出典:Wikipedia
出典:『Wikipedia』 (2011/06/07 14:02 UTC 版)
Researchers define water stress and water scarcity in different ways. For example, some have presented maps showing the physical existence of water in nature to show nations with lower or higher volumes of water available for use. Others have related water availability to population. A popular approach has been to rank countries according to the amount of annual water resources available per person. For example, according to the Falkenmark Water Stress Indicator, a country or region is said to experience "water stress" when annual water supplies drop below 1,700 cubic meters per person per year. At levels between 1,700 and 1,000 cubic meters per person per year, periodic or limited water shortages can be expected. When water supplies drop below 1,000 cubic meters per person per year, the country faces "water scarcity". The Unitied Nations' FAO states that by 2025, 1.8 billion people will be living in countries or regions with absolute water scarcity, and two-thirds of the world population could be under stress conditions. Water stress is considered "set to become a permanent feature of British life".