Besides the effects on the global water cycle, higher water temperatures due to climate change are projected to affect water quality and exacerbate many forms of water pollution and thus the environmental and agricultural conditions.
Changes in Water Temperatures due to climate change
River and lake water temperatures are expected to show the most immediate reaction to climate change, as they are in close balance with air temperature. In Europe, North America and Asia, surface water temperatures have warmed by 0.2 to 2°C in lakes and rivers during the last 50 years. In the large African lakes, the deep-water temperatures have warmed by 0.2. to 0.7°C in the last century, especially this development of deep-water temperatures reflect long-term trends (IPCC).
Environmental Impacts of higher water temperatures
Biodiversity
Many species are temperature sensitive, and abrupt water temperature rises could have important implications for some aquatic species. Changes in the water temperature may deplete certain species and on the other hand trigger the establishment of invasive species with unknown consequences for ecosystem structures. Daufresne and Boet (2006) for example underline that species composition, diversity, global abundance and size structure of fish communities exhibited important trends related to water warming in large rivers. Also changes in productivity and phenological shifts (including earlier fish migration) are reported (IPCC Technical Paper).
Water Quality
Increasing water temperature may also compound the impacts of eutrophication and acidity changes in the ecosystem structures (WWAP 2012).
Due to higher temperatures, increased thermal stability and altered mixing patterns in lakes may result in reduced oxygen concentrations and an increased release of phosphorus from the sediments and cause algal blooms that restructure the aquatic food web. There have been decreases in nutrients in the surface water and corresponding increases in deep-water concentrations of European and East African lakes because of this reduced upwelling due to greater thermal stability. Reduced oxygen concentrations will reduce aquatic species diversity, especially in cases where water quality is impaired by eutrophication. An increased bacteria and fungi content will also be promoted through higher water temperatures. On the other hand water quality could be improved during the winter and spring time in some regions due to an earlier ice-breakup and higher oxygen levels.
Water pollution
As most chemical reactions and bacteriological processes run faster at higher temperatures, higher water temperatures due to climate change are projected to increase different forms of water pollution. Higher water temperatures, increased precipitation intensity and longer periods of low flows are projected to exacerbate many forms of water pollution and increase pressure on diseases such as malaria, schistosomiasis and diarrhea. For example, climate has been found to influence cholera dynamics in Bangladesh, Peru and five countries in Africa (WWAP 2012).
Consequences for agricultural water management
The temperature of water used for agriculture has high influences on the environment, soil quality and crops. An option to cope with water scarcity is supply enhancement which includes the reuse of wastewater. Given the mentioned impacts of higher temperatures on water quality, harmful effects could be the consequence when using wastewater for irrigation purposes. The growth of waterborne toxins and parasites will create an additional risk of using this water for food production, especially in areas where a greater dependence on irrigation with wastewater is needed to address crop moisture deficits generated by heat waves and greater precipitation variability. (FAO 2012; Padgham, J. 2009). The World Health Organisation (WHO) has developed appropriate guidelines which are available in ‘WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater, Volume ii, Wastewater Use in Agriculture’.
From 2004, GTZ has implemented the project “Reclaimed Water Irrigation“. The guidelines elaborated in the context of the “Reclaimed Water Project” are available in Guidelines for Reclaimed Water Irrigation in the Jordan Valley
References
- IPCC (2008): IPCC Technical Paper VI - June 2008. Climate Change and Water. Bates, B.C., Z.W. Kundzewicz, S. Wu and J.P. Palutikof, Eds. IPCC Secretariat, Geneva, 210 pp.
- Koelle, K., Rodo, X., Pascual, M., Yunus, M. and Mostafa, G. (2005): Refractory periods and climate forcing in cholera dynamics. Nature, Vol. 436, pp. 696–700.
- Padgham, J. 2009. Agricultural Development under a Changing Climate.Opportunities and Challenges for Adaptation. Joint Discussion Paper, Agriculture and Rural Development and Environment Departments, The World Bank.
- Rodo, X., Pascual, M., Fuchs, G. and Faruque, A. S. (2002) Enso and cholera: a nonstationary link related to climate change? In: Proc Natl Acad Sci USA, Vol. 99, pp. 12901–6.
- WWAP (World Water Assessment Programme). 2012. The United Nations World Water Development Report 4: Managing Water under Uncertainty and Risk. Paris, UNESCO
- Daufresne, M. and Boet,P. (2006): Climate change impacts on structure and diversity of fish communities in rivers. In: Global Change Biology 13, 2467–2478
