Irrigation has allowed for a diversification of crops in the Great Plains. Depending upon the future changes in temperature and precipitation and the impacts those changes have on particular crops, agricultural demand for water resources is likely to increase in the future. One study, using results from the warmer climate model scenario used in this region, found that consumptive demand for irrigation water for perennial crops such as grass and alfalfa would increase at least 50% by the 2090s over current levels (average of 1961-90). However, the demand for consumptive water use for corn, which relies more on growing season precipitation, does not increase substantially because projections suggest a precipitation increase.

Water quality is a current constraining factor in the use of water. How water quality problems, (e.g., salinity, nutrient loading, turbidity, and siltation of streams) are managed affects the availability of water for agricultural and human use. Dams, diversions, channelizations, and groundwater pumping have influenced nearly all freshwater ecosystems in the Great Plains by altering riparian (along the waters edge) habitats, aquatic ecosystems (those growing or living in water), hydrological (water) cycles, and recreational opportunities.

Potential increases in drought and/or storm intensity could severely affect water quality. Non-point source pollution can contain contaminants from fertilizers, herbicides, pesticides, livestock wastes, salts (leftover from irrigation water that has evaporated), and sediments that reduce the quality of both surface water and groundwater drinking water supplies. Many small towns in the Great Plains already struggle to meet current drinking water standards. The projected increase in intense rainfall in the southern Great Plains could increase problems with runoff in urban areas or runoff of livestock wastes from feedlots.

The projected increases in temperature and droughts are expected to aggravate the current competition for water among the agricultural sector, urban and industrial users, recreational users, and natural ecosystems, as well as within each user community. Because water needs and available resources differ, changes such as a shift in the timing of precipitation will affect different users differently. Winter warming and an increase in winter precipitation could result in earlier and more rapid snowmelt from the Rocky Mountains. Such changes in the timing of snowmelt runoff from the Rocky Mountains is likely to necessitate changes and adjustments in the current system of water management in the Platte Basin, for example. In the South Platte Basin, water is taken from the streams/rivers in the spring and pumped strategically into nearby shallow groundwater aquifers such that the later release of the recharge meets downstream user needs at the appropriate time. This storage system along the South Platte is adapted to the current climate and timing needs of water users; with projected changes in climate, the present levels of release of recharge would not be likely to meet the timing or amount of the downstream users' water needs.

Water supply and demand, allocation and storage, and quality are all climate-sensitive issues affecting the regional economy. In each state, the allocation of water among competing uses is determined by the ownership of water rights and on an interlocking set of contracts and operating rules governing federal and other public water projects. Initial water allocations can be modified by market transactions (buying and selling), but the cost and laws relating to transferring water or water rights through markets varies considerably from state to state.

For example, laws restrict transfers from agricultural to non-agricultural uses in Nebraska. Water allocation decision-making among the various sectors (e.g., agriculture, energy, urban, wildlife, etc.) is a major challenge and has been marked by conflict, negotiation, or cooperation, depending on the setting. While interstate allocation issues have led to significant disagreement, there are promising signs of cooperation in the tri-state effort between Colorado, Wyoming, and Nebraska to address endangered species preservation along the Platte River. In addition, negotiations between urban centers and irrigators who are willing to sell their water rights or rent water owned by a community are becoming commonplace in some states. Management of both surface water and groundwater to meet diverse and increasing water needs is thus a major political and management concern in the region today and will likely become even more important under climate change.

Strategies for providing adequate water resources under changing climate conditions vary in focus and in cost. There are existing strategies that deal with droughts, chronic water shortages, extreme weather events and year-to-year climate variability. These strategies seek to improve and maintain soil, water, biotic, and land resources. Numerous cultural, economic, political, and social factors often inhibit a rapid and widespread adoption of practices that are more resilient to variations and changes in climate. This list of adaptation options is not exhaustive and should be used as a starting point for discussion and consideration of options.

• Diversify the techniques used to increase storage and availability of water, including: increase management of groundwater aquifers; enhance snowpack storage in mountains through forest management; adopt additional crop management practices intended to enhance soil moisture retention through use of crop stubble, wind breaks, and mulches; and adopt snow management strategies on the Plains. Broader application of such techniques could increase the quantity of stored water and enhance resilience to changing climatic conditions.
• Enhance scheduling schemes for irrigation, adjust crop yield target to match available water supplies, and/or change crops or even land use to increase the efficiency of overall use of water.
• Increase efficiency of irrigation application methods (such as precision farming) to decrease overall water consumption.
• Reduce consumptive water use in urban areas through conservation, xeriscaping (low water-use landscaping), and the use of gray water systems for irrigating landscapes. The effectiveness of such measures and distribution of impacts across various water users are likely to depend on a number of both natural and institutional factors. For example, more efficient water use in one location does not necessarily result in less overall water demand as less use at one point can simply allow increased use downstream. In addition, potential water quality issues could arise with repeated use of water by multiple users.
• Expand trading of water to increase options for drought management. Presently, this approach is more developed in some states than in others. For example, there are active water rental markets in Colorado along the Front Range of the Rocky Mountains, and many cities that have acquired water rights in advance of need routinely rent them back to agricultural users in normal water years. This practice provides a drought buffer for the urban users because the city can decide not to lease the water during drought years.
• Institute “water banking -- programs through the coordinated use of groundwater and surface water supplies and establishment of formal mechanisms to facilitate voluntary water transfers. This is a relatively new concept in the Great Plains region, but both Texas and Kansas have already instituted programs to encourage water banking.