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<br />.' --.:- ~ <br /> <br />OOlj1, t.? <br />......L::.... ...... <br /> <br />THE 1990 DROUGHT-AN ILLUSTRATED HISTORY <br /> <br />Portions of the West experienced a fourth year of drought in 1990, Low moisture <br />conditions were evident based upon the indices, or measurement tools, used to assess <br />drought. Although many indices demonstrate water supply conditions, each index <br />measures a different factor, <br /> <br />Due to climate variables and water storage development in the Western United <br />States, no single index can reflect all of the variables needed to measure drought, <br />This chapter contains illustrations to demonstrate five different indices, Taken <br />together, they show the growth or decline of drought in 1990, related to Bureau of <br />Reclamation projects, <br /> <br />In the West, water storage in manmade reservoirs changes the natural water cycle, <br />The amount of water that remains from one year to the next in those reservoirs may <br />change the water supply picture, This carryover storage tends to mask the severity <br />of drought until consecutive dry years lead to reservoir storage depletion. However, <br />to assess the total water supply picture, the following indices are helpful: the Palmer <br />Drought Severity Index, winter snowpack, streamflow forecasts, accumulated <br />reservoir inflow, and reservoir storage supply, The remainder of this chapter <br />illustrates these index measurements, <br /> <br />13 <br />