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COLORADO <br /> WATER SUPPLY CONDITIONS UPDATE <br /> FROM THE OFFICE OF THE STATE ENGINEER; DIVISION OF WATER RESOURCES September, 1991 <br /> ROOM 818,1313 SHERMAN ST.,DENVER,CO 80203; (303)-866-3581 <br /> JOHN R.ICALISZEWSKI;EDITOR. <br /> Statewide,water supplies diminished slightly in August as municipal and irrigation demands increased. However, <br /> except for isolated areas of the state conditions are near normal. Water supplies have generally been adequate. Periodic <br /> precipitation events have occurred at opportune times lessening irrigation demands. Conditions are much improved over <br /> one year ago in the Gunnison and Yampa/White basins when these basins were classified as being in a moderate drought. <br /> Reservoir storage remains above average. Soil moisture conditions are generally much improved over last year's conditions. <br /> Statewide precipitation for the month of August was 121% of average ranging from a low of 83% of average in the <br /> Gunnison basin to 163%of average in the Arkansas basin. Water year totals are slightly above normal across the state with <br /> the Rio Grande basin the highest at 122%of average and the South Platte basin the lowest at 99%of average. The statewide <br /> reservoir storage was 107% of average on September 1, which is 105%of last year's September 1 amount. The Gunnison <br /> basin continues to have the highest storage rate at 115%of average while the Rio Grande basin has the lowest storage rate <br /> at 93% of average. Statewide storage is currently 49% of capacity (approximately 9 million acre-feet). <br /> The National Weather Service 30 day forecast(starting September 1) for Colorado is for above average precipitation <br /> and above average temperatures. The 90 day forecast (starting September 1) is for above average precipitation and below <br /> average temperatures.The Office of the State Climatologist,at Colorado State University,advises that there is no correlation <br /> between summer weather patterns and winter weather patterns. As such, the wet summer of 1991 does not suggest that <br /> the winter of 1991-92 will be anything but normal. Climatologists across the world are closely monitoring two phenomena: <br /> El Nino,the South Pacific ocean current,and the active Philippines volcano,Mount Pinatubo.To date,temperature anomalies <br /> of the El Nino current are relatively insignificant. However, if these anomalies strengthen as expected, the results in the <br /> Western U.S. are likely to be a significant departure from normal. This could be either exceptionally wet or exceptionally <br /> dry. The last time El Nino effects were felt,in 1988, conditions in the western U.S. were dry. Climatologists are also <br /> concerned that the extraordinary amounts of volcanic ash spewed into the atmosphere by Mount Pinatubo could alter <br /> • weather patterns. <br /> The Surface Water Supply Index (SWSI) developed by this office is used as an indicator of water supply conditions <br /> in the state. It is based on reservoir storage, stream flow, and precipitation for the summer period (May 1st through <br /> November 30). Weight factors are applied to each of the measured hydrologic factors in computing the SWSI values for each <br /> basin. During the summer period, streamfiow is the primary component in each basin except the South Platte where <br /> reservoir storage is the primary component. The following SWSI values were computed for each of the seven basins on <br /> September 1, 1991 and 1990: <br /> Sept. 1, 1991 Change From Sept. 1, 1990 <br /> Basin SWSI Value Aug. 1, 1991 SWSI Value <br /> South Platte +3.0 +1.6 +2.1 <br /> Arkansas -0.2 -0.3 +0.5 <br /> Rio Grande -0.1 0.0 -0.4 <br /> Gunnison +0.1 -0.7 -2.6 <br /> Colorado -0.3 -0.7 -1.9 <br /> Yampa/White +0.1 +0.1 -3.5 <br /> San Juan/Dolores -0.6 +0.3 -1.7 <br /> SCALE <br /> -4 -3 -2 -1 0 +1 +2 +3 +4 <br /> Severe Moderate Near Normal Above Normal Abundant <br /> Drought Drought Supply Supply Supply <br /> 1 <br />