South Africa is fundamentally a semi-arid and water scarce country with a mean annual rainfall of 490mm, which is half the world average, with only 9% of that rainfall being converted to river runoff. Rainfall displays a distinct decreasing trend from east to west and is highly variable within and between years with recurrent droughts. This results in highly variable river levels, dam storage and groundwater storage over time (DWAF 2008).
Ecological processes and socio-economic development are often limited by water availability (Meadows 2006). Figure 3 demonstrates that the majority of catchments in South Africa use more water than is available on an annual basis (DWAF 2005). In 2004, 98% of South Africa's surface water yield, as well as 41% of the annual usable potential of groundwater were allocated to use (Blignaut et al., 2009). Of this allocated use, 60% went to agricultural activities, 27% to domestic demand, 23% to urban needs, 4% to rural, mining and bulk industry 6%, afforestation 3% and power generation 2% (DWAF 2009).
The close interconnectedness between the climate and the hydrological cycle means that water resources will be impacted by climate change and this will place increased pressure on water resources and ultimately threatening the sustainability of future availability (DWAF 2009). Schulze et al. (2001) states that water resources are directly impacted by current climate variability and it is expected that climate change could impact resources significantly in the future. The most significant impacts of climate change on water resources are the potential changes in the intensity and seasonality of rainfall. While some regions may receive more surface water flow, future problems are likely to include water scarcity, increased demand for water, and water quality deterioration. The overall impact of climate change on water resources remains uncertain and will vary significantly from place to place within South Africa. This complicates the planning and adaptation responses required to ensure sufficient future water supplies.
Despite the influence of climate change, it is predicted that by 2025 South Africa will be using up the majority of its surface water resources (Fig 4). This is as the sustainability of water resources and ultimately the availability of water in the future will depend on both supply and demand pressures (Arnell 1999). Supply pressures include climate change, environmental degradation where for example pollution reduces the amount of clean water available for use. Demand pressures include population growth and density which lead to increased demand for domestic, industrial and agricultural water use, as well as knock on effects of the management of water usage (Arnell 1999).
The review below considers firstly the key drivers that complicate and determine the water availability in South Africa, since climate change is not the single factor determining future water availability. The second section reviews the predicted impacts of climate change on South African water resources with the last section summarising the potential responses to the expected impacts.
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| Figure 3: 2005 Annual water balance in South African catchments based on data from the Department of Water and Forestry (Source: Colvine et al. 2009, Water Resources and Climate Change Case Study, South African Risk and Vulnerability Atas). |
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| Figure 4: Water demands and availability projections for 2025 projections for each province of South Africa where water availability is indicated by blue bars, water use by green bars and water development potential by red bars (DWAF 2009). |
Key drivers of change in the water sector
The nature and rate of economic growth impact on water, both in terms of abstraction and discharge. Energy, agriculture, forestry and mining utilise a significant proportion of the water available in South Africa and as such the water sector needs to align the provision of water with the spatial and sectoral growth of the economy. Just as economic change impacts on water requirements, social change (such as migration) affects the nature of services to be provided. Currently, water managers need to deal with a range of challenges such as circular migration between rural and urban areas, growing informal settlements on the margins of towns, and questions about the amount of free basic water that should be provided to vulnerable households and what service options will meet the needs of such households in the most effective manner (DWAF 2008).
Another challenge is that much of South Africa's water storage, distribution and monitoring, treatment and waste water collection infrastructure is aging and needs refurbishment or replacement. Effective infrastructure maintenance can result in sustainable water services and more efficient use of water which will offset some of the increased demand for water brought on by economic growth (DWAF 2008). On the other hand, increased water demands from higher standards of living, growing industrial and mining use, and failing water and wastewater infrastructure have had considerable impacts on water quality. Poor water quality has significant social, health and economic impacts, as well as negative impacts on aquatic ecosystems.
