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COLORADO <br /> WATER SUPPLY CONDITIONS UPDATE <br /> FROM THE OFFICE OF THE STATE ENGINEER; DIVISION OP WATER RESOURCE December, 1990 <br /> ROOM 818,1313 SHERMAN ST.,DENVER,CO 80203; (303)-866-3581 <br /> JOHN R.KALISZEWSIG;EDITOR <br /> Colorado's water supplies are near normal. Conditions have improved considerably compared to one year ago. <br /> Statewide precipitation was near normal for the month of November averaging 102% of normal with a high of 134% of <br /> normal in the Arkansas basin and a low of 89% of normal in the South Platte basin. The Soil Conservation Service <br /> reports that the statewide snowpack on December 1, 1990 was only 69%of average. However, it is 158%of the snowpack <br /> measured on December 1, 1989. Snowpack development is highest in the Rio Grande and South Platte basins with 94% <br /> of normal and lowest in the Yampa\White basin with 44% of normal. Although it is still early in the season, nearly 20% <br /> of the seasonal snowpack is received by December 1 in an average year. The statewide reservoir storage is 102% of <br /> average with a high of 120% of normal in the Arkansas basin and a low of 73% of normal in the Rio Grande basin. <br /> Streamflow statewide was normal to above normal for the month of November due to abnormally warm temperatures and <br /> resultant snowpack runoff. <br /> The National Weather Service forecasts warmer and drier than average conditions for Colorado through March 1, <br /> 1991. The National Weather Service also advises that Colorado is a difficult region to develop long-range forecasts due <br /> to geographic diversity and a variety of weather patterns that impact Colorado conditions. Southern California is now in <br /> the fifth year of a drought and is growing increasingly dependent on excess flows in the Colorado River that Colorado is <br /> entitled to but is currently not using. <br /> The Colorado Climate Center at Colorado State University advised that a typical month of December in Colorado <br /> consists of abundant precipitation in the higher elevations and low precipitation in the lower elevations, especially the <br /> eastern plains. The Center recently completed a study under the direction of State Climatologist, Dr. Tom McKee, relative <br /> to the variability of snowpack development in the northern United States Rocky Mountain region including Colorado,Utah, <br /> Montana, Wyoming, and Idaho. Within Colorado itself there is a significant degree of variation in April 1 snowpack <br /> conditions on an annual basis. A high degree of variability exists in the San Juan basin and across the Front Range. <br /> Lower variability exists in the central and north central regions of Colorado including South Park, Middle Park, and North <br /> 0 Park. Mountain ranges that face predominantly south and southwest have high variability while north and northwest <br /> trending ranges have typically a more stable snowpack development. A particularly significant phenomenon that was found <br /> suggests long-term cycles (multidecadenal) of wet or dry conditions in the north half of the study area (Wyoming,Montana <br /> and Idaho) and opposite conditions in the south half of the study area (Utah and Colorado). Since the early 1970's the <br /> southern section has been wet while the northern section has been dry. <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, snowpack, and precipitation for the winter period (December 1 through May <br /> 1). Weight factors are applied to each of the measured hydrologic factors in computing the SWSI values. During the <br /> winter period, Snowpack is the primary component in each basin except the South Platte where reservoir storage is the <br /> primary component. The following SWSI values were computed for each of the seven basins on December 1, 1990, and <br /> on December 1, 1989. <br /> December 1, 1990 December 1, 1989 <br /> Basin SWSI Value SWDI Value <br /> South Platte -0.9 -1.9 <br /> Arkansas +1.4 -2.5 <br /> Rio Grande -0.1 -3.3 <br /> Gunnison +0.8 -2.5 <br /> Colorado -0.7 -2.1 <br /> Yampa/White +0.4 -1.5 <br /> San Juan/Dolores +0.7 -2.8 <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 />