| Summary: | Climate warming can result in glacier contraction and changes in the coverage of snow, firn, and glacier ice that impact the energy balance and affect the timing and magnitude of streamflow generation. The impact of glacier-climate co-variability on streamflow in Canada’s northern continental regions remains undocumented. This study evaluates changes in glacier snow accumulation, ablation, and hydrological regime with changing climate for the Bologna Glacier in the Ragged Range (Selwyn Mountains) headwaters of the South Nahanni River, Northwest Territories. The Bologna Glacier basin was instrumented in 2014 with two meteorological stations that measured air temperature, relative humidity, precipitation, wind speed, and radiation on and off the glacier surface. These short term observations were used to spatially and temporally downscale and bias correct ECMWF Interim Re-Analysis (ERA-Interim) atmospheric reanalyses to construct a meteorological record from 1980 to 2015. Both the rainfall ratio and the average daily maximum summer temperatures were found to be increasing significantly over the study period. Total spring precipitation was found to be decreasing significantly over the time period. The Cold Regions Hydrological Modelling Platform (CRHM) was used to construct a physically based glacier hydrology model that incorporated a new glacier module: an energy balance snow and ice ablation model coupled with a blowing snow and avalanche model to characterize the mass balance of glacier snow and ice. To set up the model, the Bologna Glacier basin was discretized into Hydrological Response Units (HRUs) representing the spatial distribution of hydrological processes, parameters, and driving meteorology. HRUs were delineated by metrics including elevation, slope, aspect, firn limit, and land cover type, using a digital elevation model and Landsat satellite imagery from 1984 and 2014. Reconstructed meteorological data were used to force the model to run over three decades with the former (1984) and contemporary (2014, 2015) glacier geometry and firn limit configuration to determine the effect of climate warming, reduced glacier cover, and increased ice exposure on headwater streamflow generation, which was found to be substantial. Analysis of satellite imagery showed that the glacier area decreased by 14% from 1984 to 2014 (30 years) and that firn coverage was reduced from 82% to 47% over the same time period. Firn coverage entirely disappeared by 2015, as observed during the field trip in August of that year. There was a shift in CRHM-modelled discharge contribution from substantial firn melt contributions to substantial ice melt contributions between the historical and contemporary model configurations. Results indicate that both annual discharge and ice melt contributions to streamflow increased significantly over the study period. Overall, there was a substantial contribution to streamflow from glacier melt and wastage in all three model configurations. The envelope of annual mass balance was determined to be -9.0 m to -20.3 m water equivalent. The envelope of modelled summertime wastage contribution to measured streamflow at the Virginia Falls gauge in the South Nahanni River was determined to be 2.9 to 6.0%.
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