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Climate Change and Canada’s Water Resources: Predicting the Future
The Mackenzie Basin covers 20 per cent of Canada, stretching from Jasper, Alberta, to the coast of the Beaufort Sea. For the past seven years, Environment Canada and university scientists have been toiling together in this vast landscape to learn more about the water and energy cycle in Canada’s North—information that is vital to predicting the impacts of climate change on our water resources.
Canada has some of the largest freshwater reserves in the world. These reserves fluctuate widely due to natural variations in climate, and concerns are growing that changes in climate caused by human activities could have dramatic and unpredictable effects. For example, as the largest single North American source of freshwater for the Arctic Ocean, the Mackenzie River—ranked tenth largest in the world by drainage area—plays an important part in regulating the thermohaline (temperature and salinity) circulation of the world’s oceans. A large-scale fluctuation in discharge from the Mackenzie would have consequences far beyond Canada’s borders.
The need to know more about the interrelationships between climate and water resources, especially in large, high-latitude river basins such as the Mackenzie, prompted Environment Canada and colleagues in the scientific community to launch a new research program in Canada’s North. Approximately 50 Canadian climatologists, meteorologists, hydrologists, remote-sensing experts and modellers from the Department’s Meteorological Service of Canada and National Water Research Institute, and several Canadian universities embarked on the Mackenzie GEWEX Study (MAGS).
MAGS is a major component of the World Climate Research Program’s Global Energy and Water Cycle Experiment (GEWEX), which is investigating water and climate interrelationships at important sites around the world—including the Mississippi and Amazon rivers, the Baltic Sea, and Asia’s monsoon and Siberian regions. Canadian scientists are playing a leading role in developing new knowledge about the processes that control the circulation, storage and distribution of water and energy in cold regions: processes that ultimately affect the global climate system.
Research on such a large scale poses many formidable challenges to scientists, particularly the difficulties of size, remoteness, and biophysical diversity in an area such as this. The Mackenzie Basin is made up of six main sub-basins, three great lakes—Great Slave Lake, Great Bear Lake and Lake Athabasca—and three major deltas, including the Peace Athabasca and Mackenzie. It encompasses Arctic tundra to the north, farm and ranchland to the south, lakes and wetland on the Interior Plains, mountainous regions in the west, and rocky Canadian Shield in the east. In most of the northern part of the basin the permafrost is continuous, and can be as thick as 500 metres.
The dramatic climate of the Mackenzie Basin presents its own challenges. Average monthly temperatures range from about 15ºC in summer to about –30ºC in winter. The range is much larger on a daily scale, however, with values from as high as 30ºC to as low as –50ºC. Large daily, seasonal and yearly variations in the basin’s cloud systems (and their structure) have a profound effect on surface processes, including the amount of heat gained and lost. Cyclonic storms are a frequent occurrence for a large part of the year and, in the summer, the Basin experiences a large amount of convective activity and associated lightning. These and other atmospheric processes were not well understood before MAGS was launched.
Researchers knew from the outset that they would have to contend with incomplete data, as there is a limited observational network in the Mackenzie Basin. They tackled this problem by making maximum use of the information they did have—for example, using historical precipitation and discharge records to estimate the distribution of precipitation and runoff over the Basin. They also developed research strategies using remote-sensing tools to gather data, which could then be applied in many ways, such as to calculate break-up and freeze-up dates for the Mackenzie great lakes and to estimate the surface-atmosphere exchange of heat and moisture in key regions.
Over the course of the study, Environment Canada established several new automatic meteorological observing stations at sites where data were sparse. Each site also represented a different biophysical region: near Fort Simpson, wetland with discontinuous permafrost; Fort Liard, mountains; the Great Divide between the Yukon and Northwest Territories, alpine tundra; Yellowknife between the Great Slave and Great Bear lakes, shield lakes; Fort Good Hope, northern forested wetlands; and Inuvik, boreal forest-tundra transition and continuous permafrost.
To gather critical hydrological data,
departmental researchers enhanced
their instrumentation in four long-term
research basins located in key
areas. Data collected at these sites
were augmented by data from a
Canadian weather forecast model.
Modelling experts made progress in
modifying the Canadian Regional
Climate Model for use over the
Mackenzie Basin, and in linking the
Canadian Land Surface Scheme with
a hydrological model. Integrating
these models is an important goal of
the study, and is essential for testing
our predictive ability under current
conditions and for considering how
climate and water resources will
change in the future.
Satellite image of the Mackenzie River Basin showing Great
Bear Lake (top) and Great Slave Lake (bottom).
With the help of these tools and
techniques, researchers focussed their
studies on large-scale atmospheric
processes, moisture recycling and
energy fluxes, and discovered much
new information about how moisture
is distributed and redistributed in the
area. During fall and spring, most
moisture and precipitation is
transported to the Basin along a
“conveyor belt” that moves from the
Pacific Ocean across the mountains.
The mountains play a major role in
converting this moisture into snow,
which then provides snowmelt and
runoff. In summer, evaporation from
vegetation and open bodies of water
is a major source of atmospheric
moisture and, along with convective
clouds, is an important factor in its
redistribution. Studies of the cyclonic
weather systems showed they are
responsible for a significant amount of
precipitation in the Mackenzie Basin.
From research on snow, ice and
permafrost, scientists gained greater
insights into how blowing snow is
redistributed, how effective forests are
at intercepting snowfall, and how
much snow is sublimated back to the
atmosphere. They determined that
water from melting snow infiltrates
easily into frozen organic soils but not
into ice-rich mineral soils, and that
slopes with permafrost are efficient at
moving water into streams, but those
without sometimes yield no runoff at
all. MAGS scientists are modifying
hydrological models to account for
these important variations.
Researchers investigating Great Slave
Lake found a pronounced difference
in cumulative annual evaporation
between two years. The first, lower
amount was consistent with estimates
for high-altitude lakes, but the
second, higher one was similar to
amounts estimated for the Laurentian
Great Lakes to the south. The higher
amount could be explained by an
exceptionally long ice-free period
that resulted from thinner ice-cover
in the second year, which, in turn,
resulted from above-average air
temperatures during an El Niño
warming episode. The researchers
believe that if an El Niño warming
has this effect, warming caused by
climate change from human
activities will also cause great lakes
in the North to behave more like
their southern counterparts.
As the first phase of the study draws
to a close, the MAGS team has
made unparalleled progress toward
understanding the links between
water and climate in high latitudes.
Five million dollars in new funding
from the Natural Sciences and
Engineering Research Council of
Canada has already been secured
for a second phase that will
continue to bring the government
and university science communities
together over the next five years to
produce better models and other
tools for improved prediction of
future changes to Canada’s freshwater
resources.
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