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1.8 Natürliche Oberflächengewässer als Reservoir für die globale Versorgung mit Süßwasser (Max M. Tilzer)

1.8 Natural surface waters as sources of freshwater – A way out of the global water crisis? (Max M. Tilzer)

Natural surface waters as sources of freshwater – A way out of the global water crisis?: In many parts of the world, freshwater requirements can no longer be met, despite the fact that the withdrawal of freshwater was increased by a factor of nine during the 20th century. The most serious consequences of inadequate freshwater supply are decreasing food production on irrigated land and serious threats to human health. Present attempts to alleviate water shortages mainly aim at increasing the quantities of water that can be made available. However, both large dams and large-scale irrigation projects lead to high water losses and to adverse environmental impacts that in the worst cases can offset their potential benefits. Due to the combined effects of population growth and economic growth, resource consumption including freshwater, is expected to rise further during the coming decades, especially in the lesser developed countries. Large-scale projects are planned in both China and India to redirect water from regions with excess water, to regions with water shortage. Negative environmental and social consequences of these and similar measures could be enormous. It is argued in this paper that a change of paradigm is necessary to solve the current freshwater crisis: Most important is greater emphasis on water quality, instead of merely attempting to increase the quantities of available water. Natural freshwater bodies could better serve as sources for freshwater than large reservoirs. However, because most large freshwater bodies are heavily polluted, using them more extensively would require a thorough clean-up. The experience in many industrial countries has shown that freshwater ecosystems recover from degradation within 10–20 years. The use of natural surface waters as sources of freshwater requires the definition of critical loading thresholds for plant nutrients and noxious substances in order to secure their water quality.