Institutional arrangements have been continuously changing since 1994, which adds to the complexity of dealing with the aforementioned challenges as well as to the way in which the water sector responds to water for growth and development (DWAF 2008). The National Water Act of 1998, however, provides a new institutional framework for water management in the country and is considered one of the most comprehensive examples of water legislation in the world, based on equitable water allocation, promoting economic growth, environmental integrity and poverty reduction.
Predicted impacts of climate change
Blignaut et al. (2009) found that South Africa has been approximately 2% hotter and at least 6% drier over the ten years between 1997 and 2006 compared to the 1970s. Rainfall trends are more difficult to determine and significant regional differences are evident in Southern Africa, which has experienced a marked inter-decadal variability (Schulze et al., 2001). Detailed local-level analyses of the historical rainfall record have indicated that the patterns are spatially complex, particularly in mountainous terrain, and the scale of observation and density of climate stations can influence the outcome significantly. For example, Mackellar et al. (2008) have shown from the relatively comprehensive historical rainfall record for rangelands in Namaqualand, South Africa, that some areas, which have exhibited a significant increase in rainfall since 1950, compared to areas only 50 km away, which have shown a significant decrease. Evidence shows that rainfall variability in South Africa as a whole has changed notably since the 1960s, with increased interannual variability, predominantly in the form of more intense and widespread droughts. In addition, large parts of South Africa have experienced a shift toward increasing probabilities of extreme rainfall events (Mason et al., 1999).
Higher temperatures will result in greater evaporative losses from dams as well as from the ground surface (Fauchereau et al., 2003). With higher temperatures more irrigation will be required for agriculture and more water will be needed for cooling of industrial equipment and processes. As previously mentioned, rainfall intensity is likely to increase, but this may not necessarily translate into an increase in the total rainfall. The First South African Country Study on Climate Change (DEAT 2000) bases its hydrological predictions of climate change on two Global Circulation Models which both indicate a greater intensity of rainfall events in the eastern part of the country and accentuated flooding in the associated rivers. This positive effect on runoff, however, is offset by longer dry spells and a significantly more variable hydrological response (Meadows 2006). Such changes in rainfall amount, timing and evaporation will have a significant impact of South Africa's surface water infrastructure such as storage systems and inter-basin transfer schemes, which provide the bulk water supply.
In areas where the infrastructure is less development, groundwater extraction is common and in such cases water table levels and recharge rates will be affected by climate change (Ziervogel et al., 2006). Both the timing and quantity of rainfall affect recharge rates of groundwater (Bouraoui et al., 1999). In semi-arid areas, groundwater recharge is driven by extremely heavy rainfall events and subsequently if these events become more frequent groundwater recharge may increase. During times of decreased rainfall, however, both groundwater recharge and surface runoff are reduced more than the reduction in rainfall. In a scenario for Bredasdorp, Western Cape, it is estimated that an 8% reduction in precipitation results in a 31% reduction in groundwater recharge, and 30% reduction in surface runoff (Mukheibir 2007). In addition, Schulze (2000) estimated mean annual runoff anomalies in the western parts of southern Africa and found marked runoff reductions. Arnell (1999) predicted a substantial reduction of runoff in three major river basins of southern Africa; 40% in Zambezi 40%, 30% in Limpopo and 5% in Orange basins. The models suggest also suggested a decrease in the volumes of low flows in all three rivers (Arnell 1999).
Predicted higher temperatures and lower flows may result in widespread decreases in water quality. The presence of sediments, nutrients, dissolved organic carbon, pathogens and pesticides will increase due to higher water temperatures, more intense rain and longer periods of low flow (Meadows 2006). This will result in increasing human health risks, costs of water treatment, and negative impacts of freshwater, estuarine and coastal ecosystems. Blue-green algae (cynobacteria), for example, are more likely to bloom in warmer water and the toxic and clogging effects of these blooms could have serious consequences for drinking water supply and irrigated agriculture. In addition, as sea levels rise salt water will intrude into estuaries and coastal groundwater tables, which are an important source of bulk water in some areas.
