Abstract
Abstract. Glacier melt provides important contributions to streamflow in many mountainous regions. Hydrologic model calibration in glacier-fed catchments is difficult because errors in modelling snow accumulation can be offset by compensating errors in glacier melt. This problem is particularly severe in catchments with modest glacier cover, where goodness-of-fit statistics such as the Nash-Sutcliffe model efficiency may not be highly sensitive to the streamflow variance associated with glacier melt. While glacier mass balance measurements can be used to aid model calibration, they are absent for most catchments. We introduce the use of glacier volume change determined from repeated glacier mapping in a guided GLUE (generalized likelihood uncertainty estimation) procedure to calibrate a hydrologic model. This approach is applied to the Mica basin in the Canadian portion of the Columbia River Basin using the HBV-EC hydrologic model. Use of glacier volume change in the calibration procedure effectively reduced parameter uncertainty and helped to ensure that the model was accurately predicting glacier mass balance as well as streamflow. The seasonal and interannual variations in glacier melt contributions were assessed by running the calibrated model with historic glacier cover and also after converting all glacierized areas to alpine land cover in the model setup. Sensitivity of modelled streamflow to historic changes in glacier cover and to projected glacier changes for a climate warming scenario was assessed by comparing simulations using static glacier cover to simulations that accommodated dynamic changes in glacier area. Although glaciers in the Mica basin only cover 5% of the watershed, glacier ice melt contributes up to 25% and 35% of streamflow in August and September, respectively. The mean annual contribution of ice melt to total streamflow varied between 3 and 9% and averaged 6%. Glacier ice melt is particularly important during warm, dry summers following winters with low snow accumulation and early snowpack depletion. Although the sensitivity of streamflow to historic glacier area changes is small and within parameter uncertainties, our results suggest that glacier area changes have to be accounted for in future projections of late summer streamflow. Our approach provides an effective and widely applicable method to calibrate hydrologic models in glacier fed catchments, as well as to quantify the magnitude and timing of glacier melt contributions to streamflow.
Highlights
In many mountainous regions, glacier melt makes significant contributions to streamflow, in late summer during periods of warm, dry weather (Koboltschnig et al, 2008; Stahl and Moore, 2006; Verbunt et al, 2003; Zappa and Kan, 2007)
Jost et al.: Contribution of glacier runoff to streamflow in the upper Columbia River Basin glacierized areas”, which by definition includes the snow melt component, while Stahl et al (2008) reported only the glacier ice melt component as the relevant contribution of glaciers to streamflow because that is the component that diminishes as a direct result of glacier retreat
A second Latin Hypercube Search (LHS) with adjusted parameter ranges found 17 acceptable parameter sets, but histograms indicated that two parameters in the acceptable parameter sets were predominantly sampled near a range boundary and a third LHS with slightly refined parameter ranges was performed
Summary
Glacier melt makes significant contributions to streamflow, in late summer during periods of warm, dry weather (Koboltschnig et al, 2008; Stahl and Moore, 2006; Verbunt et al, 2003; Zappa and Kan, 2007). Understanding the quantity and timing of these contributions is important for a range of purposes, including short-term and seasonal forecasting of reservoir inflows and long-term projections of the potential hydrologic effects of climate change This knowledge is critical given that these contributions are likely to decrease in the medium to longer term as glaciers retreat (Gurtz et al, 2003; Koboltschnig et al, 2008; Marshall et al, 2011; Stahl et al, 2008), with implications for both water resources management and aquatic ecology (Moore et al, 2009; Zappa and Kan, 2007). Glacier mass balance observations are sparse and typically unavailable for most catchments
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