The ABC's of snowmelt: a topographically factorized energy component snowmelt model

Because of the crucial role snowmelt plays in many watersheds around the wo rld, it is important to understand and accurately quantify the melt process . As such, numerous mathematical models attempting to describe and predict snowmelt have arisen. There are two main categories of models: conceptual i ndex models and more intricate energy balance models. The index models, lik e the degree-day or radiation index models, are practical enough for use in large basins for operational purposes; while the energy balance models, th ough they are complicated and require large amounts of data, can represent the physics behind melt and give more accurate representations of the spati al distribution of melt within small research basins. The ABC model present ed here attempts to bridge the gap between these two extremes by providing a simple yet physically justifiable method that uses elevation and radiatio n indices together with some measurements to distribute melt over a watersh ed. This new model separates the energy that causes snowmelt into three com ponents: a spatially uniform component, a component that is proportional to elevation, and one that is proportional to solar illumination (which is de termined by topography). Measurements of snowmelt;It several topographicall y unique points (called 'index points') in a watershed are related to eleva tion and solar illumination through regression in order to factor the melt energy into the three separate components at each time step. The model is d riven using inputs from snowmelt measurements at the index locations used t o calibrate the regression at each time step. Then the spatial patterns of solar illumination and elevation are used to predict the spatial distributi on of melt over the whole watershed. Field data supplemented with synthetic ally generated data is used to test the model. Copyright (C) 1999 John Wile y & Sons, Ltd.