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June 1996 OD30U3 COLORADO WATER 3. Colorado Rearranged Severe Drought An artificial scenario is formed by taking the flows in Scenario I and assuming they occur in decreasing order so that the lo".test flows come at the end. It is characterized by a 16-year mean flow of9,6 mafand has a return period from 2,000 to 10,000 years or more. This scenario is designed to discover how the system would respond to a truly catastrophic drought. This scenario was the "representative drought" that served as the basis for the study, APPROACH The tirst component of the study W3S, for each year of rhe representative drought. to predict overall nalive flows and then to break these down into water availabilities as key locations in the Basin. Concurrently, socia-economic conditions in the region for future decades were projected. The analysis assumes a drought would begin at the time of lhe study's commencement -- 1990, These hydrologic and socio- economic projections provide the basis for the study's impact assessment and the institutional analyses. /\ 7 The second component was a legal and institutional assessment, designed to identify and investigate alternative legal and organizational arrangements that could be used [0 increase capacity for preparing for and coping with SSD. The third component was to estimate damages or impacts from droughts on economic sectors (including both instream and offstream beneficiaries), on social considerations. and on (he environment. These three components were then incorporated into (\\'0 complementary types of interdisciplinary modeling assessment studies: A computer optimizmion that evaluates economic impacts on inslream and offstream water us~rs of allt:rnative policy instrumenls; and A dynamic "gaming" phase, an interactive computer program designed to represent impacts of policies chosen in real time by players representing various basin interests. IMPACTS OF A SEVERE, SUSTAINED DROUGHT Findings, conclusions and recommendations derive largely from computer simulations of the behavior of the physical- institutional water management system when subjected to the stress of a 38-year severe drought. a drought resembling one which occurred late in the 16th century, The findings, conclusions and recommendations fall into three groups: Those which penain to the existing operating rules (the Law of the River); Those which penain to potential changes in the existing rules; and Those which penain to the feasibility of making such changes (through negotiation, legislation, or litigation). DROUGHT PERFORMANCE OF THE LA W OF THE RIVER The SSD hydrologic models predict that, under present institutional arrangements (the Law of the River), Lake Powell and other major Upper Basin reservoirs would be emptied, and Lake Mead nearly so, after two decades of severely reduced runoff. Water deliveries for consumptive uses in the Upper Basin would fall to about half of normal levels, albeit for only a few years. Consumptive uses in the Lower Basin would be largely unaffected, save for those served by the Central Arizona Project Until recently, California was able to use about a million acre- feet of Colorado River water annually beyond its regular compact entitlements, After the completion of the Central Arizona Project canal, such "surplus" usage is unlikely to recur reliably, and chronic inability to divert this surplus as .a, .. drought-caused shonage is not included, In all, basinwide shortages would be less than 25 percent of normal demands, even at the depth of the drought. California, in its recent droughts. has coped with more severe shonages. So-called instream. or non consumptive, water uses by the lower basin (hydroelectric power generation, water-based recreation, environmental protection and salinity control) would fare less well. Predicted power generation declined during the low-flow years and would cease altogether at the depth of the drought. Water-based recreation at Lakes Mead and Powell and at five other system reservoirs would decline with decreasing water levels in those reservoirs (see Fig, 3, next page), Instream flows would be inadequate at times for the survival of some endangered species at some locations. Riparian wetlands would be seriously affected, Salinity levels in drinking and irrigation water would rise to levels higher than experienced since the completion of Hoover Dam. The single largest predicted economic impact of the drought was the loss of electricity, with an average value of$600 million annually, Reductions in water deliveries to municipal, industrial and agricultural users would also be substantial, and benefits to those users would be significantly reduced due to salinity increases. I' , Recreational benefits would fall by lesser but still appreciable amounts. Lower Basin states would experience minimal losses to consumptive water uses but would suffer major losses to non consumptive uses.