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I I I I I I I I I I I I I I I I I I I Table 5. Classes for wet and dry periods of drought (after Palmer, 1965) Monthly Index Value Class More than 4.00 Extremely wet 3.00 to 3.99 Very wet 2.00 to 2.99 Moderately wet 1.00 to 1.99 Slightly wet 0.50 to 0.99 Incipient wet spell 0.49 to -0.49 Near normal -0.50 to -0.99 Incipient drought -1.00 to -1.99 Mild drought -2.00 to -2.99 Moderate drought -3.00 to -3.99 Severe drought Less than -4.00 Extreme drought 15 Drought Severity Drought Severity is indicated by the length-of-time the drought continues, the water deficit (shown as negative PDSI index values) and by the areal extent of the drought conditions. The PDSI for the Uinta Basin Climatological Division is presented in Figure 8 for the period 1895 through July of 1990. Figures for Utah's other climatological divisions can be found in Appendix A These figures graphically show several droughts that have affected the Utah area. It is of interest to examine drought conditions in the Uinta Basin for the period 1895-1990, in terms of length- of-drought and water deficit (negative values). The drought of 1899 through 1906 appears to be the most severe, lasting 7 years with index values as low as -5 in 1900. The early 1930's showed drought conditions in the Basin as did the 1953-1965 period and the mid-1970's. The period 1979 through 1988, with the exception of a 3-month moderate drought during the summer of 1981, has been near normal to very wet. With the lack of fall and early winter snow in October 1988, the Uinta Basin fell into a moderate drought. By March and April of 1989, the Basin began to feel the effects of severe drought. That drought continues through the fall of 1990. The indication of the severity of drought is also reflected by the length-of-time the area continues in drought conditions. That is, the longer the drought conditions persist, the more precipitation is required to pull the area out of drought. Table 6, calculated for September 1990, shows the precipitation necessary to return each climatic division to near normal conditions.