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Importance of snow for water resources in Canada:
The hydrology of most Canadian river basins is dominated by seasonal storage of water in the snowpack. The melting of this water in the spring results in a pronounced pulse of fresh water that is vital for natural and human systems (e.g. river and lake ecosystems, fresh water fisheries, agriculture, hydro-electricity generation and drinking water). Semi-arid regions such as the prairies and interior valleys of British Columbia are especially dependent on snowmelt runoff which can supply in excess of 80% of total runoff. A discussion of the impacts of reductions in snow cover is provided in Fitzharis (1996).
Recent trends in snow cover in Canada:
Recent warming and changes in atmospheric circulation patterns over North America have resulted in reductions in the duration of the snow cover season, the amount of water stored in the snowpack, as well a widespread trend toward earlier spring melt. These changes are particularly pronounced over western Canada (see Figure 1 below) where spring melt has advanced at a rate of close to half-a-day per year over the period since 1955. Reduced storage of water in the snowpack and earlier melt translate to a lower fresh water pulse for recharge of soil moisture and reservoirs, and increased potential for evaporation loss. This trend, coupled with increasing demand for water, suggests increasing conflict in the use and management of snowmelt-derived water supplies. It is not possible at this stage to directly link recent changes in snow cover to global warming. However, the changes are consistent with climate model simulations forced with increasing levels of greenhouse gases. For more information on this topic please see "Is Snow Cover Changing in Canada".
Average change (days/yr) in snow cover duration in the second half (Feb.-Jul.) of the snow year over the period 1972-2000. Derived from the NOAA weekly satellite snow cover dataset.
Snow cover response to climate warming:
Snow cover is an integrated response to both temperature and precipitation and exhibts strong negative correlations with air temperature in most areas with a seasonal snow cover. Because of this temperature association, Global Climate Model (GCM) simulations suggest widespread reductions in snow cover over the next 50-100 years in response to increased levels of greenhouse gases in the atmosphere (see animation below).
Simulated change in February mean SWE by the Canadian GCM (CGCM2) over the 1985-2085 period in response to increasing concentrations of greenhouse gases (IPCC-IS92a forcing scenario). Data courtesy Canadian Centre for Climate Modelling and Analysis.
There is, however, considerable variability in model-projected regional patterns of snow cover change (Frei et al., 2003). One of the main reasons for this is that GCMs have difficulty simulating precipitation over high elevation and high latitude regions. Another complication is the role of atmospheric circulation patterns. Moore and McKendry (1996) showed that snowpack conditions in southern British Columbia were dominated by atmospheric circulation patterns linked to decadal-scale variatibility in Pacific Ocean sea surface temperatures. They also found evidence of an abrupt change to less winter snow accumulation after 1976 which coincided with a well-documented shift in the Pacific-North America (PNA) teleconnection pattern to more positive values (Leathers and Palecki, 1992). This shift has been associated with reduced snow cover, earlier runoff and more negative glacier mass balances over much of western North America. Brown (1998) showed that ENSO was responsible for significant anomalies in regional snow cover over western Canada with El Niño associated with below-average winter snow cover extent, and La Niña with above-average SWE. Abrupt shifts in atmospheric circulation such as the 1976 change in the PNA pattern and a recent tendency toward more frequent El Niño events add an additional level of uncertainty onto the regional snow cover response to large scale climate warming.
References:
- Brown, R.D., 1998: El Niño and North American snow cover. Proc. 55th Eastern Snow Conference, Jackson, NH, June 4-6 1998, 165-172.
- Fitzharris, B.B., 1996: The Cryosphere: Changes and their Impacts. Intergovernmental Panel on Climate Change, WGII Report, Cambridge University Press, pp. 241-265.
- Frei, A., J.A. Miller, and D.A. Robinson, 2003: Improved simulations of snow extent in the second phase of the Atmospheric Model Intercomparison Project (AMIP-2). J. Geophys. Res. - Atmospheres, 108(D12), 4369-4386.
- Leathers, D.J., and M.A. Palecki, 1992: The Pacific/North American teleconnection pattern and United States Climate. Part II: Temporal characteristics and index specification. J. Climate, 5, 707-716.
- Moore, R.D., and I.G. McKendry, 1996: Spring snowpack anomaly patterns and winter climatic variability, British Columbia, Canada. Water Resources Research, 32, 623-632.
This information was provided by Ross Brown, Meterological Service of Canada. | |
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