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• COLORADO WATER SUPPLY CONDITIONS UPDATE 1M THE OFFICE OF THE STATE ENGINEER; DIVISION OF WATER RESOURCES March, 1991 )M 818,1313 SHERMAN ST.,DENVER,CO 80203; (303)-866-3581 JOHN R.ICALISZE NSIU;EDITOR FLASH: Early March Storms Deliver Much Needed Snow To Central And Southwestern Colorado. February, 1991,will go down as one of the driest Februaries on record. Lack of new snow and unseasonably warm temperatures diminished the statewide snowpack to just 72% of average on March 1, 1991; however, it was 107% of last year's snowpack for that date. Snowpack development was highest in the Rio Grande Basin at 92% of average and lowest in the South Platte Basin at 61%of average. Low elevation precipitation for the month was only 59%of average with a high of 88%of average in the Arkansas Basin and a low of 22%in the South Platte Basin. Statewide precipitation (low elevation) totals for the water year (beginning October 1, 1990) are now 97% of normal. The statewide reservoir storage is 115% of average with a high of 152%of average in the Gunnison Basin and low of 85%of average in the Colorado Basin. Statewide streamflow was above average for the month due to the unseasonably warm temperatures and the resultant high snowpack runoff. Data collected by the U.S. Soil Conservation Service SNOTEL (SNOwTELemetry) on a daily basis of snowpack conditions statewide indicate that the early March storms provided significant amounts of snow in the central and southwest regions of the state. By March 7th, snowpack improvements (as a percentage of normal) were as follows: South Platte Basin +1% Arkansas Basin +8% Rio Grande Basin +15% Gunnison Basin +13% Colorado Basin +7% Yampa/White Basin +6% San Juan/Dolores +18% 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 March 1, 1991. March 1, 1991 Change from Basin SWSI Value Previous Month South Platte -1.3 -0.7 Arkansas -2.1 -1.2 Rio Grande -0.4 -1.3 Gunnison -1.2 -1.0 Colorado -2.1 -0.5 Yampa/White -2.3 -1.2 San Juan/Dolores -1.1 -0.8 SCALE -4 -3 -2 -1 0 +1 +2 +3 +4 Severe Moderate Near Normal Above Normal Abundant irought Drought Supply - Supply Supply 1