Freshwater Quantity and Quality in Canada:
Ecosystem interaction with a Changing Atmosphere
John W. Pomeroy Hydrological and Aquatic Sciences Division
National Hydrology Research Institute Environment Canada
Saskatoon, Saskatchewan
INTRODUCTION
The topic of this presentation is the impact of climate change on freshwater resources
in Canada, focussing on the interaction of ecosystems with a changing atmosphere
through the medium of surface water. The purpose of the discussion is to:
1) outline the role of freshwater in ecosystem response to and interaction with
atmospheric change, and
2) suggest the data required by Canada to anticipate and react sensibly to the impacts
of climate change.
The discussion will use examples that highlight Environment Canada scientific
advances in the present understanding of ecosystem-water-atmosphere interactions.
The data requirements will be those appropriate for a federal agency mandated with
identifying and ameliorating a national threat of this broad nature.
Freshwater has three irr~portant roles in ecosystem response and interaction with
atmospheric change. Freshwater is a
1) transmitter of atmospheric change to Canada's environment,
2) mediator of this change., and
3) host for aquatic ecosystems that are affected by this change.
As a transmitter, water is a flow of mass, energy and biochemical constituents through
and between ecosystems and between the surface and the atmosphere, as water,
water vapour, snow and ice; hence it transmits climate change impacts across the
country and across ecological and jurisdictional boundaries. It transmits the effect of
drought to soils as soil water and the effects of heavy precipitation downstream as
floods. Freshwater can mediate climate change to some degree because it is stored on
the landscape as lakes, snowcovers, glaciers, wetlands, rivers, and is a store of latent
energy. The latent energy of freshwater is extremely large; the energy used to melt a
gram of ice would raise the temperature of a grani of water 80°C and the energy used
to evaporate a gram of water would raise its temperature approximately 600°C if
evaporation did not occur. Water stored as snow reflects 80% of incoming solar energy
and therefore has a strong cooling effect. Despite the obvious importance of such a
surface energy mediator, the role of surface water in controlling climate change has not
had sufficient attention. As a host for organisms water is unsurpassed in Canada and
the subject of intense study. As water quantity and quality are affected by the changing
climate there is a direct impact on aquatic organisms with potential feedbacks to the
atmosphere through their transpiration and trace gas uptake or release.
FRESHWATER-ATMOSPHERE EXCHANGE
Freshwater atmospheric exchange can be viewed from various perspectives that are
driven by traditional scientific disciplines. From the point-of-view of physics, water is a
substance with a unique behaviour that covers the land as a liquid, solid and gas; it
travels easily, has a highly variable reaction with radiant energy and can store large
quantities of latent energy. Distinctive to water are its incompressability as a liquid and
that the solid form is less dense than the liquid. Life on our planet would be
unrecognizable without these water properties. From a chemical perspective, water is
an extremely strong solvent and transport medium for various acids, geochemicals and
organic molecules. It transports nutrients, pollutants and geochemicals to, from and
around the Earth's surface, and is critical to the geochemical cycling of the planet.
Biologists have long documented the strict requirements that life forms have for water,
either as habitat or for consumption. The organisms have adapted to certain quantity
and quality conditions but also exert a controlling feedback on water quality. With
respect to society - and Canadian society is outstandingly dependent upon large
aniounts of water - Canada is known to have a disproportionately-large amount of the
Earth's fresh water resource. This resource is not efficiently used however, as we have
adapted to the present generous supplies. Our neighbours are well aware of this
situation. Economic demand for water is confounding to its management as this
demand is highly inelastic. Plentiful, clean water has little or no value but when in short
supply it becomes almost priceless as it is necessary for life on a daily basis.
Therefore, if the balance between supply and demand of North American water
changes because of changes in precipitation, quality or evaporation, we will have to
respond to dramatic internal and external pressures. The outcome of such pressures
on our industry, agriculture and recreation may not be positive or pleasant.
