NASA To Map Snowpack Of Two Major Mountain Watersheds In Colorado And California
May 3, 2013

NASA To Map Snowpack Of Two Major Mountain Watersheds In Colorado And California

Alan McStravick for - Your Universe Online

In the very near future, the global issue surrounding the need for natural resources will shift from fossil fuels to fresh water. In preparation for this change of need, NASA has endeavored on a new airborne mission to create the first maps of the entire snowpack of two major mountain watersheds in California and Colorado. These western snow reserves, as they melt, provide greater than 75 percent of the total freshwater supply for the region.

The purpose of the NASAs Airborne Snow Observatory (ASO) mission is to generate an estimate of how much water is expected to flow out of these basins when the snow eventually melts. NASA contends the data-gathering technology could help to improve water management for upwards of 1.5 billion people worldwide whose very lives rely upon snowmelt for their water supply.

“The Airborne Snow Observatory is on the cutting edge of snow remote-sensing science,” Jared Entin, a program manager in the Earth Science Division at NASA Headquarters in Washington, said in a statement. “Decision makers like power companies and water managers now are receiving these data, which may have immediate economic benefits.”

This mission has been undertaken as a collaboration between NASA's Jet Propulsion Laboratory (JPL) and the California Department of Water Resources. NASA´s JPL is managed by Caltech in Pasadena.

The planned three year mission began in April of this year and includes weekly flights in NASA's Twin Otter aircraft over the Tuolumne River Basin in California´s Sierra Nevada. This particular region and its Hetch Hetchy Reservoir are the primary water supply for San Francisco. Additionally, the mission performs monthly flights over Colorado´s Uncompahgre River Basin. This watershed supplies water to much of the western United States. The weekly and monthly flights are slated to continue through the end of the snowmelt season, typically culminating in the month of July.

The mission's principal investigator, Tom Painter of JPL stated, “Changes in and pressure on snowmelt-dependent water systems are motivating water managers, governments and others to improve understanding of snow and its melt.” He continued, “The western United States and other regions face significant water resource challenges because of population growth and faster melt and runoff of snowpacks caused by climate change. NASAs Airborne Snow Observatory combines the best available technologies to provide precise, timely information for assessing snowpack volume and melt.”

The mission is utilizing two primary instruments in gathering measurements of the two properties most critical to understanding snowmelt runoff and timing. Those two properties had been mostly unmeasured until now.

Snow depth is measured through the use of a scanning lidar system obtained from the Canadian firm Optech Inc. It utilizes lasers to determine the first property, snow water equivalent. This property is represented as the amount of water in the snow on a mountain. Obtaining an accurate measurement of snow water equivalent is necessary for calculating the amount of water that will eventually runoff the mountain.

The second important instrument is an imaging spectrometer. The spectrometer is necessary for measuring the second integral property, known as snow albedo. Snow albedo represents the amount of sunlight reflected and absorbed by snow. Understanding this property helps in the prediction of the speed of snowmelt and determining the timing of its eventual runoff.

The mission seeks to combine these data, helping scientists to ascertain how changes in the absorption of sunlight can cause snowmelt rates to increase.

Flying within a 5,000-foot window between 17,500 and 22,000 feet, the ASO produces frequently updated mapping of the regions under investigation. Scientists will be able to use these maps to monitor changes over time. With each mission, data are processed and made available to participating water managers within 24 hours´ time. It has been determined the instrumentation used for the mission is able to calculate snow depth to within 4 inches and snow water equivalent to within five percent.

Prior to the ASO missions, estimates of snow water equivalent for the Sierra Nevada were extrapolated from a series of monthly manual ground snow surveys conducted between January and April. Among several limitations of this previous method were survey sites that were sparsely located in lower to middle elevations. Unmelted snow at higher elevations was never taken into account.

The necessity to get more accurate data is paramount as water managers use these survey data to forecast annual water supplies. Their decisions affect local water districts, agricultural interests and others. It has been noted the sparse sampling brought by survey site measurement leads to the possibility of large errors. The ASO mission, by contrast, is able to map all the snow throughout the entire snowmelt season.

“The Airborne Snow Observatory is providing California water managers the first near-real-time, comprehensive determination of basin-wide snow water equivalent,” stated Frank Gehrke, a mission co-investigator and chief of the California Cooperative Snow Surveys Program for the California Department of Water Resources. “Integrated into models, these data will enhance the state´s reservoir operations, permitting more efficient flood control, water supply management and hydroelectric power generation.”

Gehrke commented the lower and middle elevation manual surveys will continue while the results of the Airborne Snow Observatory data are incorporated into runoff models. “The snow surveys are relatively inexpensive, help validate observatory data and provide snow density measurements that are key to reducing errors in estimating snow water equivalent,” he concluded.

According to Painter, the ASO has plans to expand their mapping program to include the entire Upper Colorado River Basin and Sierra Nevada.

“We believe this is the future of water management in the Western United States,” he said.