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2025 Hazard Mitigation Plan <br />Kittitas County, Washington <br />. ln contrast with other natural hazards, the impact of drought is less obvious and may spread over <br />a larger geographic area. These characteristics have hindered many governments'preparation of <br />drought contingency or mitigation plans. <br />Snowpack is critical to Washington's water supply. Approximately three (3) quarters of the runoff from <br />the Cascades originates as snowpack. This snowpack acts as a natural reservoir, and a weak snowpack <br />during the winter months or a shift in the timing of snowmelt can impact water supply in the spring and <br />summer. Some basins located in the lower elevations are more rain dominant, and spring precipitation is <br />important for filling up soil moisture before the summer dry period develops...101 <br />4.6.3.2. HazardLocation <br />A drought can occur anywhere in the Kittitas County region and affect the entire planning area. <br />4.6.3.3. Hazard ExtenUlntensity <br />Many drought indices have been developed; however, the Palmer Drought Severity lndex (PDSI) is the <br />most prominent index of meteorological drought utilized in the United States for drought monitoring. PDSI <br />uses readily available temperature and precipitation data to estimate relative dryness to indicate the <br />prolonged and abnormal moisture deficiency or excess. As an important climatological tool, the PDSI <br />assists in evaluating the scope, severity, and frequency of prolonged periods of abnormally dry or wet <br />weather. Furthermore, it can be utilized to identify disaster areas and indicate the availability of irrigation <br />water supplies, reservoir levels, range conditions, amount of stock water and potential intensity of <br />wildfires. -102'.103 <br />The PDSI is a standardized measure that compares moisture deficiency and excess on a numericalscale <br />that usually ranges from positive five (5) to a negative five (5). Positive values mean there is an excess <br />in moisture supplies and conversely, negative values indicate moisture demands in excess of supplies. <br />Tabfe 4-41 displays the PDSI categories and Figure 4-7 illustrates the drought conditions in the <br />contiguous United States as measured by the PDSI for the month of June 2023...104 <br />Table 4-41. Palmer Drought Severity lndex <br />101 National lntegrated Drought lnformation System. (n.d.). Drought.gov: Washington. Retrieved from <br />https ://www.d rouq ht.qov/states/wash inqton. <br />102 National Weather Service, Climate Prediction Center. (2005). Drought lndices: Explanation. Retrieved from <br />https://www.cpc.ncep.noaa.qov/products/analvsis monitoring/cdus/palmer_drouqhVwpdanote.shtml. <br />103 National Center for Atmospheric Research. (n.d.). Climate Data Guide: Palmer Drought Severity lndex (PDSI) <br />Retrieved from https://climatedataquide.ucar.edu/climate-data/palmer-drouqht-severitv-index-pdsi. <br />10a National Centers for Environmental lnformation. (2023). Historical Palmer Drought lndices: Maps. Retrieved <br />from https://www.ncei.noaa.qov/access/monitorinq/historical-palmers/maps/psi/202312. <br />Extreme Drought <br />Severe Drought <br />Moderate Drought <br />- 1.99 to + 1.99 Mid-Range <br />Moderately Moist <br />Very Moist <br />Extremely Moist <br />Palmer Drought <br />Severity lndex <br />- 4.00 and below <br />Category <br />l'lr,lr:, ill:):r: <br />Chapter 4: Hazard ldentification and Risk Assessment 97