Hydrology brings together the various perspectives of water-atmosphere-ecosystem
exchange by consideration of the hydrological cycle. Figure 1 shows the hydrological
cycle over Canada, in which we have atmospheric water vapour transport (clouds,
vapour) evaporation feeding the atmospheric vapour from oceans and various
mountain, forest, agricultural and arctic ecosystems, and then water returning to the
surface as either rain or snow. Much precipitation infiltrates the soil where it can be
used by plants for evapotranspiration or can drain deeply to replenish groundwater.
Precipitation in excess of infiltration, evapotranspiration and drainage requirements is of
very great interest because it moves along the land surface as runoff or streamflow.
Because of runoff, continental water returns to the oceans and can cross normally dry
land surfaces. Hence even if there is a local drought, a river flowing through to a lake
or a wetland can produce evapotranspiration and provide a habitat. When irrigated this
water can replenish soil water supplies. An irr~portant store of water is in groundwater
aquifers, so that even if we temporarily run out of surface supplies, we can withdraw
from this "bank account" for awhile.
WATER IN GLOBAL CLIMATE SIMULATIONS
It is important to consider how global circulation models (GCMs) handle surface water
in .their predictions of climate change and their (in)ability to predict the impacts of this
change. Of first note is that the present simulations are unable to obtain a correct
surface water balance. These models inacc~~rately represent surface hydrology, by
causirig simulated rivers to appear to flow uphill, or causing simulated plants to
completely shut down during droughts because the models are atmospherically derived
and do not sufficiently consider hydrological systems yet. We hope that they will soon,
with assistance from hydrologists.
Another point that GCMs need to consider is that many natural ecosystems manage
their climate by managing their water because it is the most practical and efficacious
way to store energy on the surface. Canadians try to do this in agricultural ecosystems
by spacing plants, irrigating, snow management, crop combinations, etc. Because of
the important control and response of regional ecosystems to water fluxes and storage,
links between ecosystem and atmospheric dynamics must focus on fresh water as the
mediator and transmitter of that link.
An example of how GCMs handle the water balance is given for the Mackenzie River
Basin of northwestern Canada. Hydrologists are interested in this basin for a number of
reasons. It has a lot of very Canadian distinctions to it - glaciers, wetlands, permafrost,
snow melt, etc. It is also of interest because it flows into the Arctic Ocean. The
Mackenzie River provides the largest input of fresh water to the Arctic Ocean from the
North American continent, and is very important for ocean and icepack dynamics. It is
one the world's largest river basins, in an area expected to experience a lot of climatic
change; hence, it is the Canadian focus of the Global Energy And Water Cycling
Experiment of the World Climate Research Programme. As shown in Fig. 2, the
Mackenzie basin is covered by 30 grid points of the Canadian Climate Centre (CCC)
GCM. The resolution of any climate simulation of the basin is therefore very coarse.
Each of the grid cells is one GCM grid point for which there is a climate and water
sinlulation. Each cell has a water balance with the excess simply "flushed" directly
through the basin without hydrologic controls. Figure 3 shows a ten-year "present
climate" average of the CCC GCM outputs of water flow routed through the Mackenzie
River, the results of the GCM climate parameters fed into a process-based hydrological
model developed at by Dr. Geoff Kite of NHRl called "SLURP", and measured average
discharge of the Mackenzie. It is evident that the GCM has serious deficiencies in
predicting hydrology. It is predicting the peak runoff event several months early and
almost an order of magnitude larger than it actually is, and late summer flows are badly
underestimated. These errors can be largely corrected by inclusion of a hydrological
component such as that developed by Dr. Kite.
A hydrological model with the GCM data can be used to simulate a large basin
relatively easily because storage and routing of water dorr~inate the basin response. It
is not as simple to simulate the runoff of a smaller basin with a hydrological model
because other hydrological processes become important at small scales. These scales
are much smaller than the present GCM grid cell which calls into question the intrinsic
ability of GCMs to help predict surface hydrology irnpacts. lniprovements to this
situation are being led by land-surface schemes that are being attached to GCMs.
Canada is fortunate to have developed a model called "CLASS" - the Canadian Land
Surface Scheme, to represent the interaction of GCMs and the Earth's surface. In a
recent intercomparison, CLASS was found to be the most hydrologically accurate of
any land surface process model; however, when we examine it in detail, we find that
the hydrological processes are not always realistically represented in this model and
hence it can produce some unrealistic results.
