Interrelationships among Snow Distribution, Snowmelt, and Snow Cover Depletion: Implications for Atmospheric, Hydrologic, and Ecologic Modeling

Abstract

Local, regional, and global atmospheric, hydrologic, and ecologic models used to simulate weather, climate, land surface moisture, and vegetation processes all commonly represent their computational domains by a collection of finite areas or grid cells. Within each of these cells three fundamental features are required to describe the evolution of seasonal snow cover from the end of winter through spring melt. These three features are 1) the within-grid snow water equivalent (SWE) distribution, 2) the gridcell melt rate, and 3) the within-grid depletion of snow-covered area. This paper defines the exact mathematical interrelationships among these three features and demonstrates how knowledge of any two of them allows generation of the third. During snowmelt, the spatially variable subgrid SWE depth distribution is largely responsible for the patchy mosaic of snow and vegetation that develops as the snow melts. Applying the melt rate to the within-grid snow distribution leads to the exposure of vegetation, and the subgrid-scale vegetation exposure influences the snowmelt rate and the grid-averaged surface fluxes. By using the developed interrelationships, the fundamental subgrid-scale features of the seasonal snow cover evolution and the associated energy and moisture fluxes can be simulated using a combination of remote sensing products that define the snow-covered area evolution and a submodel that appropriately handles the snowmelt computation. Alternatively, knowledge of the subgrid SWE distribution can be used as a substitute for the snow-covered area information.