Laserfiche WebLink
0.9 <br />it 0.8 <br />0.7 <br />0.6 <br />co 0.5 <br />c <br />°_ 0.4 <br />m <br />2 0.3 <br />`o <br />U 0.2 <br />0.1 <br />Month <br />Figure 9: Region 25 — Yampa drainage correlation to water year streamflow at Craig, CO. <br />Figure 9 uses the same Palmer region 25 for the correlation with streamflow in the <br />Yampa basin measured at Craig, CO. In this basin, the 9 -month SPI in April has the best <br />correlation to water year streamflow. The 12 -month SPI also shows a good relationship <br />but with less lead time starting in May. Although the Palmer is not as strongly correlated <br />as the 9- and 12 -month SPI, it still shows a strong relationship with streamflow beginning <br />in April and peaking in June. It is unclear why the Palmer does not do as well for this <br />basin as it does for the others. <br />Recommendations <br />Although many studies have found the Palmer Drought Index problematic for a number <br />of statistical and physical reasons when comparing index values between climatically <br />diverse regions, this study shows clearly that when computed for relatively small climate <br />divisions using consistent input data, the Palmer Index relates surprisingly well to both <br />winter wheat yields and water year streamflow. It is recommended that the Palmer Index <br />be retained as a monitoring tool. Ongoing evaluation of where and when to use this index <br />should be investigated. The long memory of the Palmer Index (time scale of 9 -24 <br />months) means that it will not respond quickly to rapidly changing conditions so will not <br />be an ideal index in some situations. <br />The SPI is a very useful index that is easy to understand, straight forward to calculate and <br />relates directly to percentile rankings, which is how the majority of drought monitoring is <br />evaluated. It is recommended that both indices be calculated and that further <br />investigation is conducted to identify seasons, regions and time scales where each index <br />is most applicable. <br />o ° m` Q m <br />0 Q) a) n Q a��i <br />ca O o (D LL <br />z o U) <br />