According to Climate Center, Recent Storms are Drought-Easing, Not Drought-Ending: State Behind in Reservoir Storage and Accumulations

Amid varying reports of Colorado’s current drought situation and water supply outlook following the March blizzard of 2003, climatologists at Colorado State University’s Colorado Climate Center stress that recent rain and snowfall, although beneficial in easing the state’s drought, are not enough to end the state’s drought. The climate researchers add that, even with a wetter than average spring, it is not likely that Colorado will pull out of long-term drought impacts in 2003, and that the state will continue to face serious irrigation and municipal water shortages throughout the spring and summer.

Roger Pielke Sr., Colorado’s state climatologist and director of the Colorado Climate Center, indicates that, although the current drought is not the worst in Colorado’s history in terms of precipitation, it has been severe in terms of its impact on irrigation and municipal water resources because of the state’s large demand on water. He encourages water managers and citizens to continue plans for ongoing conservation efforts.

"The short-term impact of the recent blizzard and the precipitation last week are significant in helping both spring crops and grazing conditions, delaying the onset of fire season, permitting improved river flow in the spring runoff and increasing water supply in the reservoirs," said Pielke. "However, it is not enough to pull Colorado out of the longer-term impacts of the drought in terms of water supply. Also, not all parts of the state benefited as much from the blizzard and rain."

In mid-February, snowpack was approximately 75 percent of average statewide. As of April 1, according to the Natural Resources Conservation Service, snowpack is 94 percent of average statewide and 177 percent of last year’s snowpack for this date. Perhaps more important, according to the Climate Center, is that snowpack statewide is currently 91 percent of the average seasonal peak accumulations, or the average maximum for the year, which generally occurs on April 13. Therefore, Colorado’s mountains need to not only maintain the snowpack they have but also receive a significant amount of precipitation within the next few weeks to gain the additional 9 percent of snowpack needed to truly get the state back to its average snowpack.

The April 1 percent of average seasonal peak snow water equivalent accumulations for Colorado river basins, and average date this occurs, based on preliminary data as compiled by the Natural Resource Conservation Service are:

• Arkansas – 103 percent of average, which on average occurs on April 12;
• Colorado – 97 percent of average, which on average occurs on April 7;
• Gunnison – 86 percent of average, which on average occurs on April 12;
• North Platte – 92 percent of average, which on average occurs on April 25;
• Rio Grande – 76 percent of average, which on average occurs on April 13;
• San Juan, Animas, Dolores and San Miguel – 72 percent of average, which on average occurs on April 8;
• South Platte – 102 percent of average, which on average occurs on April 24;
• Yampa & White – 87 percent of average, which on average occurs on April 16.
• The moisture is very beneficial and will go a long way in easing Colorado’s drought," said Climate Center climatologist Nolan Doesken. "However, we are so far behind in terms of water supply, it would take several storms of the magnitude of the recent blizzard to build up enough snowpack to fill Colorado’s reservoirs. It would likely take well above-average precipitation for the next two to four years to get water supply levels back to normal."

Pielke explains that some of the confusion regarding snowpack and water supply stems from the way snowpack numbers have been reported. Snowpack and precipitation percentages for Colorado’s water supply basins are generally given with respect to a particular date. With warm, dry weather, for example, 100 percent with respect to this week’s average snowpack could be at 90 percent with respect to next week’s average. Additionally, he explains, 100 percent of average compares the current snowpack to a multi-year average but does not consider other conditions, such as dry soils that can reduce runoff or current reservoir storage levels.

"Due to last summer’s drought conditions, the soil is very dry, deeper ground water is reduced and water storage reservoirs are well below average. Therefore, a significant portion of the melt from this year’s snowpack will be absorbed into the ground and into ground water before beginning to fill depleted reservoirs," said Pielke. "It will take more than average snowpack to produce average runoff into reservoirs, and much more than an average snowpack to fill the depleted reservoirs to average levels."

Other climate and weather experts agree. According to NOAA’s U.S. Drought Outlook, recent storms greatly improved water supply prospects in Colorado’s basins. However, the report states that the odds for significant change in the status of the long-term drought decline as the snow season wanes, and their forecast is for limited improvement.

According to the Natural Resources Conservation Service, many locations from central Colorado received more liquid equivalent precipitation from the recent blizzard than was recorded from October through early March. However, despite some enormous totals, many locations’ season-to-date snowfall totals are still only near or below average; expert consensus indicates that the storm will reduce but not come close to eliminating drought and water supply concerns in Colorado.

Some forecasters are calling for a wetter than average spring, which could further reduce drought impacts to Colorado. Pielke stresses that although this is good news, communities and citizens should not make policy decisions at the local, state and national level based solely on climate and weather predictions. Instead, he advises that citizens need to understand that Colorado is a semi-arid state that has a large population and high water-usage demand. The state should address long-term infrastructure and usage issues, such as improved water use efficiency, that will reduce water demand.

According to the climatologists, Coloradans still should prepare for widespread water restrictions this spring and summer. Exactly what and how severe the restrictions will be depends in part on what happens in April.

"March and April have large impacts on Colorado’s water supply in northeastern Colorado. March was above average," said Pielke. "The spring months for this part of the state in 2002 were warm and dry. Certainly by late April, we will have a very good indication of where we stand going into the summer for the Front Range urban communities."

The Colorado Climate Center, housed in Colorado State University’s Department of Atmospheric Science, provides information and expertise on weather and climate patterns for the state of Colorado. Through its threefold program of climate monitoring, climate research and climate services, the center provides Colorado climate information on the Web at http://ccc.atmos.colostate.edu and in Colorado Climate magazine, which is available through subscription. The web site has a special section dedicated to drought.