Agriculture is by far the world’s largest use of “blue water” (freshwater from streams, lakes, groundwater aquifers, etc) accounting for 70% of freshwater extraction globally and as much as 80-90% in some developing countries. While irrigation is a necessary part of food production in many regions of the world, it is essential to manage irrigation practices in a way that leaves enough water both for human use and ecosystem services. In some cases, water efficiency can be improved through better technology, such as drip irrigation. Appropriate crop selection is also an important factor, as non-native water intensive crops are often grown commercially that may deplete water levels.
The Irrigation Stress indicator (Water Stress in Irrigated Areas) is based on a measurement of water stress developed by the University of New Hampshire Water Systems Analysis Group. By overlaying data on irrigated areas with the measure of water stress, we were able to determine spatially where measures of extreme water stress (WMO, 1997) corresponded with irrigated areas. Water stress is present when rates of freshwater withdrawal exceed rates of replenishment though rainfall and natural flow. While countries can accommodate some rate of oversubscription in an isolated region via inter-basin transfer, ultimately overdrawing a water resource diminishes surface water, which degrades habitat for plants and animals. Oversubscription of groundwater for irrigation also causes land subsidence and increasing salt-water intrusion, and depletes the amount of water available for domestic consumption. The target for this indicator is for each country to experience no extreme water stress in irrigated areas.
115 countries have a proximity-to-target score between 90 and 100, indicating minimal or no water stress in their irrigated areas, while another 34 countries score a 70-90 on the proximity-to-target scale, indicating problems in some areas. A dozen countries score 50 or less, indicating very serious threats to the sustainability of irrigation: Yemen, Saudi Arabia, Libya, Kuwait, Egypt, Mauritania, Niger, Morocco, Jordan, Somalia, Djibouti and Namibia. Even moderate levels of irrigation water stress in large producers with high dependence on irrigation, such as China, the United States, Egypt, Pakistan, India and Australia, could potentially have noticeable effects on global food supply. Of countries with a high proportion of land under irrigation, over 90% of lands in Taiwan and Thailand are unstressed, and in Mali the figure is also quite high, at 85%.
