Throughout the world, irrigation (water for agriculture, or growing crops) is probably the most important use of water (except for drinking and washing a smelly dog, perhaps). Almost 60 percent of all the world's freshwater withdrawals go towards irrigation uses. Large-scale farming could not provide food for the world's large populations without the irrigation of crop fields by water gotten from rivers, lakes, reservoirs, and wells. Without irrigation, crops could never be grown in the deserts of California, Israel, or my tomato patch.
Irrigation has been around for as long as humans have been cultivating plants. Man's first invention after he learned how to grow plants from seeds was probably a bucket. Ancient people must have been strong from having to haul buckets full of water to pour on their first plants. Pouring water on fields is still a common irrigation method today -- but other, more efficient and mechanized methods are also used. One of the more popular mechanized methods is the center-pivot irrigation system, which uses moving spray guns that pivot around a central source of water. The fields irrigated by these systems are easily seen from the air as green circles. There are many more irrigation methods farmers use today, since there is always a need to find more efficient ways to use water for irrigation
When we use water in our home, or when an industry uses water, about 90 percent of the water used is eventually returned to the environment where it replenishes water sources (water goes back into a stream or down into the ground) and can be used for other purposes. But of the water used for irrigation, only about one-half is reusable. The rest is lost by evaporation into the air, transpiration from plants, or is lost in transit, by a leaking pipe, for example.
For 2000, withdrawals were an estimated 137,000 million gallons per day (Mgal/d), or 153,000 thousand acre-feet per year. Irrigation withdrawals were 40 percent of total freshwater withdrawals and, when excluding thermo-electric power, 65 percent of total freshwater withdrawals. Surface water accounted for 58 percent of the total irrigation withdrawals and ground water was 42 percent. About 61,900,000 acres were irrigated in 2000. Of this total acreage, about 29,400000, acres were irrigated with surface (flood) systems; 28,300,000 acres with sprinkler systems; and 4,180,000 acres with micro-irrigation systems. Application rates were calculated by dividing total withdrawals by irrigated acres. The average application rate was 2.48 acre-feet per acre for the United States.
The majority of withdrawals (86 percent) and irrigated acres (75 percent) were in the 17 conterminous western States. Irrigated acreage in these States were located in areas where average annual precipitation typically is less than 20 inches and is insufficient to support crops without supplemental water. Surface water was the primary source of water in the arid West and the Mountain States. Ground water was the primary source of water in the Central States. California, Idaho, Colorado, and Nebraska combined accounted for one-half of the total irrigation withdrawals.
[d] - Data for this pie chart are available.
Since 1950, irrigation has represented about 65 percent of total withdrawals, excluding those for thermoelectric power. Withdrawals for irrigation increased by more than 68 percent from 1950 to 1980 (from 89,000 to 150,000 Mgal/d). Withdrawals have decreased since 1980 and have stabilized at between 134,000 and 137,000 Mgal/d between 1985 and 2000. Depending on the geographic area of the United States, this overall decrease can be attributed to climate, crop type, advances in irrigation efficiency, and higher energy costs.
Surface water historically has been the primary source for irrigation, although data show an increasing usage of ground water since 1950. During 1950, 77 percent of all irrigation withdrawals were surface water, most of which was used in the western States. By 2000, surface-water withdrawals comprised only 58 percent of the total. Ground-water withdrawals for irrigation during 2000 were more than three times larger than during 1950. Most of this increase occurred from 1965 through 1980.
Sources and more information •
Estimated Use of Water in the United States in 2000, USGS Circular 1268:
• Irrigation water use, 2000:
Summary | Data table, by State | National map
U.S. Department of the Interior | U.S. Geological Survey
URL: http://ga.water.usgs.gov/edu/wuir.html
Page Contact Information: Howard Perlman
Page Last Modified: Friday, 07-Nov-2008 15:47:03 EST