An important aspect of climate change impacts in Canada is the depletion of a snow
covered area during snowmelt. This is very important for the albedo feedback to the
energetics calculation of GCMs, for calc~~lating snowmelt runoff in the spring, and also
for various ecological factors: birds need snowfree land to nest, the rate of melt
determines runoff versus infiltration and hence the filling of wetlands. Comparing
CLASS with a snow hydrology model developed by Dr. Kevin Shook of Saskatoon in
Fig. 4 shows that CLASS predicts complete snow cover disappearance on the Prairies
when the snow covered area is actually about 90%, and about three weeks before the
actual disappearance. This error has a substantial impact through the whole
hydrological and ecological system. The simulation was run for Bad Lake, where we
have good measured data dating from the International Hydrological Decade in 1972.
One of the research programmes at NHRl right now is an attempt to improve models
such as CLASS so that they would adequately represent this type of phenomena.
A phenomenon often neglected by hydrological models and atmospheric models is
snow accumulation. There are a lot of very important processes here that are
extremely important to Canada because most of the country is snow covered for about
half of the year and northern areas for even longer. Hence the stored seasonal snow
cover leads to the largest annual runoff events in most of Canada. Snow cover
provides about 80% of runoff in the Prairies, in the Boreal forest about 50%, and up in
the Arctic it creeps up again to 60, up to 80-90% in the high Arctic, and somewhat less
in some of the more temperate regions. This is critical because snowmelt recharges
the lakes, various wetlands, bogs and fens around the country. The amount and timing
of snowmelt runoff are very strongly influenced by ,the amount of snow on the ground.
The amount of snow on the ground in spring is not that which falls, but rather that which
falls and is not redistributed by either the forest cover or by blowing snow, and that
which is not melted over the winter. What we have found is that it is very rare in fact
that you find a situation where the amount of snow that falls equals that which is on the
ground, and no atmospheric models have incorporated this effect yet. Figure 5
presents all exarr~ple from an Arctic basin where there are dramatic losses in the
amount of snow, or gains in certain areas, that are governed by blowing snow
processes and their interaction with the vegetation cover. This sort of variation needs
to be incorporated into hydrology models and GCM and NHRl has a programme to do
just that.
In Fig. 5, data are presented from the GEWEX experimental watershed in the Western
Arctic north of Inuvik. Here the ecosystem exerts a tremendous hydrological control on
the precipitation, amount of snow melt and runoff. If there is a climate change
response that would result in a change in the spatial distribution of this vegetation, we
would see a dramatic change of runoff, even if there is no change in the snowfall.
CLIMATE WARMING - THREATENED REGIONS.
Is all of Canada equally threatened? The U.K. Meteorological Office Unified (Hadley
Centre) GCM includes a coupling to oceans and the cooling effect of sulphate aerosol
and shows that areas that are strong sources of sulphate are not going to experience
the strongest warming. This is matching historical trends very well. The result is that
only moderate warming is anticipated for southeastern Canada, in the Great Lakes, St.
Lawrence area: + I to +2OC. Western and northern Canada apparer~tly will experience
the strongest warming in the Northern Hemisphere (+2 to +5 C), and we might want to
target these very strongly threatened ecosystems. Figure 6 is a map of predictions of
mean temperature change In 45 years by the Hadley Centre GCM. It is the most recent
run of the model for Canada, and you can see ,that eastern Canada is looking at just lo
C warming under that prediction, whereas western and northern Canada will still
experience a fairly strong warming. The impact of climate change on the water
resources of western and northern Canada should therefore be targeted by the
Department.
