|The Instrumental Record
Varying Patterns of 20th Century Drought
Each drought in the 20th century has a unique signature. The timing and evolution of droughts, and the areas impacted are variable, making it difficult to understand just what causes drought onset and persistence. Although the central High Plains appears to be the region most often affected by the most persistent droughts, the southern Plains, and parts of Texas in particular, appear to suffer from the highest frequency of drought. However, evidence from the instrumental record indicates that drought can affect any region of the U.S.
The graphic to the right illustrates four regional droughts. Each graph shows the variations in the instrumental Palmer Drought Severity Index (PDSI) from 1895-1995 for each of the four regions; northern California, eastern New York, northwestern Texas, and north-central Nebraska (graphs are based on a grid point within each region). The accompanying maps show the spatial pattern of drought for key drought years.
The drought of the late 1980s to early 1990 is highlighted in the top graph. This drought affected northern California, and is not evident in the other graphs of PDSI for other regions. The top map shows the spatial pattern of drought in 1992, depicting the northwestern U.S. as the focus of this drought. This drought was the most persistent period of drought in this region on record.
The second graph shows the PDSI values for eastern New York, highlighting the 1960s drought. The map to the right, for 1965, displays the coverage of the drought in the eastern United States. Although the western Unites States experienced wet conditions in 1965, this year was one of the years contributing to the worst drought on record for eastern New York.
The 1950s drought was centered in the southern Plains, as is illustrated in the third graph for northwestern Texas. The 1950s drought was the most severe drought in the 20th century for this area, impacting much of the southern and central U.S. The map above shows the drought in 1953.
The bottom graphs displays PSDI for north-central Nebraska and illustrates the severity of the 1930s drought in this area. The accompanying map shows the spatial extent of drought in 1937.
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