Conclusions

Annual perturbations of observed hourly air temperature and precipitation were used to drive physically based cold regions hydrological models of the sensitivity of snow and runoff regimes in well-instrumented mountain research basins that span the northern North American Cordillera. Peak snowpack is sensitive to both warming and precipitation change in Wolf Creek in the subarctic Yukon and more sensitive to temperature in Reynolds Mountain in temperate Idaho. Peak snowpack is most sensitive to warming in the sheltered site in Reynolds Mountain and to both warming and precipitation change in the blowing snow sink regime in Reynolds Mountain, at lower elevations in Marmot Creek, and shrub tundra zone in Wolf Creek. Peak snowpack timing is more sensitive to temperature in Marmot Creek and Reynolds Mountain, but in Wolf Creek, precipitation more strongly affects the timing of peak SWE as temperatures remain largely below zero. Snow season start, end, and duration were found to be sensitive to warming in temperate Idaho and subarctic Yukon and to both warming and precipitation change in the continental Canadian Rockies (Marmot Creek).
The scenario with a severe climate warming and decreased precipitation in all three basins caused dramatic declines in SWE, a shortened snow-covered period, and decreases in annual runoff. The decreases in depth and advance in the timing of peak snowpack are weakly reflected in changes to runoff regime in each basin. The large changes in snowpack found here do not result in similar magnitude changes in annual runoff.
If precipitation decreases with warming, the impacts on snowpacks are amplified, with major implications for ecology, winter transportation, and hydrology. Smaller snowpacks and warmer weather would cause an increase in the snow-free period, which also would lengthen the evapotranspiration season, increasing the annual evapotranspiration loss. The importance of rainfall–runoff mechanisms in these basins increases while snowmelt decreases. Under warmer and drier climatic conditions, annual runoff decreases.
Increased precipitation, expected from some climate projections, can partially offset the effect of warming on snowpack and annual runoff. The role of precipitation as a compensator for the impact of warming on mountain snow hydrology is most effective in the colder high elevations and high latitudes and its effectiveness is reduced where snow regimes currently depend on blowing snow deposition, which is very sensitive to temperature. With increased precipitation, high elevation and high latitude basin snow and hydrological regimes can be resilient to warming. However, at lower elevations, and at lower latitudes the impact of warming cannot be offset by the projected maximum precipitation increases in future climates. The coupling of snow regimes to streamflow hydrology will remain strong in northern Canada but weaker in the mountains of Idaho and Alberta as the climate warms.