CLIMATE VARIABILITY - ECOSYSTEM RESPONSE
All of Canada may be expecting increased variability of weather and frequency of
destructive weather, often manifested by destructive hydrological phenomena. The
ecosystem manifestations of this weather will be moderated or exacerbated by
freshwater impacts. The frequency of frost is affected by soil moisture and atmospheric
moisture; frequency of blizzards is strongly affected by air temperature and snowfall;
the flooding recharge of delta lakes is affected by upstream snow cover and the rate of
snowmelt; forest fire incidence will depend upon soil moisture. In Saskatchewan 10%
of the commercial forest burned in the spring of 1995 due to abnormally hot dry
weather. In spring of 1996, there occurred substantial snowmelt floods in the same
province. Depletion of oxygen in lakes is linked to inflow timing and quality. An
increasing frequency of droughts can reduce summer streamflow and increase the
solute concentration in certain surface water supplies. That may lead to salinization in
irrigation areas, increased dissolved solid load in some situations and toxicity in others.
These manifestations are typical of increased variability but it cannot easily be
statistically verified yet.
FRESHWATER QUANTITY RESPONSE, CONTROL AND FEEDBACK
When we consider climate change and freshwater quantity, it can be examined with
respect to the response of the freshwater system, the control exerted by the freshwater
system, and the feedback to the climate system from freshwater. In Canada in general
there could be a shorter snowcovered season, and an earlier melt. In areas where the
snowcover forms and melts periodically over the winter, there will be greater winter
flooding; as in eastern Canada and the western mountain regions. Greater frequency
of summer droughts is expected, particularly in the Prairies and Southern Ontario, and
in response to the quantity change, a biomigration of species from areas limited by
water. One would be a northward movement of the rrrixed wood forest into the present
Boreal forest, northward movement to the Prairies into the mixed wood forest belt,
rangeland perhaps into Prairie zones, and the retreat of trees from B.C. interior valleys.
We are also going to have movement of the temperate forests in the east into some of
the Boreal forest areas. As a result, there will be a reduction of wetlands and lakes in
general across Canada. In the Prairies there will be a drying of many Prairies sloughs
dependent upon the snowmelt runoff; a reduction in Boreal lakes which are also
dependent upon this local runoff, and the drying of river delta lakes that depend on the
spring flood. Dr. Terry Prowse of NHRl finds that there is some indication that the
drying of the Peace-Athabasca Delta lakes is due to a decline in Alberta snow cover.
The floodplain lakes in the Mackenzie delta are an extremely important aquatic habitat
for muskrat and waterfowl and important for many other species. A simulation done by
Dr. Phil Marsh at NHRl on the Mackenzie delta lakes showed that with a 2xCO,climate,
in about ten years the lakes begin a substantial retreat in size because of reduced
flooding. This is one example of increased and protracted variability in water supply
across the country. Another example is Fig. 7 showing discharge of the Kootenay River
in British Columbia. Dr. Kite's SLURP Model is run using the outputs of the Canadian
Climate Centre GCM for the present climate (IxCO,) over a series of years, and you
see in the top graph, the simulated and recorded flows are matched quite well over this
period of record. In the bottom graph the IxCO, simulation indicates a single spring
flooding event, usually in MayIJune. For comparison is a 2xC0, simulation which
indicates floods at any time in the winter. In certain cases the warmer climate produces
serious winter floods and higher flow in tlie fall. Essentially what is going on here is that
precipitation, instead of falling as snow, is falling as rain, and flushing through the
system much more rapidly.
For streams draining small basins on the Prairies, spring is the time of runoff and often
the only time when runoff is produced. One of the predictions with a warmed climate in
winter and spring, is ,that we may not have fully frozen soils as they are now. Because
there are normally summer shortages of water on the Prairies, this limits the annual
runoff considerably. Dr. Raoul Granger of NHRl has produced a frozen soil infiltration
routine and incorporated this routine in a standard hydrological model. If we take that
frozen soil routine out and replace it with an unfrozen soil calculation, a good simulation
of hydrological response of prairie basins to a warmer climate is developed. The
change is shown in Fig. 8 with the two matching hydrographs showing measured and
presently predicted runoff and the very low hydrograph showing what is predicted under
a warmer climate. The warmer climate prediction suggests that runoff will drop to
almost nothing, so if you are a duck, it is going to be a hard time. This is also very bad
if one is a farmer dependant upon surface water supplies. The runoff from mountains
and the Prairies, though small, has a very important effect on small towns, on the
agricultural area, and upon the wildlife.
