Application of a New Temperature-Index Model to Glaciers of the Bow River Basin, Eastern Canadian Rockies

Alberta’s Bow River, which is a water source for several population centers including the City of Calgary and surrounding agricultural land, has its headwaters in the glaciated eastern slopes of the Canadian Rockies. The combined effects of rapid glacial retreat in the Canadian Rockies, higher drought frequency, and increased demand are likely to heighten water stress in Southern Alberta in the future. However, there has been little focus to date on the extent and importance of glacial meltwater in the Bow River. The Bow River basin contains 74.5 km2 of glacier ice, which amounts to only 0.29% of the basin. While this number is not high compared to some glacierized areas, Hopkinson and Young (1998) report that in dry years, glacier melt can provide up to 50% of late summer flows at a station in the upper reaches of the river system. To better understand glacial contributions to the entire basin, an improved temperature index model was developed to predict glacial melt. Based on previous work by Anslow (2004) and Pellicotti et al (2005), the model combines solar radiation and temperature in a unique way to predict runoff. The improved model draws more heavily on physical processes than traditional temperature index models, which is preferable for models run at regional and local scales. The performance of the model is equivalent to that of traditional temperature index models at our calibration site, with an adjusted R2 of 0.59 for both the traditional model and the new radiation-temperature melt model. Application of the model in the Bow River Basin shows total summer glacier runoff to be highly variable between 2002 and 2010. Two thirds of total summer glacier runoff is contributed by melting ice, rather than winter snow pack. Monthly runoff is highest in early to mid-August, when maximum summer temperatures and lowest surface albedo values are seen on the glacier. Future research will examine historical runoff contributions between 1950 and 2010, as well as the impact of ongoing glacial retreat on the glacier contributions to Bow River discharge.