Stretching from South Dakota to the Texas Panhandle, the High Plains Aquifer covers much of the middle of the country, with parts of eight states relying on its groundwater reserves for agricultural, industrial and municipal purposes. Groundwater stored under the earth's surface in porous soil and rock can be accessed by drilling wells that pump the water to the surface. The aquifer recharges from rainfall as well as underground flows from streams and springs, a process that occurs at different rates depending on local geological features as well as the level of human use in the area.
The importance of water management and the vulnerability of regional agriculture became clear during the Dust Bowl of the 1930s, when a sustained period of severe drought caused major topsoil erosion and devastated agricultural output, worsening the economic impact of the Great Depression. By the 1950s, after agricultural production had resumed, large-scale irrigation using the High Plains Aquifer began, and it accelerated dramatically in the next few decades.
A Thirsty Breadbasket
The eight states that have territory above the aquifer — South Dakota, Wyoming, Nebraska, Colorado, Kansas, Oklahoma, New Mexico and Texas — are part of the traditional breadbasket of the U.S. interior, and water reserves from the High Plains Aquifer are vital to regional agriculture. In 2000, roughly 75 percent of total groundwater pumped in Kansas was used for irrigation. In 2010, Kansas, Nebraska and South Dakota combined for 20 percent of U.S. corn production, and these three states along with Oklahoma and Texas combined to produce 45 percent of the U.S. winter wheat crop. Kansas alone is responsible for 22 percent of the wheat crop and exported $1.1 billion worth of wheat in 2010 and an additional $850 million worth of feed grain, including corn. Given the volume of exports, changes in production of these staple grains in the United States impact the global market, particularly in countries such as China, Mexico and Nigeria — all of which are large importers of U.S. grains and where a dramatic decline in available supplies could undermine political stability.
Despite recent efforts to create a more sustainable strategy for groundwater allocation, studies by the U.S. Geological Survey and NASA show that areas of the High Plains Aquifer are still being overdrawn. Measurements from these studies show that while the northern reaches of the aquifer are still relatively well supplied, heavy groundwater pumping for irrigation and industry in parts of Kansas and the Texas Panhandle has brought aquifer levels down by as much as 45 meters (nearly 150 feet) since the 1950s. The rate of depletion has accelerated since 2000, with roughly one-third of total aquifer depletion since 1900 occurring between 2000 and 2008.
While the volume of water being used for irrigation actually declined during this period, several consecutive decades of above-average population growth in the region, along with a sustained period of extreme drought from 2000 to 2004, contributed to accelerating depletion. Much of the region remains in what has been classified as an exceptional drought. Prolonged groundwater depletion has not yet caused widespread declines in agricultural production, but there is growing anecdotal evidence of localized water shortages harming agricultural operations, evidenced by wells going dry as the water level declines and reduced agricultural output. Further declines in the water level will make accessing remaining groundwater more expensive and energy-intensive as wells are dug deeper, requiring more energy to pump the water to the surface. Increased operational costs for agricultural production in the United States could have a significant impact on both domestic and international food prices.
Since the 1940s and 1950s, groundwater policy in this region has been legally based on the prior appropriation doctrine, meaning water rights are granted in the order they are requested and not necessarily to those owning land immediately adjacent to the water supply in question. The first party to claim the water for a beneficial use, which most states define as use for agricultural or municipal purposes, attains a senior right to that amount of water. During periods of drought, those holding senior water rights were given priority to use their allocated share of water before junior water rights holders. While originally meant to protect against water shortages by prioritizing water use during periods of drought, the prior appropriation doctrine has failed to stop the over-allocation of water resources, with holders of both senior and junior water rights continuing to pump from the aquifer at a faster rate than the rate of recharge. This has caused regional groundwater reserves to diminish more quickly than expected and has contributed to groundwater and surface water shortages throughout the Great Plains.
The situation in Kansas illustrates the problems states have had managing water rights. The Kansas Water Appropriation Act of 1945 resulted in an over-allocation of groundwater from the High Plains Aquifer by retroactively granting too many water rights to those already holding wells at the time the law was passed. This legislation also overestimated the recharge rate at which precipitation would replenish groundwater reserves and underestimated the discharge rate at which groundwater flows into nearby sources of surface water. According to 2007 measurements, Kansas withdrew 5.28 billion cubic meters from the High Plains Aquifer. About 2.88 billion cubic meters came from the Ogallala Aquifer, where the estimated annual recharge rate is 0.86 billion cubic meters, far less than the annual rate of withdrawal.
Recently, western states have begun to implement policies that better recognize the relationship between surface and groundwater resources. Kansas has implemented minimum streamflow requirements that will restrict groundwater use in areas where surface water levels have dropped below the level needed to maintain water quality and fish and wildlife populations. While this may partially correct original overestimates of available water resources, it may not reverse the significant depletion that has already taken place.
Even though the pressures on the water supply are recognized, the uneven distribution of groundwater resources and the lack of coordination between state and local governments present a major challenge to comprehensive reform. Several states, including Kansas and Colorado, have adopted a localized approach to water management through the creation of groundwater management districts whose jurisdiction is usually no larger than the county level and can be as small as a city or town. Within these districts, groundwater commissions may establish regulations specific to that area and its individual water use patterns and determine procedures for monitoring and enforcement. However, fully monitoring levels of groundwater use by individual wells and water users exceeds the institutional and financial capacities of most states. There is also significant competition for limited resources and overlap between these local bodies and other state and federal groups, and the structure of authority and decision-making is often unclear.
Because of this, developments in state water policy have often been ad hoc and reactive in nature, with most major policy changes resulting from specific conflicts rather than a more comprehensive reform process, like that seen in the Colorado River Basin. And while most states have designated mechanisms for resolving low-level disputes, interstate water conflicts have reached as high as the U.S. Supreme Court.
Due to competition at the state and local levels, federal involvement may be necessary for comprehensive reform, but there is little historical precedent for this type of federal intervention into state water policy. While federal entities such as the Environmental Protection Agency have passed numerous regulations specific to preventing water pollution, they have not traditionally had a role in governing the allocation of water resources. Attempts by the U.S. government to exert control over groundwater conservation could encounter major political resistance from individual states and communities reluctant to relinquish control of such a vital resource.
Given the challenges to meaningful improvement in policies for managing existing groundwater resources, the development of alternative sources of freshwater such as desalination, recycling of wastewater or imports from water-rich areas may offer a partial solution to the growing problem of water scarcity. Several other water-scarce countries, including Singapore and Saudi Arabia, have devoted significant financial resources to developing desalination technology and rely heavily on this alternative source of fresh water.
While some coastal areas in the United States have begun developing desalination capabilities, these efforts have been plagued with regulatory, environmental and economic disputes. However, desalination technology is continually improving, which may make the process more energy efficient and cost-effective in the future, increasing its appeal in regions like the High Plains Aquifer. Rapid pumping of fresh water from the aquifer for irrigation and industrial water use has increased the rate of salt infiltration of regional groundwater, and a significant portion of the aquifer's current reserves contain too much salt to be used for agricultural or municipal purposes. Desalination would not necessarily slow actual rates of depletion, but it could increase the overall volume of groundwater reserves available for use. Development of efficient desalination infrastructure on the coasts could also allow desalinated seawater to be transported to water-scarce landlocked regions if necessary.
The United States has the resources to pursue a number of technological remedies to mitigate a water shortage crisis, which, while looming, is not imminent. However, without a coordinated approach to managing and allocating current groundwater reserves, overuse amid drought or near-drought conditions will continue to be a problem for the world's primary agricultural exporter.