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COLORADO - WATER SUPPLY CONDITIONS UPDATE FROM THE OFFICE OF THE STATE ENGINEER; DIVISION OF WATER RESOURCES October, 1991 ROOM$13,I313 SHEnMAN ST.,DEWIER.CO WW2; (303)-066.3581 JOHN R.XAIJSZEWSIC;EDR'OR Statewide, water supplies improved in September as municipal and irrigation demands decreased. Except for isolated areas of the state,conditions are normal to significantly above normal. Water supplies have generally been adequate. Periodic precipitation events have occurred at opportune times lessening irrigation demands. Conditions are improved over one year ago in the Yampa/White basin when this basin was classified as being in a moderate drought Steamflows increased significantly in the Rio Grande and San Juan/Dolores basins as a result of reduced demand and above normal precipitation. Reservoir storage remains above average. Soil moisture conditions have diminished due to the abnormally warm and dry conditions that have prevailed. Statewide precipitation for the month of September was 114%of average ranging from a low of 87%of average in the South Platte basin to 167%of average in the San Juan/Dolores basin. Water year totals are slightly above normal across the state with the Rio Grande basin the highest at 124%of average and the South Platte basin the lowest at 98%of average. The statewide Teservoir storage was 108% of average on October 1,which is 106% of last year's October 1 amount. The Gunnison basin continues to have the highest storage rate at 115%of average while the Rio Grande basin has the lowest storage rate at 91%of average. Statewide storage is currently 51%of capacity (approximately 9 million acre-feet). The National Weather Service 30 day forecast (starting October 1) for Colorado is for normal precipitation except for the Arkansas basin which is forecast to have below average precipitation,with statewide temperatures to remain above normal. The 90 day forecast (starting October 1) is for above average precipitation and below average temperatures. The Pacific Northwest reports extremely dry conditions with negligible precipitation measured in the Seattle area since September 1, 1991. Abnormally hot temperatures in Southern California have increased demand while diminiching water supplies. It is too early to determine whether or not these conditions are the result of the South Pacific ocean current, El Nino, or the effects of volcanic ash spewed into the atmosphere by Mount Pinatubo in the Philippines. The Surface Water Supply Index(SWSI) developed by this office is used as an indicator of water supply conditions • the state. It is based on reservoir storage, stream flow, and precipitation for the summer period (May 1st through vember 30). Weight factors are applied to each of the measured hydrologic factors in computing the SWSI values for each basin. During the summer period, streamfiow 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 October 1 , 1991 and 1990: October 1, 1991 Change From October 1, 1990 Basin SWSI Value Seut.1. 1991 SWSI Value South Platte +2.1 -0.9 +2.1 Arkansas -0.3 -0.1 -0.1 Rio Grande +2.6 +2.7 0.0 Gunnison -1.5 -1.6 -1.9 Colorado +1.3 +1.6 -0.6 Yampa/White -0.7 -0.8 -2.7 San Juan/Dolores +3.2 +3.8 +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 •