UBC Theses and Dissertations
Diagnosing the relative contributions of glacier retreat and climatic variability to streamflow trends in Illecillewaet catchment Chai, Zijie
Glaciers make significant contributions to streamflow in western North America. However, glaciers throughout the region are losing mass and retreating, leading to concerns about summer streamflow, particularly during extended spells of warm, dry weather. An empirical analysis of climatic and streamflow trends in the Canadian portion of the Columbia River basin found a regional climate-driven decline in August streamflow, which was augmented in glacier-fed catchments by glacier retreat. The objective of this study was to use a hydrological model to quantify the relative roles of glacier retreat and climatic trends on streamflow in Illecillewaet catchment. We applied a modified version of HBV-EC within the Raven modelling framework to Illecillewaet River, located in the Columbia River headwaters, from 1977 to 2020. The model was calibrated using daily streamflow, snow water equivalent from snow pillows and geodetic glacier mass change. The model was run for 1977-2020 with four scenarios: (a) declining glacier cover based on historical imagery; (b) constant glacier extent with 1985 glacier cover; (c) constant glacier extent with 2016 glacier cover and (d) no glacier cover. Key conclusions are: (1) in the Illecillewaet catchment, where glacier cover represents about 5% of the total area, glacier ice melt can contribute between 3.5% and 41.1% to the August streamflow; (2) the analysis of glacier ice melt trends showed a small but statistically insignificant increase, attributed to the synchronous rising of the snowline along with the retreat of the glacier terminus; and (3) the decline in August streamflow appears to have been primarily driven by climate influences, particularly decreasing precipitation in August. Currently, the presence of glaciers helps offset this declining trend, but the glacier compensation effect is weakening as the glaciers retreat.
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