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Figure 5 <br />Comparison of Selected Indicator Stations <br />z,soo,ooo <br />2,000,000 <br />1,500,000 <br />1,000,000 <br />3 <br />O <br />LL <br />500,000 <br />* A dashed line indicates that data is projected on the secondary Y-axis. <br />~ ~ I~ I 1 <br />~' <br />~ I~ ~ ~ ~\ kit ~='"~. ! ,r 1 I ~\ l,\ ,\ <br />~\ vl 4,~-r l ~~A~ ! ~ I , OYI ~JJ \ <br />,y <br />v 1~~ <br />o~ o~ o~ o~ o~ o <br />o <br />o <br />r r r r r r r r r r N <br />180,000 <br />160,000 <br />140,000 <br />120,000 <br />100,000 <br />80,000 <br />60,000 <br />40,000 <br />20,000 <br />North Platte River Near Northgate - 06620000 Cache La Poudre River at Mouth of Canyon Near Fort Collins- 06752000 <br />South Platte River at Julesburg - 06764000 - - Cherry Creek Near Franktown' - 06712000 <br />~~ North Fork South Platte River below Geneva Creek at Grant' - 06706000 Middle Boulder Creek at Nederland' - 06725500 <br />- ~ Big Thompson River at Mouth of Canyon Near Drake'- 06738000 <br />Climate Considerations <br />0 <br />LL <br />The principal climate parameters influencing water supply and demand are precipitation <br />and temperature. The Palmer Drought Severity Index (PDSI) was developed (Palmer, <br />W.C., 1965) to combine these parameters in a standardized method for the purpose of <br />describing moisture conditions without the influence of reservoir storage, imports, or <br />major diversions. The PDSI attempts to measure the duration and intensity of the long- <br />term drought-inducing circulation patterns. Long-term drought is cumulative, so the <br />intensity of drought during the current month is dependent on the current weather <br />patterns plus the cumulative patterns of previous months. Since weather patterns can <br />change almost literally overnight from along-term drought pattern to a long-term wet <br />pattern, the PDSI can respond fairly rapidly. <br />The PDSI is a monthly value (index) that indicates the severity of a wet or dry spell. This <br />index is based on the principles of a balance between moisture supply and demand. Man- <br />made changes were not considered in this calculation. The index generally ranges from <br />-6 to +6, with negative values denoting dry spells and positive values indicating wet <br />spells. The PDSI Index classification is presented in Table 3. <br />Page 11 of 21 <br />