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The High Plains, or Ogallala, Aquifer is a large geologic formation of porous sand that underlies approximately 200,000 square miles (520,000 hectares)[1] in the U.S. Great Plains (see figure). The vast aquifer supplies water for most of this region's agricultural, domestic, and industrial uses. The response to growing water scarcity in this region may serve as a useful model for adaptation to climate change (37).
By 1980, some 150,000 agricultural irrigation wells were pumping water from the High plains Aquifer. Use of groundwater rose steadily from 7 million acre-feet (18.6 billion cubic meters)[2] in 1950 to 21 million acre-feet by 1980 (117). In these early days of irrigation, public information about irrigation technology and the status of the aquifer was limited (118). Waste was obvious, and widespread pumping from the aquifer was causing groundwater tables to drop. Serious declines in groundwater occurred in the southern Plains, with water tables dropping more than a 100 feet (30 meters) in parts of Texas (43). In Kansas, almost 40 percent of available groundwater had been withdrawn by 1980. With declining groundwater in Kansas came increased threats to critical wetland habitats used by the whooping crane. A groundwater resource that once seemed inexhaustible appeared, by 1980, to be in danger of eventually running dry.
Declines in the aquifer resulted in increased irrigation-pumping costs because it takes more fuel to pump from lower depths. This increased cost has in turn prompted technical and institutional adaptations. A survey of agricultural water users across the High Plains Aquifer region found that the preferred technical adaptations to declining groundwater levels were increased irrigation efficiency and the practice of conservation tillage (51). Under conservation tillage (e.g., no-till and reduced-till management), crop stubble is left on the field after harvesting, shielding soils from sun and drying winds. A switch to low-pressure irrigation systems in the southern Plains States (53) increased irrigation efficiency by greatly reducing evaporative water losses. Overall irrigated acreage has also declined, and many farmers have switched to low-water intensity crops such as wheat, cotton, and sorghum (66).
Institutional responses to scarcer groundwater on the High Plains have occurred at local and regional levels (48). The effectiveness of local policy has varied from State to State. Kansas, for example, passed a ground water management law that made possible the formulation of regionally controlled groundwater management units (66). These units provide orderly development of the High Plains Aquifer with tools such as the spacing of wells, limits on numbers of wells, metering of water use, and promotion of water conservation. Areas of Nebraska have imposed similar restrictions and metering requirements. The Cheyenne Bottoms Wildlife Area of Kansas is a 13,000-acre (5,200-hectare)[3] wetland that provides critical habitat for the whooping crane and some 5 million other migratory waterfowl that pass through each spring. The Kansas State Engineer has been able to impose restrictions on groundwater pumping in order to protect recharge rates into this wetland.
Texas, the State that could benefit most from strong groundwater governance, has rather weak groundwater management institutions (92). Unlike the other 49 States, Texas uses an absolute ownership rule in determining rights to groundwater. The rule, based on English common law, states that an owner of a parcel of land owns from the "sky above to the depths below" (92), which includes the water on, above, and below the surface. The absolute ownership rule has proved to be a formidable disincentive for landowners to agree to regulation of their water at the local level. Nevertheless, in the High Plains of northwest Texas, increasing water scarcity has resulted in innovations in the institutions for coordinating groundwater use and promoting water conservation.
The 5.5 million acres in the 15 northwest Texas counties that constitute the High Plains Groundwater Conservation District No.1 (44) receive just 12 to 16 inches (30 to 41 cm) of precipitation per year, but overlie part of the Ogallala Aquifer. Irrigation with groundwater pumped from the aquifer has allowed the region to grow large quantities of cotton, barley, sorghum, and corn for many years (74). The High Plains District was created in 1951 largely to address the needs for groundwater conservation. The District has been "dedicated to the principle that water conservation is best accomplished through public education" (44). Accordingly, the District focuses its efforts on research and demonstration projects, publishing free information about groundwater use and methods for conserving water, performing on-farm water-efficiency testing, and carefully monitoring groundwater levels and water quality.
One of the earliest District efforts was to reduce open-ditch losses. Water losses from open ditches were as high as 30 percent per 1,000 feet of ditch (44). The District performed economic analyses that showed farmers it would be cost-effective to stop losses (118). As of 1989, 12,097 miles (19,500 kilometers)[4] of underground pipeline had been laid to replace open ditches (44). Cost effective systems for recovering irrigation tail water were also developed and demonstrated by the District (74). New technology in the form of time-controlled surge valves for furrow irrigation and low-energy precision-application (LEPA) methods for spray irrigation systems were widely demonstrated and promoted by the District. Surge valves and shortened furrows resulted in 10 to 40 percent improvements in furrow-irrigation water losses, while LEPA systems reduced center-pivot irrigation losses from around 40 percent to as low as 2 percent (W. Wyatt, cited in ref. 74; 44). In 1978, the High Plains District in conjunction with the U.S. Department of Agriculture's Soil Conservation Service initiated an on-farm water-efficiency evaluation program. In many cases, suggested water and energy savings were sufficient to pay back farmers' costs within 1 or 2 years (74).
The High Plains District has a goal of reaching an equilibrium between groundwater withdrawals and aquifer recharge, as measured during a 5- or 10-year average. So far, net groundwater depletions in the Ogallala Aquifer underlying the District have declined from a 5-year average of 1.4 billion gallons per day (bgd) (15.3 billion liters per day)[5] in 1966-71 to an average of 0.43 bgd in 1981-86 and 0.16 bgd in 1986-91. A 25 to 40 percent cutback in groundwater use has been achieved (74); part of the cutback can be attributed to reductions in irrigated and planted area and several years of above-average rainfall (118, 44). Nevertheless, improvements in water-use efficiency and aquifer sustainability have led District officials to conclude that their voluntary, education-based approach to water conservation has been successful (44, 119).[6]
The various societal and individual responses to growing water scarcity suggest that farming regions may adapt well to a slowly changing climate. Perhaps more impressive than the ability of farmers to undertake technical adaptation has been the relative ease with which institutions have developed to promote more efficient use of scarce water resources. Still, despite the positive changes that have occurred in this region, one should not be overly optimistic. Groundwater depletion continues in much of the aquifer---even though at reduced rates and many farmers face a reduction in future farm income as they decrease their water use.
2 To convert acre-feet to cubic meters, multiply by 1,230.
3 To convert acres to hectares, multiply by 0.405.
4 To convert miles to kilometers, multiply by 1.609.
5 To convert gallons to liters, multiply by 3.785.
SOURCE: Office of Technology Assessment, 1993.