In order to better understand water use and availability trends, scientists divide the Earth’s surface into river basins. This feature examines some of the river basins that are the most important from an agricultural perspective. In each basin, the primary source of water is precipitation. Rain and snow feeds the river and its tributaries, as well as groundwater, ponds, and lakes. Precipitation also adds moisture to the soil, and crops take up the moisture through their roots.
Most crops around the world are grown using only the soil moisture provided by rainfall. When this moisture is insufficient, farmers apply more water through irrigation. Some rain or irrigation water evaporates without benefiting the plant, while some transpires through the plant's tissues during photosynthesis and returns to the atmosphere. Water transformed into vapor in either of these ways is not available for use again in that local area, so in practical terms, it is lost or "consumed."
Different crops have different water needs, which vary with the climate in which they’re grown. Scientists at the University of Twente in the Netherlands have used modeling techniques to estimate the amount of water consumed by the various crops grown in river basins around the world. These are the data we use in this feature.
Fortunately, there are things farmers can do to reduce water consumption. Instead of flooding fields or sprinkling, they can use drip irrigation, which cuts evaporation losses by delivering water directly to the roots of plants. Such techniques are particularly important in dry regions, where heavy water consumption is depleting rivers and even causing some to dry up for portions of the year, as is currently the case with the Colorado, the Indus, the Murray, the Rio Grande, and others.
Learn more about global water footprints from the Water Footprint Network and about rivers and watersheds from The Nature Conservancy. Find out how much water is consumed to make everyday things and try our water footprint calculator to get a snapshot of your own consumption. Also check out our water wiz puzzle for kids.
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