Modelling snow melt and snowcover depletion in a small alpine cirque, Canadian Rocky Mountains

Abstract

AbstractSpatial and temporal patterns of areal snowcover depletion (SCD) were studied over a small (<0·6 km2) alpine cirque within the Canadian Rocky Mountains using a combined approach of daily acquisition of remotely sensed imagery, together with meteorological observations and snowmelt modelling. Digital terrestrial photographs were georeferenced using a novel software tool together with a high‐resolution digital elevation model and used to derive measurements of fractional snowcovered area (SCA) over the cirque. Manual snow surveys carried out in the pre‐melt period were used to describe the initial frequency distribution of snow water equivalent (SWE) values over the cirque, and indicated a lognormal distribution of SWE when surveys were stratified by terrain features. Rates of snowmelt were simulated using a physically based snowmelt energy balance model, Snobal, driven by observed meteorological conditions at a nearby station, which were adjusted for slope orientation and exposure by making corrections to observed incoming shortwave and longwave radiation components in the cold regions hydrological model platform. Simulated melt rates were then applied to the approximated SWE distributions to model the decline in SCA over the spring. The model was found to perform well for the simulation of snowmelt based on point observations of SWE at the meteorological station, and produced a close correspondence between simulated and observed SCD curves representing two opposing slopes within the cirque. The results show that both the pre‐melt distributions of SWE and the spring melt rates exhibit considerable spatial variability between distinct slope units within the cirque, and that this variability has a significant impact on simulated SCD. Assuming a unimodal pre‐melt frequency distribution and conditions of spatially uniform snowmelt over complex terrain such as this can lead to large errors in the simulation results. It is suggested that modelling applications intended to represent snowmelt dynamics and areal SCD in similar alpine environments consider the effects of spatial variation in SWE distribution and melt energetics between slopes. Copyright © 2009 John Wiley & Sons, Ltd.