FIGURE 2-1 Percent area of the United States in severe and extreme drought, January 1985-July 2005.

SOURCE: Based on data from the National Climatic Data Center/NOAA.

significance and a high priority is placed on water resources management. Some water shortages can be the result of overappropriation of supply so that “drought” occurs even in years of “normal” precipitation.

On average approximately 15 percent of the United States is affected by drought each year, based on the historical record from 1895 to now (National Climatic Data Center/NOAA, 2005). Figure 2-1 illustrates recent drought trends. Figure 2-2 illustrates longer-term trends for one location and shows a number of periods noteworthy for their duration, severity, and spatial extent.

A still ongoing drought began in 1996 for large parts of the country. Approximately 35 to 40 percent of the country has been affected at one time or another by severe to extreme drought during this period, and for some regions drought conditions have persisted for five or more years. For example, parts of the Southeast, particularly Georgia, North Carolina, South Carolina, and Florida, experienced three to four consecutive years of drought between 1999 and 2002. In the West much of the Southwest experienced five consecutive years of drought between 2001 and 2004, while much of Montana, Idaho, and surrounding states have experienced severe drought for as many as seven consecutive years since 1999. The most recent drought is particularly notable in that it was hotter than a similar drought of the 1950s. In general, western North America has seen significant warming over the last 100 years, particularly in the last couple of decades.

The recent period of unprecedented population increase in the western United States coincided with one of the wettest periods on record. During the

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