Saturday, March 25, 2023

Western cities map wind-to-snow to refine water forecast

Gunnison, Colo. ( Associated Press) — At a small airport surrounded by mountains, a three-person crew takes off for the inaugural flight over the headwaters of the Colorado River to measure the area’s snow by air.

Underneath the plane is an instrument that uses lasers, cameras and sensors to map the ice and help drought-prone communities predict how much water will fill the reservoirs later.

The method, developed nearly a decade ago at NASA’s Jet Propulsion Laboratory, is “the gold standard of snow measurement,” said Emily Carbone of the Northern Colorado Water Conservation District, one of Colorado’s largest water providers and the primary funder for the flight.

For decades, western US states have been measuring snow through hundreds of remote sensing sites known as SNOTEL stations, which are operated by the federal Natural Resources Conservation Service. But as climate change causes rising temperatures, the ice in those places — about 9,000 feet above sea level — is melting earlier than normal and prompting water managers to look for other ways to improve forecasting. Still working.

Among the options is a method of aerial snow mapping, which gives accurate snow measurements across the basin.

The Airborne Snow Observatories flight in mid-April measured the area around the headwaters of the Colorado River. But the hope is to expand work along the strained river, which 40 million people rely on, said company co-founder Jeffrey Deems.

Removing the uncertainty in one of the data points “could be important in a water-stressed region,” said Paul Miller, a hydrologist at the Colorado Basin River Forecast Center.

But Miller also noted the limitations of aerial snow mapping, which can cost thousands of dollars or more per flight and only provide measurements for the day you fly. The technique also doesn’t account for variables such as air temperature and late storms that can affect water supplies.

Others are also working on ways to improve snow measurements.

As aircraft scan the upper reaches of the river, the US Geological Survey is researching an alternative that may be more economical, even if not as accurate. The agency set up its own remote sensing stations above and below typical heights of SNOTEL sites, and its laser-equipped drones measured the surrounding area.

Suzanne Paschke, who manages the project for the USGS, said those results could take a few months to process because they are still in the testing phase. The agency also paid for a segment of the Headwaters Snow Mapping flight so that it could cross-check its measurements.

Meanwhile, SNOTEL sites are also undergoing upgrades, which could result in more accurate modelling, said Carl Wetlaufer, who helps run the program. In the coming years, the federal agency plans to expand the number of sites that include sensors for solar radiation, wind and soil moisture. But the stations still can’t be moved to higher altitudes, where wind can hit the ice around exposed mountains and make it difficult to measure, Wetlaufer said.

New methods help fill in those data gaps at high altitudes.

In June 2019, four SNOTEL stations showed that ice had largely melted in the Blue River Basin, which drains into the Dillon Reservoir that supplies water to the Denver area. But mapping by the Airborne Snow Observatories has shown that significant snow remains at high altitudes – giving water managers enough time to make room in the reservoir for oncoming runoff.

Taylor Winchell, climate adaptation strategist at Denver Water, said, “That information allowed us to prepare for another peak of runoff and to accurately deplete our reservoirs to capture that water and avoid any effects of flooding.” “

The incident and other success stories of California water managers, who had been using the technology for many years, led to the formation of a coalition of Colorado water agencies, nonprofits, and local governments to advance more snow mapping flights. inspired.

“We think it’s worth it to get more valuable and detailed information, but we can’t afford to fly as often as we want,” said Northern Water’s Emily Carbone, who is leading the group.

The group developed a plan to seek external funding for the flights and in March received a grant from the Colorado Water Conservation Board to help cover some of the costs.

After her agency’s first snow mapping flight over the headwaters of the Colorado River last month, Carbone was eager to get her hands on the results.

The data indicated that as of mid-April, there was 369,000 acre-feet of water stored in ice over reservoirs at the head of the Colorado River. Since this was the first time that the region’s ice was mapped from the wind, there are no historical trends to compare. Carbone is still working to calculate how much of it can make it into the reservoir.

Northern Water launched another flight over the same area in May to find out how much ice has melted since the April flight and how efficient it is at moving to reservoirs.

“We have a lot to learn but it’s good to get this data and get a better picture of what’s really happening in our basin snowpack,” she said.


The Associated Press receives support from the Walton Family Foundation for its coverage of water and environmental policy. Associated Press is solely responsible for all content. For all of Associated Press’s environmental coverage, visit go to


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