(Photo: Philip Fortnam)

Researchers Improve Methods to Measure Snowpack

Snow might be one of the ways to differentiate the sensibilities of hydrologists from others not sharing their professional interest. Whereas non-hydrologists may see the photo at right as a lovely snow scene hydrologists viewing the winter landscape may think of the problems of measuring snowpack to determine spring runoff.

With the Southwest and most of the West in the throes of a prolonged dry spell, water resource managers have an even greater need for accurate water availability estimates. Obtaining these estimates depend on the availability of more precise measurement of snowpack. What falls as snow this season later flows as a vital water supply. In fact, spring flow and other surface waters make up 54 percent of Arizona’s water supply.

The main problem with measuring snowpack in the West is that snow falls over a great expanse of territory, with much of it in inaccessible alpine areas. The stations for measuring the snow are too few and far between to adequately cover the expanse. Further, snow in different areas yield different amounts of runoff or what is called snow water equivalent (SWE), depending upon such variables as soil moisture, slope and snow composition. A consideration of these variables is important when working out SWE estimates.

Work is being done by researchers Roger Bales and Noah Molotch of the University of Arizona’s Climate Assessment for the Southwest (CLIMAS) and researchers from the Southwest Regional Earth Science Application Center to improve methods for estimating SWE across the West. This would lead to greater accuracy in estimating water availability throughout the year.

The method involves interpreting satellite imagery to determine the snow-covered area on the land surface and integrating the information with ground-based estimates of SWE. The method enables researchers to estimate SWE over an entire river basin or more extensive land surface and assimilate the estimates into hydrologic models. A process-based methodology is applied that takes into account basin-wide snowfall patterns, elevation, terrain, local hydrology, solar radiation, air temperature, soil composition and other physical factors affecting total SWE.

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