Every five years, the National Agricultural Statistics Service (NASS) conducts an Irrigation and Water Management Survey as a follow-up to the Census of Agriculture. Such a survey was conducted in 2018, and NASS indicates that the results of that survey will be made available in November 2019.
Consequently, the most recent data available on nationwide use of irrigation practices right now are from the survey conducted in 2013. In 2013, there were 229,237 farms with 55 million acres under irrigation in the United States. Irrigated area accounted for about one quarter of all land in farms in that year. Farmers in states west of the Mississippi River raised crops on nearly 48 million acres of irrigated land, accounting for 86 percent of the national total. In that survey, the top five states for irrigated agriculture were Nebraska (8.3 million acres), California (7.5 million acres), Arkansas (4.9 million acres), Texas (4.5 million acres) and Idaho (3.5 million acres).
Most of that irrigated farmland--56 percent of the total--was found on large farms with 1,000 acres or more. As of 2013, the primary row crops harvested under irrigation are corn, raised on 13.3 million acres with Nebraska, Kansas, and Texas as the largest states with such operations, soybeans grown on 7.4 million irrigated acres, with the largest number of such acres in Arkansas, Missouri, and Nebraska, and wheat, grown on 3.2 million acres, with Idaho, Texas, and California as the largest states. Irrigated acres only accounted for 15 percent, 10 percent, and 7 percent of the total harvested acres of those three crops respectively.
Vegetables were raised on another 2.9 million irrigated acres and fruit and nut tree orchards accounted for another 3.7 million acres of irrigated farmland. Farmers in California and Washington state dominated both sectors. Horticultural crops, flowers, and nursery crops are also grown under irrigation in greenhouse facilities with 1.4 billion square feet of irrigated space in those facilities nationally. Florida, California, Texas, and Michigan had the largest number of irrigated square feet in greenhouses as reported in the survey.
In 2013, about half of all irrigated farmland received all of its water from on-farm wells pulling up groundwater, about 5 percent of irrigated farmland received all of its water from on-farm surface sources, such as farm ponds, and about 17 percent of irrigated farmland received all of its water from off-farm surface water sources, such as reservoirs maintained by state or federal agencies. The remaining 28 percent received water from more than one source.
The structure of current U.S. water policy, which affects both the distribution and availability of water for irrigation purposes, consists of a combination of both federal and state laws and regulations. Since 1974, Congress has tried to take up and pass Water Resources Development legislation every two years, and prior to that year, similar legislation was generally referred to as the Rivers and Harbors Act, dating back to President Franklin Roosevelt’s New Deal period in 1938. This legislation generally provides resources for the Army Corps of Engineers to build or upgrade water-related infrastructure, such as port facilities and levees, locks and dams on rivers to enhance transportation, and dams, canals, aqueducts, and reservoirs, especially in the Western United States, to make water available for agriculture in otherwise arid regions. A 2006 study by the Congressional Budget Office estimated that between 1902 and 2004, the U.S. government spent $24 billion in nominal dollars on water infrastructure in the West, although some portion of this funding was eventually reimbursed by the affected states.
Federal investment in western water infrastructure and other federal statutes such as the Endangered Species Act gives certain federal agencies, such as the Bureau of Reclamation and the Fish and Wildlife Service, the legal authority to determine how to allocate water made available through that infrastructure.
For surface water from other sources, the allocation of rights to use for irrigation purposes is primarily governed by state laws. In the United States there are three different legal systems for allocating and regulating the use of surface waters; riparian rights, prior appropriation, and hybrid systems. Most states in the Eastern U.S., where fresh water is plentiful, follow the riparian rights system. States in the arid West use prior appropriation to allocate surface water. And some states have adopted elements of both systems into hybrid systems to fit their specific needs. Groundwater is regulated in similar manners in most states.
Recent droughts have caused some Western states to reconsider their traditional legal systems and bring new regulations to bear on the situation. In the wake of the extended drought between 2011 and 2017 in California, many farmers drilled wells to access groundwater for irrigation since they were unable to obtain sufficient surface water from state and federal agencies to keep their operations going. Concerns that the aquifer under the state would be at risk without placing some constraints on such wells, the state enacted the Sustainable Groundwater Management Act in 2014, which is designed to establish a sustainable groundwater management system for the state.
More recently, seven states in the West that rely on the Colorado River system for much of their water, both urban and rural, recently agreed to a drought contingency plan that would reduce water allocations in a systematic way to alleviate stress on the entire system. Finalized on May 20, 2019, it significantly reduces the chances that Lake Meade, a key reservoir on the system, would be exhausted in the event of a drought. However, it only binds the seven states (Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming) for seven years, so a longer term solution is obviously needed.