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COLORADO WATER SUPPLY CONDITIONS UPDATE FROM THE OFFICE OF THE STATE ENGINEER; DIVISION OF WATER RESOURCES August, 1991 ROOM 818,1313 SHERMAN ST.,DENVER,CO 80203; (303)-866-3581 JOHN R.KALISZEWSKI;EDITOR Statewide, water supplies diminished slightly in July as municipal and irrigation demands increased. However, except for isolated areas of the state conditions are near normal. Water supplies have generally been adequate. Periodic precipitation events have occurred at opportune times lessening irrigation demands. Conditions are much improved over one year ago in the Colorado and Yampa/White basins when these basins were classified as being in a moderate drought. Reservoir storage remains above average. Soil moisture conditions are generally much improved over last year's conditions. Water shortages, however, are likely to occur by late August in those areas of the state with less than adequate storage. Statewide precipitation for the month of July was 127%of average ranging from a low of 83%of average in the San Juan/Dolores basin to 203% of average in the Arkansas basin. Water year totals are slightly above normal across the state with the Rio Grande basin the highest at 125% of average and the South Platte basin the lowest at 93% of average. The statewide reservoir storage was 105%of average on August 1,which is 105%of last year's August 1 amount. The Gunnison basin continues to have the highest storage rate at 118%of average while the Rio Grande basin has the lowest storage rate at 90% of average. Statewide storage is currently 51% of capacity (approximately 9 million acre-feet). The National Weather Service 30 day forecast(starting August 1)for Colorado is for below average precipitation and above average temperatures. The 90 day forecast (starting August 1) is for above average precipitation and below average temperatures. Going into 1991,25%of the contiguous U.S.was experiencing drought conditions while 10%of the U.S.was experiencing extremely wet conditions. Drought conditions are expanding in the western U.S. while wet conditions are expanding in the eastern U.S. The Palmer index computed by the NOAA/USDA joint Agricultural Weather Facility identifies areas of prolonged abnormal dryness or wetness. The primary component evaluated is soil moisture. The index indicates extremely dry conditions occupying central and southern California,south central Washington,eastern Oregon,northeastern North Dakota, northwestern Minnesota, and the Colorado River basin in west central Colorado and east central Utah. Extremely wet conditions prevail in the upper midwest extending from southern South Dakota through Iowa, Illinois, and Indiana, and in the south central region of the U.S. including Louisiana, Arkansas, Mississippi, and Alabama. The Surface Water Supply Index (SWSI) developed by this office is used as an indicator of water supply conditions in the state. It is based on reservoir storage, streamflow, and precipitation for the summer period (May 1st through November 30). Weight factors are applied to each of the measured hydrologic factors in computing the SWSI values for each basin. During the summer period, streamflow is the primary component in each basin except the South Platte where reservoir storage is the primary component. The following SWSI values were computed for each of the seven basins on June 1, 1991 and 1990: August 1, 1991 Change From August 1, 1990 Basin SWSI Value July 1, 1991 SWSI Value South Platte +1.4 -0.3 +1.4 Arkansas +0.1 -0.4 +0.9 Rio Grande -0.1 -0.2 -0.7 Gunnison +0.8 -0.4 -1.4 Colorado +0.4 +0.2 -2.3 Yampa/White +0.0 -0.1 -2.2 San Juan/Dolores -0.9 -0.5 -1.0 SCALE -4 -3 -2 -1 0 +1 +2 +3 +4 Severe Moderate Near Normal Above Normal Abundant Drought Drought Supply Supply Supply 1