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This Overview section

More detailed chapter from  "Foundation" report.

The National Assessment Overview and Foundation Reports were produced  by the National Assessment Synthesis Team, an advisory committee chartered under the Federal Advisory Committee Act, and were not subjected to OSTP's Information Quality Act Guidelines. The National Assessment was forwarded to the President and Congress in November 2000 for their consideration.

For background information on scenarios used in this assessment, see About Scenarios and Uncertainty and  Tools for Assessing Climate Change Impacts

   The projected climate-induced changes in water resources are likely to exacerbate the current competition for water among the agricultural sector, natural ecosystems, and urban, industrial, and recreational users.

KEY ISSUES • Alteration in Timing and Amount of Water • Changes in Climate Extremes • Invasive Species Effects on Economy and Ecology • Stress on Human Communities • Conservation of Soil Organic Matter

While farming and ranching are still the primary land uses of the Great Plains, urban areas provide housing and jobs for two-thirds of the region's people. Native ecosystems and agricultural fields intermingle with small rural communities and the expanding metropolitan centers. The region produces much of the nation's grain, meat, and fiber, including over 60% of the wheat, 87% of the sorghum, and 36% of the cotton. The region is home to over 60% of the nation's livestock, including both grazing and grain-fed-cattle operations. Recreation, wildlife habitat, and water resources are also found on the landscapes of the Great Plains. The Prairie Pothole region provides important habitat for migratory waterfowl. Surface water in rivers, streams, and lakes, and groundwater in aquifers provide water for urban, industrial, and agricultural uses, as well as riparian and aquatic ecosystems. Soil organic matter is a major resource of the Great Plains as it provides improved soil water retention, soil fertility, and long-term storage of carbon.

Climate determines many aspects of life on the Plains. For agriculture, weather determines the planting and harvesting dates for crops, livestock grazing and breeding seasons, and water availability. The high natural variability of climate is a characterizing feature of the region. Farmers and ranchers have survived by being adaptive and incorporating new technologies to buffer their production against the variable climate. For urban centers, the availability of water often constrains urban and industrial development. Dams, diversions, channels, and groundwater pumping have influenced nearly all freshwater ecosystems in the region. Ongoing social and economic changes in the Great Plains will continue to increase demands on the region's land and water resources and challenge its physical and social infrastructure. Climate change will present additional challenges to long-term planning for new infrastructure and the sustainable use of land and water.

Observed Climate Trends

Across the Northern and Central Great Plains, temperatures have risen more than 2�F (1�C) in the past century, with increases up to 5.5�F (3�C) in parts of Montana, North Dakota, and South Dakota. In the southern Great Plains, the 20th century temperature record shows no trend. Over the last 100 years, annual precipitation has decreased by 10% in eastern Montana, North Dakota, eastern Wyoming, and Colorado. In the eastern portion of the Great Plains, precipitation has increased by more than 10%. Texas has experienced significantly more high intensity rainfall. The snow season ends earlier in the spring, reflecting the greater seasonal warming in winter and spring.

Scenarios of Future Climate

Climate model scenarios project that temperatures will continue to rise throughout the region, with the largest increases in the western parts of the Plains. The Canadian model projects greater increases throughout the region than the Hadley model. The climate model projections, as well as other tools utilized in analyzing impacts, include a greater number of heat events -- three days in a row above 90�F -- a major cause of heat stress for people and livestock. Seasonally, more warming is expected in winter and spring than in summer and fall. Precipitation generally increases in the region in the Hadley model, and in the northern parts in the Canadian model. Precipitation decreases in the lee of the Rocky Mountains in both models. This is accentuated in the Canadian model, with decreases of up to 25% in an area centered on the Oklahoma panhandle and covering northern Texas, eastern Colorado, and western Kansas. Smaller decreases are seen in the Hadley model in a band from northern Texas through Montana. Although precipitation increases are projected for parts of the Great Plains, increased evaporation due to rising air temperatures are projected to surpass these increases, resulting in net soil moisture declines for large parts of the region.

Alteration in Timing and Amount of Water

Water supply, demand, allocation, storage, and quality are all climate-sensitive issues affecting the regional economy. Farming and ranching use over 50% of the region's water resources. Ground-water pumping for irrigation has depleted aquifers in portions of the Great Plains by withdrawing water much faster than it can be recharged. Under today's irrigation demands, water table levels are thus dropping in parts of the southern Great Plains. The projected climate-induced changes in water resources are likely to exacerbate the current competition for water among the agricultural sector, natural ecosystems, and urban, industrial, and recreational users.

