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CU Boulder Researchers Report Nearly 5-degree Warming at Lake Dillon

January 13, 2019
A cyclist speeds past Summit County's Lake Dillon during day four of the 2016 Ride the Rockies race. Researchers at the University of Colorado have found that the reservoir's surface temperatures have risen 5 degrees Fahrenheit in the past 35 years.

A nearly four-decade water quality study led by a University of Colorado professor at Lake Dillon in Summit County has found that its surface temperature has warmed by almost 5 degrees Fahrenheit during that time.

Researchers at CU’s Cooperative Institute for Research in Environmental Sciences Center for Limnology have just published a study, launched in 1981, which concluded that the lake’s rapid warming and its lack of ecological response to that warming are explained by its high elevation.

“I was not surprised that the lake was warming,” said William Lewis, who is director of the CIRES Center for Limnology and lead author on a paper just published in the American Geophysical Union’s Water Resources Research. “But I was surprised at the rate of warming for the lake, as large as it is.”

Lake Dillon is well known to those who travel Interstate 70 across the Continental Divide, located on the south side of the interstate west of the Eisenhower Tunnel, and bordered by Frisco, Silverthorne and Dillon, its surface measured at just over 3,200 acres.

In an interview Friday Lewis said the average mean temperature during open water season during the 35-year study increased from 52.7 degrees Fahrenheit to 57.2 degrees.

Tracking the temperature change was not the main focus, but instead a byproduct of the study Lewis said, which was primarily targeting issues of water quality, because it is a reservoir serving customers of Denver Water.

Denver Water, Summit County and multiple government entities within the county, as well as the Colorado Department of Public Health and Environment, and also the Environmental Protection Agency, all have supported the study, Lewis said.

Lake Dillon is the highest lake yet studied for its full water column warming. It also is the first to analyze warming in a reservoir, as opposed to a natural lake.

Kevin Trenberth, a distinguished senior scientist at Boulder’s National Center for Atmospheric Research, whose work is focused on Earth’s energy imbalance and the heating of its oceans, said studies have shown that around the world, “Lake temperatures are warming more than the air temperatures. Of course, this often relates to how big and how deep the lake is.

“The bigger and deeper, the more likely it is to retain some of the cool, deep waters. This is not unique to Lake Dillon, but that’s a surprisingly large number.”

Lewis and his CIRES colleagues have collected detailed information on Lake Dillon’s temperature as well as its water quality and aquatic life. Full vertical profiles of the water temperature document changes in vertical distribution of heat over time, according to a news release. That record shows that warming of the tributary waters feeding Lake Dillon contributes to warming of its deepest waters.

While the warming of lakes in the tropics causes notable degradation in their water quality, the good news for Lake Dillon — and presumably similarly situated bodies of water — is that its health, due to both its latitude and high elevation, appears to be unaffected by its warming, for now, despite significantly increased human development in its watershed.

“It shows no response that we can detect, either physically or biologically, in response to this warming,” Lewis said. “This lake, and maybe other lakes located at very high elevation, show a certain amount of resistance to effects of climatic warming up to this point.”

While the significant warming at Lake Dillon is not currently a problem for its water quality or biological health, Lewis could make no promises, based on his research, about the future.

“It would be better if it didn’t warm a great deal more, but I can’t predict what the changes would be in the lake at progressively higher temperatures,” Lewis said.

“And that’s going to be a global phenomenon when it happens. It won’t be just this lake.”

Charlie Brennan: 303-473-1327, brennanc@dailycamera.com or twitter.com/chasbrennan

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