Diagnosis of future changes in hydrology for a Canadian Rockies headwater basin
Authors: Fang Xing , Pomeroy John W. 
Published: May 2020

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.