FLOOD10416

• County: Statewide
• Title: Historical Perspectives on Colorado Drought
• Date: 12/1/2003
• Prepared For: CWCB
• Prepared By: HDR
• Floodplain - Doc Type: Educational/Technical/Reference Information

Historical Perspectives on Colorado Drought

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Colorado Water Conservation Board
Dry Periods by River Basin
Based on the 24.month Standard Precipitation Index

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Figure 20. Plot 01 drought severity by year lor malor Colorado River Basins based on 24.month
Standard Precipitation Index (created by ewes. Stanton and Busto, 1997).

Figure 20 was prepared by the Colomdo Water Conservation and presents the periods
of moderate. severe, and extreme drought by basin since the latc 1800s. The figure
shows that major droughts rarely impact all or Colorado's major river basins
simultaneously. When they do. as noted in the 1890s. the 1930s, the 19505 and the
1970s, the impacts are significant. On the other hand. many regIOnal droughts occur
almost every decade that impact only one or two basins for periods of one to two
years.

Drought is a very frequent visitor to Colorado. Single season droughts with
precipitation of75% or less of average for one to three months in a row occur nearly
every year in Colorado. Based on long-tenn weather station records. it ,,,'as observed
that at least 5% of the state is experiencing drought on J- to 24-month timesca1es
almost all of the time (McKee el al. 2000).

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t>.-1any drought observers insist that drought cycles exist. Some suggest thai
sunspot cycle of II years or a "double sun spot cycle" of 22 years controls
Colorado's drought patterns. Others claim that a J- or 7-year cycle exists in

3I'lIund. comos aruund.

Druught cyclos: what

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