Dayton Daily News

To refine water forecasts, cities map snow by plane

- By Brittany Peterson

GUNNISON, COLO. — At a tiny airport surrounded by mountains, a three-person crew takes off for the inaugural flight above the headwaters of the Colorado River to measure the region’s snow by air.

Under the plane is a device that uses lasers, cameras and sensors to map snow and help drought-prone communitie­s improve forecasts of how much water will later fill reservoirs.

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 Conservanc­y District, one of Colorado’s largest water providers and the primary funder for the flight.

For decades, Western U.S. 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, snow at those sites — at around 9,000 feet above sea level — is melting earlier than normal and pushing water managers to look for other ways to finetune forecastin­g methods.

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

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

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

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

Others are working on ways to improve snow measuremen­ts too.

On the same day the plane scans the river’s headwaters, the U.S. Geological Survey is on the ground researchin­g an option that could be more affordable, even if it’s not as precise. The agency installed its own remote sensing stations above and below the typical elevation of SNOTEL sites and its laser-equipped drones measured the surroundin­g area.

Those results could take a couple of months to process since they’re still in the testing phase, said Suzanne Paschke, who is managing the project for USGS. The agency also paid for a segment of the headwaters snow mapping flight so it could cross-check its measuremen­ts.

Meanwhile, SNOTEL sites are also undergoing upgrades that could result in more accurate modeling, said Karl Wetlaufer, who helps run the program. In 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 elevations, where wind can whip snow around exposed mountainto­ps and make it hard to measure, Wetlaufer said.

The newer methods help fill in those data gaps at high elevations.

In June 2019, four SNOTEL stations showed snow had largely melted out in the Blue River basin, which feeds into the Dillon Reservoir that provides water to the Denver area. But mapping by Airborne Snow Observator­ies showed significan­t snow remained at higher elevations — giving water managers enough time to make room in the reservoir for the incoming runoff.

 ?? BRITTANY PETERSON / AP ?? A road winds through the Rocky Mountains. Some droughtpro­ne communitie­s in the U.S. West are mapping snow by air to refine their water forecasts.
BRITTANY PETERSON / AP A road winds through the Rocky Mountains. Some droughtpro­ne communitie­s in the U.S. West are mapping snow by air to refine their water forecasts.

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