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CHAPTER 9. DROUGHT <br />9-3 <br />Plan, Kittitas County has experienced serious or extreme drought conditions 10 to 15 percent of the time <br />from 1895 to 1995, and meets the criteria to be categorized as one of nine counties that are the most at-risk <br />for drought. The total social and economic impacts of these events on the Kittitas County planning area are <br />not known at this time. <br />9.2.2 Location <br />The National Oceanic and Atmospheric Administration (NOAA) has developed several indices to measure <br />drought impacts and severity and to map their extent and locations: <br />– Palmer Z Index: measures short-term drought on a monthly scale. Figure 9-1 shows this index <br />for July 2018. <br />– Palmer Drought Severity Index (PDSI): attempts to measure the duration and intensity of the <br />long-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 patterns plus <br />the cumulative patterns of previous months. Since weather patterns can change almost literally <br />overnight from a long-term drought pattern to a long-term wet pattern, the PDSI can respond <br />fairly rapidly. Figure 9-2 shows this index for July 2018. <br />– Palmer Modified Drought Index: Operational version of the Palmer Drought Severity Index. <br />Figure 9-3 shows this index for July 2018. <br />– Palmer Hydrological Drought Index: measures hydrological impacts of drought (e.g., <br />reservoir levels, groundwater levels, etc.) which take longer to develop and longer to recover <br />from. This long-term drought index was developed to quantify these hydrological effects, and <br />it responds more slowly to changing conditions than the PDSI. Figure 9-4 shows this index for <br />July 2018. <br /> <br /> <br />Figure 9-1. Palmer Z-Index for July 2018