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.