From Aspen Journalism (Heather Sackett):

As a changing climate renders streamflow predictions less accurate, water managers are turning to new technologies for a clearer picture of what’s happening in their basin’s snowpack.

The city of Aspen last spring became the latest water provider in western Colorado to use remote-sensing lasers from airplanes to map the snowpack in the surrounding watershed. On April 7 and June 10, planes equipped with LiDAR, which stands for light detection and ranging, flew over the mountains surrounding Castle and Maroon creeks, measuring the depth of the snow and how much water it contained.

The snow from Castle and Maroon valleys eventually becomes Aspen’s municipal water supply as it trickles downstream. Knowing how much snow is left and where that snow is located can help Aspen’s water managers better plan for spring runoff.

“The information (that the flights) were able to share with us shows us so much information about where the snow collects and some of the runoff patterns,” said Margaret Medellin, the manager of Aspen’s Utilities Portfolio. “It’s a more sophisticated way of looking at the water content in our snow.”

The flights were conducted by NASA’s Airborne Snow Observatory, or ASO, an initiative co-founded by Jeffrey Deems, a research scientist at the National Snow and Ice Data Center at the University of Colorado where the data will be archived and distributed. Last month in Steamboat Springs, Deems gave a presentation on mapping mountain snowpack at Colorado Water Congress.

“It removes a good portion of the uncertainty,” Deems said in a separate interview. “The better we can manage the system, the more everybody benefits and is less in conflict.”

Streamflow forecasts — used by irrigators, water managers, federal and state agencies, and other entities — are based primarily on data collected from snow-telemetry, or SNOTEL, sites. These automated, remote sensors collect weather and snowpack information in Colorado’s mountainous watersheds.

But SNOTEL sites provide just a snapshot, often not telling the whole story, which leads to inaccurate streamflow forecasts.

When conditions at SNOTEL sites start to creep outside of “normal” historic data due to climate-warming effects — early-spring melting, dust on snow, warm winter temperatures, fires and beetle-kill — the forecasting models can begin to lose accuracy. By mapping an entire watershed, ASO flights paint a more complete picture of the state of the snow.

“As the past becomes less of a good guide to the future, we really need to know in greater precision and accuracy what the current state of the snowpack is,” Deems said. “The folks who are making the decisions on how to manage our water infrastructure — whether that’s a ditch, a dam or a headgate — they need the best forecast possible so they can make the correct decision at the right time.”

Avalanches and hydrology

The LiDAR mapping also has the potential to help water managers better understand extreme weather events such as the historic avalanche activity this past March. One of Deem’s LiDAR mapping photos showed mountain tops that were scoured and devoid of snow, and valleys and avalanche paths that contained deep piles — the result of huge avalanches. An unanswered question is whether this snow melted out sooner (because it slid to a lower elevation) or later (because avalanche debris is denser and more compact).

“It may actually have delayed melt into the runoff season,” Deems said. “It’s not something we can say definitively what the effect is, but for the first time, the data set may actually allow us to test that and get a better handle on how hydrology and avalanches interact.”

Denver Water, which provides water to 1.4 million people on the Front Range, last spring used ASO flights to see how much snow remained in the mountains surrounding Dillion Reservoir, its largest storage pool. Data from a June 24 flight showed that although the SNOTEL sites at about 11,000 feet were melted out, there was still 114,000 acre-feet of water in the snowpack above. Denver Water increased its outflows from Dillon Reservoir to make room for the coming snowmelt.

“That ended up being about half our seasonal runoff,” said Nathan Elder, Denver Water’s manager of water supply. “(ASO) is the next thing in snow measurement. We haven’t had an advancement like this since the late ’70s, when they started putting in SNOTEL sites.”

Costly technology

While innovative and useful, the technology is expensive. Over the past three years, the Colorado Water Conservation Board has spent $1.9 million on the Watershed Forecasting Partnership Program, with nearly $519,000 spent on ASO flights, according to Chris Arend, communications director for the Department of Natural Resources. The Castle and Maroon creek watersheds were mapped as an offshoot of a multiyear program in the Upper Gunnison River Basin.

A good approach, Deems said, would be for multiple local agencies to pitch in and share the cost, since each flight on the specially equipped plane can cost tens of thousands of dollars. For a small municipality such as Aspen, it’s just not worth it.

“It’s really hard to fund or justify funding big efforts like that,” Medellin said. “We are really excited about the data, but we have to think: Is this something we can really afford in this community? Right now, it seems like the benefit wouldn’t justify the costs.”

Editor’s note: Aspen Journalism collaborates with The Aspen Times on coverage of water and rivers. For more, go to aspenjournalism.com.

Note: Coyote Gulch caught up with Jeffrey Deems at the conference to ask him about measuring density or snow water equivalent. He told me that they get it from SNOTELs and that the technology will not replace them. In fact, he said that we need many more installed in the snow courses.