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(National Drought Mitigation Center, 2003). The direct and indirect costs of drought total more than $9 billion per year in the United States. The worst drought (36% of U.S.) in recent history occurred in July 1988, and the NCDC reports the estimated cost as $40 billion (National Drought Mitigation Center, 2010). According to a report by the National Oceanic Atmospheric Administration (NOAA), a full 33% of the contiguous United States spent 2012 in the grip of a severe to extreme drought – "severe" and "extreme" are NOAA's most serious official classifications on the drought scale. Risk Assessment. Indian River County overall, has a moderate vulnerability to the impacts from drought due to the County's large agricultural land tax base. The western area of the County is most vulnerable to the impacts of drought because this area is extensively involved in farming and ranching. As of 2017, the average annual market value of agricultural products in Indian River County was $145 million (www.agcensus.usda.gov). The urbanized communities along the County's coast are less vulnerable due to their location and non-agricultural economic base. Potential impacts to Indian River County's potable water supply during drought conditions appear to be slight. The Palmer Drought Index has become the semi-official drought index. It is most effective in determining long term drought—a matter of several months—and is not as good with short-term forecasts (a matter of weeks). It uses a 0 as normal, and drought is shown in terms of minus numbers; for example, minus 2 is moderate drought, minus 3 is severe drought, and minus 4 is extreme drought. The Palmer Index can also reflect excess rain using a corresponding level reflected by plus figures; i.e., 0 is normal, plus 2 is moderate rainfall, etc. Another reference tool is the Keetch-Byram drought index (KBDI), which is a continuous reference scale for estimating the dryness of the soil and duff layers. The index increases for each day without rain (the amount of increase depends on the daily high temperature) and decreases when it rains. The scale ranges from 0 (no moisture deficit) to 800 (prime drought condition). The range of the index is determined by assuming that there is 8 inches of moisture in a saturated soil that is Indian River County Comprehensive Emergency Management Plan Basic Page 53