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Table 3 <br />Palmer Drought Severity Index Classifications <br />PDSI Value Classification <br />4.00 or more Extremel wet <br />3.00 to 3.99 Very wet <br />2.00 to 2.99 Moderately wet <br />1.00 to 1.99 Slightly wet <br />0.50 to 0.99 Incipient wet spell <br />0.49 to -0.49 Normal <br />-0.50 to -0.99 Incipient drought <br />-1.00 to -1.99 Mild drou ht <br />-2.00 to -2.99 Moderate drought <br />-3.00 to -3.99 Severe drou ht <br />-4.00 or less Extreme drought <br />The National Climatic Data Center (NCDC) has developed an archive of monthly PDSI <br />values from 1895 to present for every climate division of the United States. Within <br />Colorado, there are five NCDC climate divisions, with Division 4 corresponding to the <br />South Platte River basin. Monthly PDSI values for the South Platte River basin, over the <br />last 105 years are presented on Figure 6. <br />Figure 6 <br />Palmer Drought Severity Index <br />NCDC Colorado Division 4 -South Platte Basin <br />10 <br />8 <br />6 <br />4 <br />10-Year <br />Average <br />~ 2 <br />0 <br />a <br />~ 0 <br />t <br />o -2 <br />-4 <br />-6 <br />-8 <br />-10 ' <br />rn °0 0 o in o <br />00 d) d) d) d) ~ <br />N ~ M ~ V ll~ U ~ ~ ~ ~ W W ~ ~ O <br />d) d) d) d) d) d) d) d) d) d) d) d) d) d) d) O <br />Year <br />Page 12 of 21 <br />