The USGS Water Science School
Irrigation water use
Water Science water-use pages
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National Water Use Program
Information and Data
Irrigation water use
Think of what your supper table might be like if water was not used to irrigate crops. Do you think you could survive very long without heaping servings of eggplant, beets, brussels sprouts, and rutabagas? Irrigation water is essential for keeping fruits, vegetables, and grains growing to feed the world's population, and this has been a constant for thousands of years.
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). Estimates vary, but about 70 percent of all the world's freshwater withdrawals go towards irrigation uses (http://www.globalagriculture.org/report-topics/water.html). 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.
Center-pivot irrigation circles, Finney County, Kansas. Here, water is pumped from an underground aquifer and distributed through a giant sprinkler, up to 1/2 mile in length, that pivots around a central point.
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 had strong backs 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 or dripping faucet heads on wheeled tubes 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 techniques 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, evapotranspiration from plants, or is lost in transit, by a leaking pipe, for example.
Irrigation water withdrawals for the Nation, 2010
For 2010, total irrigation withdrawals were 115,000 Mgal/d, or 129,000 thousand acre-ft/yr, which accounted for 38 percent of total freshwater withdrawals and 61 percent of total freshwater withdrawals for all categories excluding thermoelectric power. Total irrigation withdrawals were 9 percent less than in 2005. Withdrawals from surface-water sources were 65,900 Mgal/d, which accounted for 57 percent of the total irrigation withdrawals, and were almost 12 percent less than in 2005. Groundwater withdrawals for 2010 were 49,500 Mgal/d, or 6 percent less than in 2005.
About 62,400 thousand acres were irrigated in 2010, an increase of about 950 thousand acres (1.5 percent) from 2005. About 31,600 thousand acres (51 percent) were irrigated with sprinkler systems, 26,200 thousand acres with surface (flood), and 4,610 thousand acres with microirrigation systems. The national average application rate for 2010 was 2.07 acrefeet per acre, or 11 percent less than the 2005 average of 2.32 acre-feet per acre.
Irrigation water withdrawals, by State, 2010
The majority of total U.S. irrigation withdrawals (83 percent) and irrigated acres (74 percent) were in the 17 conterminous Western States (west of solid line in figure 7), which are typical of areas where average annual precipitation is less than 20 inches and generally insufficient to support crops without supplemental water. Surface water was the primary source of water in the arid West, except in Kansas, Oklahoma, Nebraska, Texas, and South Dakota, where more groundwater was used. The 17 Western States cumulatively accounted for 93 percent of total surface-water irrigation withdrawals and 69 percent of total groundwater irrigation withdrawals.
Because the 17 Western States accounted for the majority of total irrigation withdrawals, changes in those States had a great effect on the overall total. Total irrigation withdrawals declined noticeably in Nebraska, Montana, Idaho, Colorado, and California. Groundwater irrigation withdrawals declined in the West and increased in the East, and surface-water irrigation withdrawals declined in both regions. Total irrigated acres increased in both regions --1 percent (568 thousand acres) in the West, and 2 percent (381 thousand acres) in the East. In the West, the total number of acres irrigated by the less-efficient surface-irrigation methods decreased by about 500 thousand acres, and the number of acres irrigated by more efficient sprinkler (including microirrigation) methods increased by about 1,080 thousand acres.
Trends in irrigation water withdrawals, 1950-2010
Since 1950, irrigation has represented about 64 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 135,000 and 139,000 Mgal/d between 1985 and 2000, and 115,000 in 2010 . 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 groundwater since 1950. During 1950, 77 percent of all irrigation withdrawals were surface water, most of which was used in the western States. By 2010, surface-water withdrawals comprised only 57 percent of the total. Groundwater withdrawals for irrigation during 2010 were more than double withdrawals in 1950. Most of this increase occurred from 1965 through 1980.
The trend in irrigation withdrawals is seen as the green bar in the chart below.
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