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<br /> <br />2021 Multijurisdictional Local Hazard Mitigation Plan <br /> <br /> The hydrological impacts of drought (e.g., reservoir levels, groundwater levels, etc.) take longer to <br />develop and it takes longer to recover from them. The Palmer Hydrological Drought Index quantifies <br />long-term hydrological effects. It responds more slowly to changing conditions than the Palmer Drought <br />Index. <br /> While the Palmer indices consider precipitation, evapotranspiration and runoff, the Standardized <br />Precipitation Index considers only precipitation. In the Standardized Precipitation Index, an index of zero <br />indicates the median precipitation amount; the index is negative for drought and positive for wet <br />conditions. The Standardized Precipitation Index is computed for time scales ranging from one month to <br />24 months. <br />Figure 9-1 shows examples of these indices as of early June 2021. <br /> <br />U.S. Drought Monitor <br />The U.S. Drought Monitor (USDM) is a map that is updated weekly to show the location and intensity of drought <br />across the country. The USDM uses a five-category system: <br /> D0—Abnormally Dry <br /> Short-term dryness slowing planting, growth of crops <br /> Some lingering water deficits <br /> Pastures or crops not fully recovered <br /> D1—Moderate Drought <br /> Some damage to crops, pastures <br /> Some water shortages developing <br /> Voluntary water-use restrictions requested <br /> D2—Severe Drought <br /> Crop or pasture loss likely <br /> Water shortages common <br /> Water restrictions imposed <br /> D3—Extreme Drought <br /> Major crop/pasture losses <br /> Widespread water shortages or restrictions <br /> D4—Exceptional Drought <br /> Exceptional and widespread crop/pasture losses <br /> Shortages of water creating water emergencies <br /> <br />The USDM categories show experts’ assessments of conditions related to drought. These experts check variables <br />including temperature, soil moisture, water levels in streams and lakes, snow cover, and meltwater runoff. They <br />also check whether areas are showing drought impacts such as water shortages and business interruptions. <br />Associated statistics show what proportion of various geographic areas are in each category of dryness or drought, <br />and how many people are affected. U.S. Drought Monitor data goes back to 2000. <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />9-2