GEF

Unit 5  |  Toward Sustainable Water Systems 127 Since the 1960s, global agricultural productivity has skyrock- eted through a combination of widespread use of artificial fertilizers and pesticides, high-yield crops, and sharply increased use of irrigation. This Green Revolution has had profound impacts upon the developing world, allowing for dramatic rises in population and economic growth. While the Green Revolution has sharply reduced food insecu- rity in many countries, it has also placed a heavy burden on water resources because high-yield varieties of crops require five to ten times more water than conventional strains. As a result, countries that have benefited greatly from the Green Revolution, such as India and China, are also experiencing water stress as they rely on limited water supplies to allow for increased agricultural productivity. Fortunately, there is room for improvement. Historically, irri- gation has used water extremely inefficiently. In surface irrigation , water drawn from surface sources, such as rivers and lakes, is pumped directly onto agricultural fields. Other methods rely on overhead sprinklers and movable water pumps. Frequently, these irrigation techniques overwater fields or allow water to evaporate before it can nourish plants. Drip irrigation , which directly waters plant roots through ground-level tubes or hoses, is an increasingly widespread technique that can sharply reduce water use. Water manage- ment can also be improved by installing smart control systems such as rain sensors , soil-moisture sensors, and by making seasonal adjustments to irrigation systems. In the developing world, the bulk of agricultural land is not irri- gated and depends instead on rainfall. Farmers can conserve the rainwater that infiltrates the soil and directly nourishes plants by mulching, using intelligent soil conservation, and growing plants that are well-adapted to local climates. GREEN REVOLUTION A series of technological developments in agricul- ture which are credited with increasing agricultural production in developing countries. WATER STRESS When insufficient water is available in a given region to meet human needs. IRRIGATION The application of water to soil for growing plants. SURFACE IRRIGATION The introduction and distribu- tion of water over a surface, relying on gravity to deliver the water to plant roots. DRIP IRRIGATION A form of irrigation that saves water and fertilizer by allowing water to drip slowly to the roots of plants, either onto the soil surface or directly onto the root zone, through a network of valves, pipes, tubing, and emitters. RAIN SENSOR A switching device connected to an automatic irrigation system that causes the sys- tem to shut down in the event of rainfall.