W. Slope melt-off may break records

Weaker snowpack, warmer weather contributing factors

Todd Hartman, Rocky Mountain News

Wednesday, May 16, 2007

Snowpack on Colorado's Western Slope is melting far faster than usual, with two river basins likely to melt off in near-record time, a federal scientist told water watchers Tuesday.

The status of western Colorado's snow is in marked contrast to conditions in the Denver region, where snowpack in the South Platte River basin stands at 104 percent of its May 15 average, as a stormy spring has reduced melting and kept water supplies bountiful.

The fast disappearance of snow west of the Continental Divide is likely in large part because of a weaker overall snowpack there, experts said. After a strong start to the snow season in late 2006, snowfall on the Western Slope dwindled.

"Any time we have less volume of snowpack to melt, the quicker it's going to reach zero," said Mike Gillespie, snow survey supervisor for the federal Natural Resources Conservation Service.

One scientist suggested the fast melt-off could be part of a broader trend, with snow melting earlier and stream flows rising sooner in springtime. One preliminary study in Colorado has found that snowmelt is now occurring two weeks earlier, on average, than in 1978.

"This year seems to follow the trend that we've been seeing over the past 30 years or so," said David Clow, a research hydrologist with the U.S. Geological Survey.

Clow said warmer springtime weather this year might be contributing.

"We can't say whether that's climate change or climate variability, but it is interesting and it does fit the pattern of global warming," he said.

One river basin, the Yampa-White in northwestern Colorado, is almost assuredly going to break its early melt-off record of June 7, Gillespie said. He predicts all the snow could be gone by next week.

The neighboring North Platte Basin is also going fast and on pace for a near-record melt.

Should the Western Slope experience average weather conditions in the next two weeks, two basins - the Yampa and the Gunnison - will be devoid of snow by June 1. Three other basins would be below 20 percent of average.

Such a melt-off would be far quicker than in a typical year, when snow usually remains well into June and sometimes July.

The fast melt-off isn't hurting the state's reservoirs, which are in the best shape in years, at 106 percent of average levels statewide.

Troubling trends

Scientists at Tuesday's joint meeting of the state's Water Availability Task Force and Flood Task Force delivered presentations on weather and climate. Several suggested that springtime is getting warmer in the state and the West. Among their data:

• For the past 21 years, state snowpack on May 1 has been below average three-fourths of the time.

• Springtime temperatures in the state's north-central mountains have been rising - 3.5 degrees since 1930. The temperature rise has been steeper since 1950.

• Snowmelt in Colorado is occurring about two weeks earlier, on average, since 1978.

• Streamflows across the West are rising earlier, corresponding to earlier snowmelt.

• Two river basins in western Colorado are on pace to melt off in record or near-record time.

hartmant@RockyMountainNews.com or 303-954-5048