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COLORADO WATER SUPPLY CONDITIONS UPDATE FROM THE OFFICE OF THE STATE ENGINEER; DIVISION OF WATER RESOURCES September, 1990 ROOM 818,1313 SHERMAN ST.,DENVER,CO 80203; (303)-866-3581 Statewide precipitation was slightly below normal for the month of August Precipitation averaged 84%of normal with a high of 127% of normal in the South Platte basin and a low of 47% of normal in the Yampa/White basin. These precipitation amounts are in contrast to the July conditions when statewide precipitation was 156% of normal. As is common in Colorado, precipitation varied considerably. August precipitation amounts were only 50% of normal in the extreme west-central and northwest sectors and in the immediate areas around Saguache, Walden, Lamar, La Junta, Springfield, and Colorado Springs. Precipitation in excess of 200% occurred in the immediate area between Fort Morgan and Akron, the area south of Trinidad,and the area northeast of Durango. Cumulative precipitation for the period October, 1989 through August, 1990 is 30% above normal for the Fort Morgan-Akron area and 30% below normal for the extreme northwest and west-central sectors of the state. In other areas of the state cumulative precipitation is near normal. Although reservoir storage has been drawn down considerably in the last 12 months, it still remains normal to above normal when compared to historic reservoir storage levels. Storage levels are slightly below normal in the Gunnison and Colorado basins. Relative storage remains highest in the Arkansas basin. The consumption of reservoir carry-over storage this year will impact conditions next year if the 1991 runoff is below normal and as a result storage cannot be replaced. The greatest impacts would be on recreational uses of water. Streamflow at key index gaging stations approached twenty year lows in the Gunnison and Yampa/White basins. Soil moisture deficiency (as measured by the Palmer Drought index) has developed to serious levels in the west-central and northwest sectors of the state. September precipitation tends to be more uniformly distributed across the state than at any other time of the year. However, since the atmosphere in September is still relatively warm, it can hold large amounts of water vapor and can produce very heavy rains. 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 1 through December 1). Weight factors are applied to each of the measured hydrologic factors in computing the SWSI values. 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 September 1, 1990. September 1 Change from Basin SWSI Value August 1, 1990 South Platte +2.1 +0.7 Arkansas +0.5 -0.4 Rio Grande -0.4 +0.3 Gunnison -2.6 -1.2 Colorado -1.9 +0.4 Yampa/White -3.5 -1.3 San Juan/Dolores -0.7 +0.3 SCALE -4 -3 -2 -1 0 +1 +2 +3 +4 Severe Moderate Near Normal Above Normal Abundant Drought Drought Supply Supply Supply 1