infrastructure takes years to develop and is designed to last for decades, water resource planners need to consider the possibility of climate change. Even without climate change, South Africa is predicted to have exhausted its surface water resources early in the 21st century. A reduction in rainfall amount or reliability, or an increase in evaporation (due to higher temperatures) would exacerbate this situation.
The most critical factor associated with climate change impact is the availability of water resources. Changes in seasonal distribution and intensity of precipitation impact on soil water storage, runoff processes and groundwater recharge, whilst temperature changes are an important factor in potential evaporation. Increased temperatures will increase the atmospheric demand for water, evaporation from soils and open water, as well as transpiration rates from plants. The extent to which precipitation change will offset the increased evapo-transpiration rate is uncertain.
The arid and semi-arid regions, which cover nearly half of South Africa are particularly sensitive to changes in precipitation because the fraction of rainfall that is converted to runoff or percolation to groundwater is small (Schulze, 1997a). Equally important consequences of global warming are the potential changes in the intensity and seasonality of rainfall. Increased convective activity could increase the frequency and intensity of rainfall events, augmenting runoff volumes and potentially causing higher soil losses (Schulze, 1997b).
While some regions may receive more surface water flow, water scarcity, increased demand and water quality deterioration are very likely to be problems in the future with or without climate change (Ringius et al., 1996). However, climate change may alter the magnitude, timing and distribution of storms that produce flood events. The areas most sensitive to a change in precipitation are in the winter rainfall region. A small change in precipitation will have a large effect on water runoff because evaporative transpiration rates are low in the winter and soil moisture conditions often remain high between rainfall events. Consequently, a higher rate of runoff is expected. However, should the temperature increase by 2oC, the evaporation rate in the south-western Cape will increase and runoff may reduce by 10 percent by the year 2015.Adaptation
A number of adaptation options have been identified.
Monitoring and forecasting systems for flood and droughts should be improved.
Significant Water Resource Strategies to Adapt to Climate Change in Africa
Sources: see Benioff (1996), Riebsame (1995), Kaczmarek and Napiorkowski (1996), Golubtsov et al. (1996), Campos et al. (1996), Smith and Lenart (1996), Stakhiv (1996).Agenda 2: Chapter 18 PROTECTION OF THE QUALITY AND SUPPLY OF FRESHWATER RESOURCES: APPLICATION OF INTEGRATED APPROACHES TO THE DEVELOPMENT, MANAGEMENT AND USE OF WATER RESOURCES Impacts of Climate Change on Water Resources Basis for Action
The Conference secretariat has estimated the average total annual cost (1993-2000) of implementing the activities of this programme to be about $100 million, including about $40 million from the international community on grant or concessional terms. These are indicative and order-of-magnitude estimates only and have not been reviewed by Governments. Actual costs and financial terms, including any that are non-concessional, will depend upon, inter alia, the specific strategies and programmes Governments decide upon for implementation.b. Scientific and technological means
Monitoring of climate change and its impact on freshwater bodies must be closely integrated with national and international programmes for monitoring the environment, in particular those concerned with the atmosphere, as discussed under other sections of Agenda 21, and the hydrosphere, as discussed under programme area B above. The analysis of data for indication of climate change as a basis for developing remedial measures is a complex task. Extensive research is necessary in this area and due account has to be taken of the work of the Intergovernmental Panel on Climate Change (IPCC), the World Climate Programme, the International Geosphere-Biosphere Programme (IGBP) and other relevant international programmes.
The development and implementation of response strategies requires innovative use of technological means and engineering solutions, including the installation of flood and drought warning systems and the construction of new water resource development projects such as dams, aqueducts, well fields, waste-water treatment plants, desalination works, levees, banks and drainage channels. There is also a need for coordinated research networks such as the International Geosphere-Biosphere Programme/Global Change System for Analysis, Research and Training (IGBP/START) network.c. Human resource development
The developmental work and innovation depend for their success on good academic training and staff motivation. International projects can help by enumerating alternatives, but each country needs to establish and implement the necessary policies and to develop its own expertise in the scientific and engineering challenges to be faced, as well as a body of dedicated individuals who are able to interpret the complex issues concerned for those required to make policy decisions. Such specialized personnel need to be trained, hired and retained in service, so that they may serve their countries in these tasks.
There is a need, however, to build a capacity at the national level to develop, review and implement response strategies. Construction of major engineering works and installation of forecasting systems will require significant strengthening of the agencies responsible, whether in the public or the private sector. Most critical is the requirement for a socio-economic mechanism that can review predictions of the impact of climate change and possible response strategies and make the necessary judgments and decisions.Appendix: The Hadley Centre Impacts of climate change on water resources Summary The implications of the new Hadley Centre climate scenario for water resources stress were assessed by first simulating river runoff with a macro-scale hydrological model, calculating changes in national water resource availability (taking into account imports from upstream), and comparing the estimated volume of water available for use with the amount withdrawn by water users. The baseline water availability and use data, together with the scenarios for future water use, were taken from work undertaken for the 1997 Comprehensive Assessment of the Freshwater Resources of the World. The first map shows the estimated change in 30-year mean annual runoff by the 2050s as compared with the baseline period 1961 to 1990. Runoff increases in high latitudes, South East Asia and some equatorial regions, but decreases substantially in Europe, most of Africa, the Middle East, eastern North America, and much of the Amazon basin. These changes can be very large in percentage terms. The rise in temperature will also affect the timing of streamflow through the year, with particularly large changes in those parts of the world -- eastern Europe, the northern United States, and parts of east Asia -- where the higher temperatures mean that a much smaller proportion of winter precipitation falls as snow to be stored on the land surface until the spring melt. In these areas, winter flows will increase and spring flows decrease. One measure of national water resource stress is the ratio of water used to water available (although this hides within-country variations and the risk of stress during drought conditions), and countries using more than 20% of their total annual water supply are generally held to be exposed to water stress. The second map shows the effect of climate change on water stress by the 2050s, relative to the effects of population growth, and indicates that water resource stresses in many of the poorest countries would be exacerbated by climate change. Climate change would lead to an additional 66 million people living in countries using more than 20% of their total potential resource by 2050, and an additional 170 million people would be living in countries using more than 40% of their resources.
Estimated change in 30-year annual
runoff (millimetres per year) by the 2050s, compared with the baseline period.
Change in water stress, due to climate change, in countries using more than 20% of their water resources. 1998 Climate Change and its impacts. Highlights from the ongoing UK research programme: A first look at the results from the Hadley Centers new climate model Impacts of climate change on water resources, Summary Contributor: Nigel Arnell, University of Southampton http://www.met-office.gov.uk/sec5/CR_div/Brochure98/water.html