IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability

3.4.4 Water quality

Higher water temperature and variations in runoff are likely to produce adverse changes in water quality affecting human health, ecosystems, and water use (Patz, 2001; Lehman, 2002; O’Reilly et al., 2003; Hurd et al., 2004). Lowering of the water levels in rivers and lakes will lead to the re-suspension of bottom sediments and liberating compounds, with negative effects on water supplies (Atkinson et al., 1999). More intense rainfall will lead to an increase in suspended solids (turbidity) in lakes and reservoirs due to soil fluvial erosion (Leemans and Kleidon, 2002), and pollutants will be introduced (Mimikou et al., 2000; Neff et al., 2000; Bouraoui et al., 2004).

Higher surface water temperatures will promote algal blooms (Hall et al., 2002; Kumagai et al., 2003) and increase the bacteria and fungi content (Environment Canada, 2001). This may lead to a bad odour and taste in chlorinated drinking water and the occurrence of toxins (Moulton and Cuthbert, 2000; Robarts et al., 2005). Moreover, even with enhanced phosphorus removal in wastewater treatment plants, algal growth may increase with warming over the long term (Wade et al., 2002). Due to the high cost and the intermittent nature of algal blooms, water utilities will be unable to solve this problem with the available technology (Environment Canada, 2001). Increasing nutrients and sediments due to higher runoff, coupled with lower water levels, will negatively affect water quality (Hamilton et al., 2001), possibly rendering a source unusable unless special treatment is introduced (Environment Canada, 2004). Furthermore, higher water temperatures will enhance the transfer of volatile and semi-volatile compounds (e.g., ammonia, mercury, dioxins, pesticides) from surface water bodies to the atmosphere (Schindler, 2001).

In regions where intense rainfall is expected to increase, pollutants (pesticides, organic matter, heavy metals, etc.) will be increasingly washed from soils to water bodies (Fisher, 2000; Boorman, 2003b; Environment Canada, 2004). Higher runoff is expected to mobilise fertilisers and pesticides to water bodies in regions where their application time and low vegetation growth coincide with an increase in runoff (Soil and Water Conservation Society, 2003). Also, acidification in rivers and lakes is expected to increase as a result of acidic atmospheric deposition (Ferrier and Edwards, 2002; Gilvear et al., 2002; Soulsby et al., 2002).

In estuaries and inland reaches with decreasing streamflow, salinity will increase (Bell and Heaney, 2001; Williams, 2001; Beare and Heaney, 2002; Robarts et al., 2005). Pittock (2003) projected the salt concentration in the tributary rivers above irrigation areas in the Murray-Darling Basin in Australia to increase by 13-19% by 2050 and by 21-72% by 2100. Secondary salinisation of water (due to human disturbance of the natural salt cycle) will also threaten a large number of people relying on water bodies already suffering from primary salinisation. In areas where the climate becomes hotter and drier, human activities to counteract the increased aridity (e.g., more irrigation, diversions and impoundments) will exacerbate secondary salinisation (Williams, 2001). Water salinisation is expected to be a major problem in small islands suffering from coastal sea water intrusion, and in semi-arid and arid areas with decreasing runoff (Han et al., 1999; Bobba et al., 2000; Ministry for the Environment, 2001;Williams, 2001; Loáiciga, 2003; Chen et al., 2004; Ragab, 2005). Due to sea-level rise, groundwater salinisation will very likely increase.

Water-borne diseases will rise with increases in extreme rainfall (Hall et al., 2002; Hijioka et al., 2002; D’Souza et al., 2004; see also Chapter 8). In regions suffering from droughts, a greater incidence of diarrhoeal and other water-related diseases will mirror the deterioration in water quality (Patz, 2001; Environment Canada, 2004).

In developing countries, the biological quality of water is poor due to the lack of sanitation and proper potabilisation methods and poor health conditions (Lipp et al., 2001; Jiménez, 2003; Maya et al., 2003; WHO, 2004). Hence, climate change will be an additional stress factor that will be difficult to overcome (Magadza, 2000; Kashyap, 2004; Pachauri, 2004). Regrettably, there are no studies analysing the impact of climate change on biological water quality from the developing countries’ perspective, i.e., considering organisms typical for developing countries; the effect of using wastewater to produce food; and Helminthiases diseases, endemic only in developing countries, where low-quality water is used for irrigation (WHO/UNICEF, 2000).

Even in places where water and wastewater treatment plants already exist, the greater presence of a wider variety of micro-organisms will pose a threat because the facilities are not designed to deal with them. As an example, Cryptosporidium outbreaks following intense rainfall events have forced some developed countries to adopt an additional filtration step in drinking-water plants, representing a 20 to 30% increase in operating costs (AWWA, 2006), but this is not universal practice.

Water quality modifications may also be observed in future as a result of:

  • more water impoundments for hydropower (Kennish, 2002; Environment Canada, 2004),
  • storm water drainage operation and sewage disposal disturbances in coastal areas due to sea-level rise (Haines et al., 2000),
  • increasing water withdrawals from low-quality sources,
  • greater pollutant loads due to increased infiltration rates to aquifers or higher runoff to surface waters (as result of high precipitation),
  • water infrastructure malfunctioning during floods (GEO-LAC, 2003; DFID, 2004),
  • overloading the capacity of water and wastewater treatment plants during extreme rainfall (Environment Canada, 2001),
  • increased amounts of polluted storm water.

In areas where amounts of surface water and groundwater recharge are projected to decrease, water quality will also decrease due to lower dilution (Environment Canada, 2004). Unfortunately, in some regions the use of such water may be necessary, even if water quality problems already exist (see Section 3.2). For example, in regions where water with arsenic or fluorine is consumed, due to a lack of alternatives, it may still be necessary to consume the water even if the quality worsens.

It is estimated that at least one-tenth of the world’s population consumes crops irrigated with wastewater (Smit and Nasr, 1992), mostly in developing countries in Africa, Asia, and Latin America (DFID, 2004). This number will increase with growing populations and wealth, and it will become imperative to use water more efficiently (including reuse). While recognising the convenience of recycling nutrients (Jiménez and Garduño, 2001), it is essential to be aware of the health and environmental risks caused by reusing low-quality water.

In developing countries, vulnerabilities are related to a lack of relevant information, institutional weakness in responding to a changing environment, and the need to mobilise resources. For the world as a whole, vulnerabilities are related to the need to respond proactively to environmental changes under uncertainty. Effluent disposal strategies (under conditions of lower self-purification in warmer water), the design of water and wastewater treatment plants to work efficiently even during extreme climatic conditions, and ways of reusing and recycling water, will need to be reconsidered (Luketina and Bender, 2002; Environment Canada, 2004; Patrinos and Bamzai, 2005).