To date, the hydrological record shows that no effects can be unambiguously attributed to climate change, or mixed climate change effects. The impacts of climate change are likely to be exacerbated by changes in land use and poor land-use management (Meadows 2006). The political and practical imperative to improve access to water for both rural and urban poor will create further stress on the hydrological system as a result of the increased human demand (Schulze et al., 2001). A case study conducted for the City of Cape Town showed that reduced streamflow response in the future, together with elevated water demand against a limited supply capacity, will soon result in the permanent inability to meet supply yields (Meadows 2006). The challenge for the water sector is to manage this uncertainty and to continue to provide reliable water supply for social and economic purposes. These uncertainties also raise critical questions around the nature of economic growth and development that South Africa will be able to sustain.
Adaptation responses
Managing, mitigating and adapting to the aforementioned impacts are difficult due to the unpredictable nature of the change. Adaptation to climate change will require an improved understanding of our water balance, water demand management, as well as strengthening engineering and community based capacity to respond to new water supply challenges. Ziervogel et al. (2006) states that South Africa needs to revaluate water intensive development such as irrigated agriculture and certain types of mining, which is likely to increase local vulnerability as it increases exposure to water stress. DWAF (2008) states that priority needs to be given to developing robust strategies to ensure that demand matches supply, even where water availability is reduced. In addition, new water systems need to be designed and managed in a way that will accommodate future higher demands, increases in temperature and rainfall variability. Consequently, institutions need to encourage technical appropriate technology that range from large-scale water provision for economic growth through to micro-level processes to provide water to rural development. Water institutions will have to develop greater capacity to manage risk, to manage uncertain conditions, and therefore to adapt more readily to new and different conditions. As a result, local municipalities will need to manage increased run-off and stormwater drainage, and strengthen their disaster management systems.
Key opportunities for adaptation at the household level include recycling and re-use, desalination, and rainwater harvesting. Water conservation (WC) and water demand management (WDM) strategies are becoming a fundamental part of adaptation. These require changes in behaviour at the municipal, household and personal level, which include actions such as leakage detection and repair, leakage repair beyond the meter, use of water efficient fittings, and user education. Other decentralised water supply options, such as rainwater tanks, grey water re-use and boreholes, are also being considered as part of municipal WDM strategies.
Historically, water resources management in South Africa has focused on surface water, resulting in an extensive network of dams, inter-basin transfers, and pipelines. However, recent work has revealed significant reserves of groundwater that are not being fully utilized (Fig 5). Since most water stored in catchments is stored in aquifers underground groundwater can provide an important buffer against more uncertain rainfall future. This has implications regarding the infrastructure required to access this water, management systems and capacity, and planning at the municipal and national levels. Further, the aforementioned increase in higher-intensity rainfall events supports the argument for increased storage capacity as an adaptation strategy. There is significant scope for increased underground storage through managed artifical aquifer recharge, which DWAF is promoting as an integral part of water resource planning and catchment management. While not all aquifers are suitable, in appropriate areas artificial recharge costs a fraction of other storage options, and can be implemented incrementally thus saving on initial capital outlays. The potential for increased use of groundwater and underground storage heightens the importance of minimizing water contamination, from mining, industrial, agricultural and domestic sources.
Being able to respond in an adaptive manner to climate change requires good information. Institutions will need to identify water use trends, areas vulnerable to climate change and opportunities to respond to the emerging challenges. Secondly, researchers need to determine the impacts of climate on the water sector, such as impacts of extremes, variability, groundwater recharge, consequences for water quality, as well as conflicts over shared international waters and vulnerability of communities (Schulze 2000). Effective monitoring of the state of the country's water resources, water use, water infrastructure and institutional performance, is increasingly important to inform decision making on availability, allocation, and pricing. Lastly, the National Water Act, the water management institutions that it creates (such as Catchment Management Agencies), and the ongoing commitment to the delivery of basic water supply and sanitation infrastructure are all important adaptation actions already being instituted.
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| Figure 5: Balance of mean annual groundwater use versus recharge (expressed as a percentage) based on data from the Department of Water and Forestry (Source: Colvine et al. 2009, Water Resources and Climate Change Case Study, South African Risk and Vulnerability Atas). |
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