Adaptations: It is possible that current strategies to deal with drought, water shortages, extreme weather, and variability could help the region cope with future climate change impacts. These strategies include switching to crops that use less water, retiring marginal lands, adopting conservation tillage, and enhanced watershed storage capacity and groundwater recharge activities. Water availability for crops could possibly be improved using new and existing technologies for crop residue management, wind breaks, mulches, soil carbon management, tillage practices, precision agriculture, and more efficient methods of water application. While these strategies would improve water use efficiency, adaptive strategies would also need to include maintaining water quality. Flexible policies and institutions would help to adapt to unanticipated hydrologic changes.

The potential for new patterns in climate extremes raises questions about the ability of current coping strategies to deal with future impacts.

A possible migration of invasive species across the Great Plains is a concern to stakeholders because the rapid rate of climate change is likely to be disadvantageous to native species. 

Changes in Climate Extremes

Extreme climate and weather events have major effects on urban and rural lives. The April 1997 flood put approximately 90% of Grand Forks, North Dakota under water and caused over $1 billion in damages. A short-term heat wave in July 1995 caused the deaths of over 4,000 feedlot cattle in Missouri. The severe drought from Fall 1995 through Summer 1996 in the agricultural regions of the southern Great Plains resulted in about $5 billion in damages. There is some chance that the projected increase in drought tendency in the Sand Hills of the Great Plains will result in expansion or shifting of sand dunes if vegetation cover is not maintained. The potential for new patterns in climate extremes raises questions about the ability of current coping strategies to deal with future impacts.

Adaptations: Better access to more accurate and timely information about near-term weather including extreme events, and longer-term forecasts could help reduce risk and uncertainty in decision making. For example, heat stress events are projected to occur more often in the central and southern Great Plains in the future. This information can help intensive-livestock operators weigh strategic decisions about investments in cooling systems. Real-time weather information can prepare them to implement an immediate response to cool their animals.

Invasive Species Effects on Economy and Ecology

The native grasslands, shrublands, forests, and riparian ecosystems of the Great Plains are home to a variety of plants and animals. Nearly 60% of the bird species that breed in the US do so in the Great Plains. Agriculture and urban development have disrupted these native ecosystems, and invasive species are currently a serious challenge in both native ecosystems and agricultural systems. For example, leafy spurge currently reduces grazing capacity on grasslands. Field bindweed lowers crop production in Kansas by $40 million a year. Projected climate change is likely to alter the current biodiversity. A possible migration of invasive species across the Great Plains is a concern to stakeholders because the rapid rate of climate change is likely to be disadvantageous to native species. The exact social costs will depend upon the particular invasive species or type of change in biodiversity.

Adaptations: Effective coping strategies would help provide plants and animals with habitats for adaptation such as maintaining a diversity of vegetation types and connectivity between the types. Preserving intact riparian areas, wetlands, and natural areas is likely to slow or reduce future invasions and is beneficial even in the absence of climate change.

Stress on Human Communities

Rural communities, already stressed by their declining populations and shrinking economic base, are dependent on the competitive advantage of their agricultural products in domestic and foreign markets. Large corporate enterprises, the result of agribusiness modernization and consolidation, have greater resources and technology with which to buffer themselves against both economic and climatic variability. Thus, a changing climate is an additional stress that disproportionately impacts family farmers and ranchers. In urban communities, the impacts of floods, heat waves, and other climate events is a crucial emerging issue with significant economic implications. Many poorer people can not afford air conditioning, insulation, substantial housing, and other means of coping with climate extremes. Therefore, climate change impacts will vary significantly by social and economic status.

Adaptations: Diversification within enterprises and rural communities could help to reduce risk and cope with the additional stress of climate change. Community-level dialogue is vital in identifying information needed by managers and in assessing policy options for climate change.

Conservation of Soil Organic Matter

Soil carbon is vital for retaining water and nutrients.  The amount of carbon stored in the soil is strongly influenced by past and present land management practices and weather patterns.  Overall, soil carbon is projected to decline in response to higher temperatures in both climate scenarios.  In some areas, climate changes reduce the decomposition of soil organic matter, resulting in increased soil carbon.