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For purposes of this paper, this region is defined as including North and South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, Tennessee, Kentucky, Arkansas, and a small part of Texas. In many areas of this 11-state region, increasing populations compete with agricultural, municipal, industrial, energy-producing, ecological, and recreational interests for water supplies from surface water and groundwater sources. Surface waters are held in bodies of water, such as lakes, rivers, and streams; groundwater, in contrast, is contained in underground aquifers -- layers of porous rock, gravel, or sand that contain water -- where wells can be drilled. Throughout the Southeast, water use is reaching the limits of supply, making this precious resource increasingly scarce.

Socioeconomic factors play a large role in the challenges facing this region's water sources. For instance, population increased by 30 percent in the Southeast from 1970 to 1990. By 1990, roughly 60 percent of the region's population lived in urban areas. Moreover, population in the Southeast has continued to grow through the 1990s -- in fact, the 544,000 square-mile southeastern “sunbelt -- is one of the fastest growing areas in our nation. Much of this growth occurred in coastal counties that are projected to grow another 40% between 2000 and 2025. The region's ever-increasing population has placed and will continue to place increasing demands on its water supply.

As the population of the Southeast has grown, so too has its economic base. During the past century this region has shifted from a largely agrarian economy to one driven by its natural resources, manufacturing and trade, technology, and tourism. Although the Southeast still produces about one-fourth of our nation's agricultural crops, trees now make-up the primary harvested natural resource in some of the region's states. The Southeast has become the Nation's “woodbasket -- producing over half of America's timber supplies. The region also produces a large portion of the nation's fish, poultry, tobacco, oil, coal, and natural gas. Both forestry and agriculture rely heavily on adequate supplies of water, yet both face increasing competition for and stress the quality of this resource.

Some of the most populated areas of this region are low-lying and the threat of salt water entering into its aquifers with projected sea-level rise is a concern. Although the sea level in all coastal areas of the United States is rising, some coastal regions of the Southeast could experience an effective sea-level rise of roughly 18 inches to 36 inches over the next 100 to 200 years. Beyond compromising the region's drinking water supply, even a more modest rise in sea level could cause flooding, erosion, and destruction of wetlands. Sea-level rise at the higher end also would increase coastal areas' exposure to storm waves, an unwelcome impact on a region already subject to flooding and erosion from tropical storms and hurricanes.

Alterations in temperature and precipitation are likely to significantly affect the region including the major economic sectors of agriculture and forests. Agriculture and forests are strongly influenced by changing stream flow, runoff, and soil moisture. Those changes in turn can affect the quality of both surface and ground waters. Present stresses on the water quality of the southeast seem to be associated with intense agricultural practice, urban development, coastal processes, and possibly mining activities. Under normal conditions, most regions of the Southeast do not experience significant water quality problems. However, as might be expected, the affects of those stresses on water quality occur more often during extreme conditions, particularly during dry weather, and water quality could become a serious concern for the region under changing climatic conditions.

Throughout the 20^th century, changes in the climate of the Southeast can best be characterized as geographically variable, showing some warming and some cooling as well as both increases and decreases in precipitation. The Southeast has been warming in recent decades, although there was an overall cooling of 2 to 3.5˚F during the 20^th century. Annual rainfall amounts increased 20-30% or more over some portions of the region, although other portions have experienced declines in rainfall amounts.

Most of the regional increases in precipitation have been the result of extreme events, downpours of 2 inches of rain in one day -- a tendency that could intensify in the Southeast and many other regions of our nation over the 21^st century. Such an increase in heavy and extreme precipitation is of concern because heavy rains are less efficient than moderate rainfalls in sustaining agriculture and replenishing water supplies; in addition, they are more likely to cause erosion and flooding, which are already problems in some areas. Strong seasonal and year-to-year variations in precipitation are seen in the Southeast, often as a result of strong El Niño-Southern Oscillation (ENSO) effects. El Niño events also tend to create atmospheric conditions that inhibit Atlantic tropical storm development, resulting in fewer hurricanes. La Niña events show the opposite effect, often allowing more hurricanes.

The largest warming during the last century has occurred along the coastal region (as much as 4ºF), with some inland cooling. Model scenarios project relatively uniform increases in annually averaged temperatures. However, the Canadian model projects increases that are twice as large as the Hadley model.

Observed precipitation changes during the last century are a patchwork of moderate increases and decreases. The Canadian model scenario for the 21st century indicates near neutral trends or modest increases, while the Hadley model projects increases of near 25% for the region.

Climate model results suggest that most parts of the Southeast, already our nation's warmest region, will become warmer in the 21^st century. Although model simulations do not agree on the amount of warming projected to occur, temperatures in the Southeast are projected to rise anywhere from 4 -- 10˚F. Much of this difference arises as a result of projections of different amounts of precipitation, with one model projecting a decrease in yearly precipitation, which leads to a relatively high increase in temperatures and the other suggesting a significant increase in precipitation (+~ 25%) and so less warming. One model of the El Niño - Southern Oscillation cycle suggests that the rainfall associated with El Niño and the intensity of droughts during La Niña phases might be intensified as atmospheric carbon dioxide increases.

Summer (above) and Winter (below) Climate Changes from Hadley Centre Scenarios Illustration of how the summer and winter climates in Georgia would shift under the Hadley climate scenario (HADCM2). For example, the summer climate in Georgia in the 2030s would be more like the current climate of the Florida panhandle. Source: NOAA, National Climatic Data Center.

Depending on the magnitude and seasonality of the changes, the projected increases in temperature and changes in precipitation could result in either increases in soil moisture or an increase in evapotranspiration (loss of water from soil and plants by both evaporation and transpiration) rates that would result in drying of soils. Any large increase in drying would further aggravate the water challenges facing some parts of the Southeast today. Because of the warm, humid climate that already characterizes the Southeast, the projected increase in temperatures and humidity would result in the Southeast experiencing a significant increase in the heat index (heat index is the combination of temperature and humidity).

The changes in the simulated heat index for the Southeast are the most dramatic in the nation with the Hadley model suggesting increases of 8 to 15ºF for the southern-most states, while the Canadian model projects increases above 20ºF for much of the region.