Accurately measuring snowmelt -- an advance

NASA/Jet Propulsion Laboratory: … Thanks to new research from NASA's Jet Propulsion Laboratory (JPL), it is now easier to accurately track snowmelt -- water from snowpacks that melt in spring -- in mountainous regions.

…Snow cover is relatively easy to track using satellites that orbit Earth. But to piece together the water cycle in detail, scientists want to be able to measure snow water equivalent -- a quantity that describes the amount of water contained within the snowpack, or the depth of water that would be produced if the entire snowpack melted instantaneously -- over large areas and with high precision. Noah Molotch, a snow hydrologist at JPL, has combined data from NASA's Earth-observing satellites with a new mathematical snowmelt model to estimate snow water equivalent in the headwaters of the Rio Grande basin in Colorado's San Juan Mountains in the U.S. His technique can estimate the equivalent down to a scale of 100 meters (328 feet) over an area of 3,419 square kilometers (1,320 square miles) -- 10 times the area covered by previous snowmelt reconstruction techniques.

….Molotch's snowmelt model calculates the change in mass of the snowpack using three factors. First, the snow melting rate, which depends on solar radiation and air temperature. Second, the depletion rate of the snow-covered area, which is measured by NASA's Landsat-7 satellite and Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on board the Terra satellite. These missions take photos of Earth's continents and coastal regions. Third, the maximum snow water equivalent that has built up at the start of the melting season is calculated by adding up all of the predicted snowmelt over the time it takes to melt the snow in a given 100-meter (328-foot) "pixel."

Using this approach, Molotch shows that it is possible to track snow mass at new accuracy levels and over large mountain regions without needing to rely on measurements taken on the ground -- a major advantage. … Ultimately, the technique could make it possible to measure snowmelt and its contribution to the global water cycle in real time....

The headwaters of the Rio Grande upriver of the Del Norte gauging station. Intensive study areas are numbered 1-6. SNOTEL sites are denoted by white squares and National Weather Service Cooperative Observer meteorological stations are denoted by yellow diamonds. Map from the NASA/JPL website