Drought Triggers & Indices Index Doc

• Applicant: Colorado State University - Colorado Climate Center
• Grant Type: Non-Reimbursable
• Fiscal Year ‎(i.e. 2008)‎: 2009
• Project Name: Drought Triggers & Indices Evaluation and Role for Drought Mitigation & Response Plan
• CWCB Section: Water Conservation & Drought Planning
• Contract/PO #: OE PDA 10-71
• Grants - Doc Type: Supporting Documentation

Index Time Series Description
A full set of index time series, graphics and tables can be found in Appendix A.
The time series of Palmer and SPI indices were calculated for the period 1980 -2009.
Figure 3 shows the relationship of the Palmer Index to different time scale SPI indices.
This graph in no way implies that any one index is "better" than another. It simply shows
how well each SPI time scale correlates with the Palmer Index. It is important to note
that the Palmer is most highly correlated (depending on region) to the 12 and 24 month
time period suggesting that these indices are not very responsive to recent short wet
and /or dry periods. Longer time scales (12 months or more) tend to be best suited for
retrospective assessment of drought severity while shorter intervals may be better to point
out developing and worsening drought conditions.
Palmer Correlation to SPI Time Periods
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SPI Period
Figure 3: Palmer Index Correlation to SPI time scales by region.
Index Evaluation
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In an effort to characterize the utility of these indices for drought evaluation, independent
variables that relate to drought impacts were correlated with the indices. For the Eastern
Plains and Yampa/White basin, non - irrigated winter wheat yields were correlated to
monthly index values. Winter wheat (planted in the fall and harvested in early summer)
3 -month 6 -month 9 -month 12 -month 24 -month 48 -month