There are some interesting links through evaporation between ecosystem productivity
and climate. Dr. Raoul Granger has measured the temperature and vegetation density
of a boreal forest landscape using satellite remote sensing, the results are shown in
Fig. 9. It is evident that there is an inverse relationship between mid-summer
temperature and vegetation density. NHRl research in the Model Forest Programme
has shown that this is due to evapotranspiratioli .from the more heavily vegetated
surfaces. Evapotranspiration cools the surface, resulting in the temperature
differences. Hence, by clearcutting the boreal forest we are causing local climate
changes that are quite severe. To illustrate the severity of the climate change, Fig. 10
shows the surface temperature measured over one particular day in June, right around
this time when 10% of the commercial forest in Saskatchewan was burning. The
surface temperature goes up to about 30" C everywhere except the clearcut where it
goes up to 45" C, 15" higher than is "natural". 'This is a sort of local climate change
that can be created at the surface if we are not too careful. The disturbing thing for
forestry is that the wilting point for spruce seedlings is about 36" C and hence by
clearcutting they have created an envirol-~ment unfavourable for growing trees.
FRESHWATER QUALITY RESPONSE TO ATMOSPHERIC CHANGE
It is anticipated that as well as climatic change, there is a potential chemical change
that would results in increased availability of nitrogen to terrestrial and aquatic
ecosystems. In Canada, this could be due, in part, to warmer snow packs that will
sustain a greater deposition velocity of nitric acid vapour and hence a greater
fertilization of snow by nitrogen species, and as well as the simple increase of
anthropogenic nitrogen in the air, which has not been reduced like sulphate. As a
result, there may be productivity increases in certain ecosystems, perhaps
eutrophication in a few situations.
As snow melts earlier under a warmer climate, infiltration will increase because of the
development of unfrozen soils, reducing runoff to streams and transferring much of the
acid snow impact to land. Many ecosystem impact models suggest increased soil and
plant productivity because of increased retention of nitrogen on land, but also the
decline of certain forest species because of nitrogen saturation in certain ecosystems.
Nitrogen saturation is not an issue in Canada, but it might become one in the future.
Impacts to lakes and streams will din-~inish simply because many acids will not reach
the lakes and streams with a reduced spring snowmelt. Modelling results suggest a
reduction in the loadirlg of acids to lakes and the reduced episodic releases of
contaminants. For eastern Canada a 10-50% reduction in episodic acid shock is
predicted because of a less flashy spring snow melt. This prediction considers only
climate change without any change in atmospheric sulphur.
Other points to consider are an increased solution of basin geochemicals with a
decreased stream transport capability, leading to an increase in the solute load and
salinity of certain aquatic systems . Warming of and a higher evaporation from lakes
will increase eutrophication and solute levels in the Prairies, southern Ontario and
possibly the Arctic, while snow melt reduction to the Boreal forest lakes will reduce the
solute load and cause possible UV-B penetration increases. There will be a change in
wetland distribution as oligotrophic bogs may degrade into fens in certain regions.
WATER-ECOSYS'TEM FEEDBACKS TO ATMOSPHERIC CHANGE
Positive feedbacks to the system are decreased snow cover resulting in decreased
albedo, increased net radiation at the surface and hence surface warming; and
decreased forest/ wetland1 lake cover causing decreased evaporation and hence,
enhanced surface warming. That's bad. What's good? Increased productivity will
increase carbon fixation in the boreal forest and the Arctic in particular. This would
lower greenhouse gas levels beyond what they might be. Increased evaporation rrlight
increase cloud cover and increase precipitation which would result in a cooling of wetter
surfaces and higher productivity again. Figure 11 shows ,the relationst-lip between
primary productivity and actual evaporation or evapotranspiration. The higher the
productivity, the greater the evapotranspiration that can be generated. Figure 12
illustrates a positive feedback: the relationship between North American snow cover in
nill lions of square kilometers and temperature anomalies in winter. The wide line is the
North American maximum temperature in the snow regions showing a lo increase. That
results in about a million square kilometer reduction in North American snow cover: a
dramatic relationship we can already measl-ire, and we would expect that to continue.
