Abstract
Abstract. Climate change is anticipated to impact the hydrology of the Saskatchewan River, which originates in the Canadian Rockies mountain range. To better understand the climate change impacts in the mountain headwaters of this basin, a physically based hydrological model was developed for this basin using the Cold Regions Hydrological Modelling platform (CRHM) for Marmot Creek Research Basin (∼9.4 km2), located in the Front Ranges of the Canadian Rockies. Marmot Creek is composed of ecozones ranging from montane forests to alpine tundra and alpine exposed rock and includes both large and small clearcuts. The model included blowing and intercepted snow redistribution, sublimation, energy-balance snowmelt, slope and canopy effects on melt, Penman–Monteith evapotranspiration, infiltration to frozen and unfrozen soils, hillslope hydrology, streamflow routing, and groundwater components and was parameterised without calibration from streamflow. Near-surface outputs from the 4 km Weather Research and Forecasting (WRF) model were bias-corrected using the quantile delta mapping method with respect to meteorological data from five stations located from low-elevation montane forests to alpine ridgetops and running over October 2005–September 2013. The bias-corrected WRF outputs during a current period (2005–2013) and a future pseudo global warming period (PGW, 2091–2099) were used to drive model simulations to assess changes in Marmot Creek's hydrology. Under a “business-as-usual” forcing scenario, Representative Concentration Pathway 8.5 (RCP8.5) in PGW, the basin will warm up by 4.7 ∘C and receive 16 % more precipitation, which will lead to a 40 mm decline in seasonal peak snowpack, 84 mm decrease in snowmelt volume, 0.2 mm d−1 slower melt rate, and 49 d shorter snow-cover duration. The alpine snow season will be shortened by almost 1.5 months, but at some lower elevations there will be large decreases in peak snowpack (∼45 %) in addition to a shorter snow season. Declines in the peak snowpack will be much greater in clearcuts than under mature forest canopies. In alpine and treeline ecozones, blowing snow transport and sublimation will be suppressed by higher-threshold wind speeds for transport, in forest ecozones, sublimation losses from intercepted snow will decrease due to faster unloading and drip, and throughout the basin, evapotranspiration will increase due to a longer snow-free season and more rainfall. Runoff will begin earlier in all ecozones, but, as a result of variability in surface and subsurface hydrology, forested and alpine ecozones will generate the greatest runoff volumetric increases, ranging from 12 % to 25 %, whereas the treeline ecozone will have a small (2 %) decrease in runoff volume due to decreased melt volumes from smaller snowdrifts. The shift in timing in streamflow will be notable, with 236 % higher flows in spring months and 12 % lower flows in summer and 13 % higher flows in early fall. Overall, Marmot Creek's annual streamflow discharge will increase by 18 % with PGW, without a change in its streamflow generation efficiency, despite its basin shifting from primarily snowmelt runoff towards rainfall-dominated runoff generation.
Highlights
The eastern slopes of the Canadian Rockies form the headwaters of the Saskatchewan River basin (SRB) and are a vital source of water supply to downstream users in the Prairie Provinces of Canada
Near-surface hourly air temperature, relative humidity, wind speed, precipitation, and shortwave irradiance from observations, uncorrected Weather Research and Forecasting (WRF) CTRL outputs, and bias-corrected WRF CTRL outputs were compared for the Centennial Ridge, Fisera Ridge, Vista View, Upper Clearing, and Upper Forest stations in Marmot Creek Research Basin (MCRB), and the comparisons are shown in the quantile–quantile (Q–Q) plots (Fig. 3)
A physically based hydrological model was set up using the Cold Regions Hydrological Modelling platform (CRHM) platform and was forced by bias-corrected 4 km WRF near-surface meteorology outputs in CTRL (i.e. 1 October 2005 to 30 September 2013) and pseudo global warming” (PGW) (i.e. 1 October 2091 to 30 September 2099) periods to assess the future changes in hydrology at Marmot Creek Research Basin
Summary
The eastern slopes of the Canadian Rockies form the headwaters of the Saskatchewan River basin (SRB) and are a vital source of water supply to downstream users in the Prairie Provinces of Canada. These high mountain headwaters occupy only 12.6 % of the SRB’s total drainage area but provide 87 % of streamflow, which is used downstream for agri-. Pomeroy: Diagnosis of future changes in hydrology for a Canadian Rockies headwater basin culture, communities, and industries (Redmond, 1964) Climate in this region has been experiencing changes since the last century (Whitfield, 2014; DeBeer et al, 2016). With further climate change expected in the future (IPCC, 2013), understanding the impacts of projected climate change on the hydrological cycle in mountain headwater basins is important for evidence-based water management of the SRB in the future
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