SUSCEPTIBILITY OF RESERVOIRS TO DROUGHT USING PALMER INDEX

The Palmer index is a widely used indicator of meteorological drought derived from estimates of moisture deficiency that is computed monthly for 344 climate divisions in the contiguous United States. While not often used to predict hydrologic drought, a comparison of the Palmer i ndex, precipitation deficit, and annual runoff for selected geographic regions and droughts shows a correlation in water deficiency for each indicator. Using the Palmer index for the period 1895-1989, a nationa l and regional assessment of 516 Corps of Engineers reservoirs shows a significant regional variation in drought duration, reservoir storage capacity, and reservoir purposes. When severe or extreme droughts are analyzed, 87% of the reservoirs with multiple- purpose storage capaci ty are in climate divisions where the duration is less than 36 consecu tive months. When mild-to-moderate droughts are included, durations of over 120 consecutive months are found in some areas of Colorado, Mont ana, Wyoming, and North Dakota. National and regional assessments, usi ng the Palmer index, are useful for analyzing reservoirs and droughts over large geographic regions; however, they are limited in their usef ulness for improving the planning and operation of individual reservoi rs for drought. For this task, computer simulation is necessary.