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COLORADO WATER SUPPLY CONDITIONS UPDATE PROM THE OFFICE OF THE STATE ENGINEER; DIVISION OF WATER RESOURCES January, 1991 ROOM 818,1313 SHERMAN ST.,DENVER,CO 80203; (303)-866-3581 JOHN R.KALISZEWSKI;EDITOR Colorado's water supplies are near normal. Conditions have improved considerably compared to conditions one year ago. Statewide precipitation was 84% of normal for the month of December with a high of 148% of normal in the Rio Grande basin and a low of 40% of normal in the Arkansas basin. Statewide precipitation totals for the water year (beginning October 1, 1990) are 109% of normal. The Soil Conservation Service reports that the statewide snowpack on January 1, 1991 was only 81% of average. However, it is 144%of the snowpack measured on January 1, 1990. Snowpack development is highest in the Rio Grande basin with 109% of normal and lowest in the Yampa/White basin with 71% of normal. Although it is still early in the season, nearly 40% of the seasonal snowpack is received by January 1 in an average year. The statewide reservoir storage is 111% of normal with a high of 141% of normal in the San Juan/Dolores basin and a low of 78% of normal in the Rio Grande basin. Streamflow statewide was below normal for the month of December due to abnormally cold temperatures resulting in low snowpack runoff. Approximately 80% of the annual streamflow in Colorado originates from snowpack runoff. The National Weather Service forecasts warmer and drier than average conditions for Colorado through March 1, 1991. While at this time last year the driest conditions were in the south and southwest sections of the state, this year the trend has reversed: The best prospects for near normal water conditions are in the Arkansas, Rio Grande, and San Juan/Dolores basins while the central and northern basins are currently forecast to have below normal runoff. The National Weather Service also advises that Colorado is a difficult region to develop long-range forecasts due to geographic diversity and a variety of weather patterns that impact Colorado conditions. Southern California is now in the fifth year of a drought and is growing increasingly dependent on excess flows in the Colorado River that Colorado is entitled to but is currently not using. The Colorado Climate Center at Colorado State University advised that a typical month of January in Colorado consists of abundant precipitation in the higher elevations and low precipitation in the lower elevations, especially the eastern plains. January is typically a major contributing month to the statewide snowpack water equivalency. However, over the last ten years, January has been abnormally dry despite the fact that the 1980's decade was overall very wet. 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, snowpack, and precipitation for the winter period (December 1 through May 1). Weight factors are applied to each of the measured hydrologic factors in computing the SWSI values for each basin. During the winter period, snowpack 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 January 1, 1991, and on January 1, 1990. January 1, 1991 January 1, 1990 Basin SWSI Value SWDI Value South Platte -0.6 -0.4 Arkansas +2.6 -0.1 Rio Grande +1.5 -3.4 Gunnison +0.2 -2.6 Colorado -0.3 -1.4 • Yampa/White +0.1 +1.5 San Juan/Dolores +0.2 -3.5 SCALE -4 -3 -2 ' -1 0 +1 +2 +3 +4 Severe , Moderate Near Normal Above Normal Abundant Drought Drought Supply Supply Supply 1