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Figure 1 Periods of drought in western Nebraska, five or more years in duration, 12001960. Periods of drought shown in black. Numbers in parentheses following year indicate length of drought period. Average duration of drought: 12.8 years (adapted from Weakly, 1965).

1895 1905 1915 1925 1 935 1945 1955 1965 1975 1985 1995

Year

Figure 2 Percent area of the Great Plains experiencing severe to extreme drought, 18951995.

1895 1905 1915 1925 1 935 1945 1955 1965 1975 1985 1995

Year

Figure 2 Percent area of the Great Plains experiencing severe to extreme drought, 18951995.

tively, of the region in severe and extreme drought. Second, it is rare for severe drought not to be occurring at some location in the region in every single year during 1895 to 1995. Third, clusters of drought years, while rare, are particularly noticeable in the 1930s, mid-1950s, late 1970s, and late 1980s to early 1990s. Multiyear droughts are important because impacts magnify as drought continues into a second and subsequent years. As surface and subsurface water supplies are gradually depleted, more economic sectors are affected. It often takes years for these systems (i.e., reservoirs, groundwater) to recover following an extended drought episode.

Figure 3 illustrates the percent area of three river basins in the Great Plains region in severe to extreme drought during the period 1895 to 1995. The river basins shown are the Missouri, Arkansas-White-Red, and Rio Grande. These three basins encompass most of the area of the Great Plains. The drought climatology of these three basins displays characteristics similar to those shown in Figure 2. However, there are two important differences. First, largely because of the spatial characteristics of drought, it is more common for drought to affect nearly 100% of these basins. This is especially noticeable for the Arkansas-White-Red and Rio Grande basins. This information is important to planners and water supply managers. Second, the pattern of drought differs from one portion of the region to another. For example, the 1930s drought was of much greater duration in the Missouri Basin than in the Rio Grande. By contrast, the 1950s drought was of greater duration and intensity in the Rio Grande basin. This illustrates the regional nature of drought and the fact that planning must be based on the drought of record for the area of interest. Tree-ring data can help scientists reconstruct the long-term climatic history of the region.

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