RESEARCHANDDATANEEDS
What do we need from modelling right now? We require Canadian atmospheric models
with realistic sulphate aerosol, cloud, surface hydrology, snow and ice, ocean and
biophysical land cover interactions. That's quite a shopping list, but all are required if
we are to determine hydrological impacts in Canada. For water quantity, models must
be physically based and in agreement with field measurements. We need good field
measurements of temperature, precipitation, and radiation for the regions of Canada on
a seasonal basis. We must link continental scale hydrological models to atmospheric
models, and within these continental scale models, nest mesoscale and small scale
hydrological models so we can determine impacts at a local scale: then link these down
to hydrological process models that will tie into terrestrial and aquatic ecosystem
models.
For water quality, in addition to the these requirements, we need to know the
atmospheric deposition of contarrlinants and major geochemicals, and we need river,
lake and wetland hydroecology models, and terrestrial hydroecology models linked to
aquatic and a'tmospheric models.
Regarding data, for water quantity we need to focus on threatened areas: the West
and the North, the ecotones, the transitions between the present biomes, critical
habitats, sensitive environments, and small catchments that will show these changes
quickly. Where appropriate, remote sensing could be used as a cost-effective means to
gather vegetation, snow cover, soil moisture, and surface temperature data. For water
quality, with flow measurements we could also obtain nitrogen and phosphorous,
dissolved solids and salinity measurements: nitrogen export indicates the health of
the hydroecological system. For lakes, rivers and wetlands we require dissolved
oxygen, nutrients, water temperature and species composition (not only for commercial
species) data. We must monitor change in the distribution of aquatic and terrestrial
habitats and the biophysical characteristics of these habitats.
AMELIORATION OF FRESHWATER IMPACTS
How might we ameliorate the freshwater impacts? We can preserve forests in
threatened areas: for exarr~ple, the mixed wood of Western Canada. We need
integrated land use and stream flow regulation management in threatened basins. An
example here is the drying of the Peace Athabasca delta, which is regulated by a dam
and undergoing climatic change. The dam provides a chance to restore the natural
flow. We can also promote carbon-fixing land uses; water conservation measures in
areas that will experience shortages, perhaps urban areas; irrigation where supply and
salinization warrant according to our best predictions; snow management on the
Prairies, which might be one way to decrease the albedo and to augment supplies
without irrigation or major dams; and this niight be controversial but we may have to
introduce plant species or genetically engineer plant species that manage water more
effectively to promote negative feedback.
CONCLUSIONS
To conclude, the impacts of what are goiog to be unprecedented, at least in recent
time, atmospheric change impacts on water resources of Canada, their prediction and
mitigation, are going to present quite a challenge to our government agencies and we
must coordinate internally, internationally and interprovincially. The issues - local,
national and international - cannot be separated. The impacts are multi-scale, and
there are severe and occasionally catastrophic local implications for the ecological
health of Canada and the livelihood of Canadians. Strategies for prediction and
mitigation, therefore, must be national with regional emphasis on vulnerable areas. In
closing, I would like to extend thanks to all the people I was able to collaborate with to
gather this material.
MACKENZIE RIVER BASIN CCC - GCM GRID POINTS
I GCM water excess - Recorded SLURP wfth GCM data
0 1 I I I I I I I I I I I
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Snow Accumulation (mm)
A Anticipated Mean Temperature Change due to MADLEV CENTRE FOR CLIMATE PREDICTI[N W RESEARCH Greenhouse Gases and Sulphate Loading
with Ocean Coupling, 2040
-6 -4 -2 0 2 4 6
Temperature Change OC
Environment Environnement PSI Canada Canada
Discharge (m3. s-') Discharge (m3. s-')
Aspen
Pine
Pine lantation *
Clearcut
Fresh clearcut
Normalized Index V
Surface Temperature, "C
NEGATIVE FEEDBACK: Primary Productivity - Actual Evaporation
2 2.5 3 Actual Evaporation {Evapotranspiration)
( w l )
POSITIVE FEEDBACK: Snow Cover - Air Temperature
- North American Mean Maximum Temperature - snow regions
- Northern Hemisphere Mean
~emperatur6 Anomaly (C)