The ABCs of Snowmelt: A Topographically Factorized
Energy Component Snowmelt Model
Kevin S. Williams1 and David G. Tarboton2
Because of the crucial role snowmelt plays in many watersheds around the world, it is important to
understand and accurately quantify the melt process. As such, numerous mathematical models at-
tempting to describe and predict snowmelt have arisen. There are two main categories of models:
conceptual index models and more intricate energy balance models. The index models, like the
degree-day or radiation index models, are practical enough for use in large basins for operational
purposes; the energy balance models, though they are complicated and require large amounts of
data, can represent the physics behind melt and give more accurate representations of the spatial
distribution of melt within small research basins. The ABC model presented here attempts to bridge
the gap between these two extremes by providing a simple yet physically justifiable method that
uses elevation and radiation indices together with some measurements to distribute melt over a
watershed. This new model separates the energy that causes snowmelt into three components: a
spatially uniform component, a component that is proportional to elevation, and one that is propor-
tional to solar illumination (which is determined by topography). Measurements of snowmelt at
several topographically unique points in a watershed are related to elevation and solar illumination
through regression in order to factor the melt energy into the three separate components at each
time step. Then the spatial patterns of solar illumination and elevation are used together with these
regressions to determine the spatial distribution of melt over the whole watershed. Field data sup-
plemented with synthetically generated data are used to test the model.
1Utah
Division of Water Resources, 1594 West North Temple Suite 310, Salt Lake City, Utah
84114-6201 USA
2Civil and Environmental Engineering, Utah State University, Logan, Utah 84322-4110 USA
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