Topographic control of snow distribution in an alpine watershed of western Canada inferred from spatially-filtered MODIS snow products

J Tong,P L Jackson,S J Déry

doi:10.5194/hess-13-319-2009

J Tong, P L Jackson + Show 1 more

Open Access

https://doi.org/10.5194/hess-13-319-2009

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Abstract

Abstract. A spatial filter (SF) is used to reduce cloud coverage in Moderate Resolution Imaging Spectroradiometer (MODIS) 8-day maximum snow cover extent products (MOD10A2) from 2000–2007, which are obtained from MODIS daily snow cover extent products (MOD10A1), to assess the topographic control on snow cover fraction (SCF) and snow cover duration (SCD) in the Quesnel River Basin (QRB) of British Columbia, Canada. Results show that the SF reduces cloud coverage and improves by 2% the accuracy of snow mapping in the QRB. The new product developed using the SF method shows larger SCF and longer SCD than MOD10A2, with higher altitudes experiencing longer snow cover and perennial snow above 2500 m. The gradient of SCF with elevation (d(SCF)/dz) during the snowmelt season is 8% (100 m)−1. The average ablation rates of SCF are similar for different 100 m elevation bands at about 5.5% (8 days)−1 for altitudes <1500 m with decreasing values with elevation to near 0% (8 days)−1 for altitudes >2500 m. Different combinations of slopes and aspects also affect the SCF with a maximum difference of 20.9% at a given time. Correlation coefficients between SCD and elevation attain 0.96 (p<0.001). Mean gradients of SCD with elevation are 3.8, 4.3, and 11.6 days (100 m)−1 for the snow onset season, snowmelt season, and entire year, respectively. The SF decreases the standard deviations of SCDs compared to MOD10A2 with a maximum difference near 0.6 day, 0.9 day, and 1.0 day for the snow onset season, snowmelt season, and entire year, respectively.

Highlights

Snow plays a vital role in the energy and water budgets of drainage basins in northern British Columbia (BC) and many other mountainous regions
The spatial filter (SF) increases snow cover fraction (SCF) in the Quesnel River Basin (QRB) with maxima of 5.3%, 8.9%, 13.5%, 13.7%, and 15.6% in the elevation bands of 2500 m, respectively
Even at altitudes ≤1000 m, the method indicates about 2.5% snow cover in summer, an unrealistic feature of the Moderate Resolution Imaging Spectroradiometer (MODIS) data that may be attributed to the presence of fog, shadowing effects, and/or low illumination in valleys or on shaded slopes in mountainous terrain (Riggs and Hall, personal communication, 2008)

Summary

Introduction

Snow plays a vital role in the energy and water budgets of drainage basins in northern British Columbia (BC) and many other mountainous regions. Snowmelt contributes up to 90% of the annual runoff in high elevation basins of the Rocky Mountains, United States (Schmugge et al, 2002). Snow supplies large amounts of water for human consumption (Barnett et al, 2005). The heterogeneous distribution of snow cover at the local to regional scale arises from variability in meteorological (precipitation, temperature, radiation and wind), topographical (elevation, slope, and aspect), and vegetative controls, among others. Elevation is often presumed to be the dominant factor affecting snow cover distribution.

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