Page 277 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

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geosystems
Water Resources and Climate Change in the Prairies
In 1863, Captain John Palliser described a semiarid region extending from the foothills of the rocky Mountains to southwestern Manitoba (Figure gn 9.1), a region of grasslands and sandy soil in- dicative of a dry climate. The area, known as Palliser’s Triangle, was promoted to prospective settlers as mostly tree- less, requiring little clearing of forests for agricultural activities. The dryness should have served as a warning that the climate provided limited water resources and that drought could be a frequent occurrence.
in spite of the semiarid climate con- ditions, settlement took place in the 19th and 20th centuries in the southern prairies. Today alberta, Saskatchewan, and Manitoba have a combined popu- lation of 6 million people, with numbers increasing. The majority of people in these provinces live in or near Palliser’s Triangle.
There are concerns of an impending water crisis in this region. Future water supplies will not be adequate to meet the growing demand at current per cap- ita usage. Changes in water policies are required to accommodate population growth, fluctuations in climatic cycles, and the impacts of global climate change.
Many people are fooled by the “myth of abundance”; a belief in the idea that with so much freshwater, Canada could not possibly have concerns about water supplies. While Canada does indeed have large volumes of freshwater, much of it exists in areas of low population density, such as the north. in the south- ern prairies, where precipitation is low and evapotranspiration is high, particu- larly in the summer, water availability is dependent on rivers transferring supplies from areas with water surpluses to areas with water deficits.
“natural water tower” is a descrip- tion that applies to mountainous and highland regions on earth, from which excess water is available to supply rivers. The rocky Mountains are an example of a natural water tower feeding the north Saskatchewan and South Saskatchewan
0 250
500 KILOMETRES
▲Figure GN 9.1 The Palliser Triangle and the Saskatchewan, North Saskatchewan, and South Saskatchewan River basins. Mean annual precipitation is 419 mm at Calgary, 388 mm at regina, and 521 mm
at Winnipeg. in the southern prairies, the annual water budget deficit averages
35% to 50% of water need—water resource concepts discussed in Chapter 9. rivers originating in the rocky Mountains, fed by snow and ice melt, are critical to supplying water to this region.
climate for this settlement period was a departure from a drier past.
Climate change is bringing back a drier trend and adding stress to water resources.1 an important component to the water-tower supply is glacial-ice melt, yet glaciers in the rocky Mountains are diminishing as temperatures rise. increased melt rates have raised spring and summer discharge in mountain streams, but as glacier masses decrease, the contribution of melt water to river flows will decline. Furthermore, climate change is expected to cause tempera- tures to increase and precipitation to
1. a key scientific report is: Henderson, n. and Sauchyn, D., 2008, Climate Change Impacts on Canada’s Prairie Provinces:
A Summary of Our State of Knowledge, Prairie adaptation research Collaborative report no. 08-01, available at www .parc.ca/pdf/research_publications/ summary_docs/SD2008-01.pdf.
Saskatchewan River Basin
North Saskatchewan River Basin South Saskatchewan River Basin Boundary of Palliser’s Triangle
rivers that flow eastward through the southern prairies (Figure gn 9.1). Present intensive water extraction from these riv- ers and their tributaries is mainly for do- mestic water supplies and for large-scale irrigation.
The South Saskatchewan river, is “Canada’s most threatened river” as cited by the World Wildlife Fund Canada. The factors that led to this designation include: disruption of natural habitats and flow patterns by hundreds of dams in the basin; the annual extraction of 70% of water flow for agricultural and urban use; and predicted effects of ongoing climate change. a report on water supply and demand in the South Saskatchewan river basin is in the October 2010 issue of Canadian Geographic (see www .canadiangeographic.ca/magazine/oct10/ south_saskatchewan_river.asp).
Studies of climate in the southern prai- ries over the past two centuries—the time of nonnative settlement—confirm a view that the climate was actually more moist than in previous centuries. Climatic records, interpreted from evidence such as tree rings and sediments in closed lake basins, suggest that droughts were more com- mon and more severe in the past, and that
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N.W.T.
Nunavut
Manitoba
Hudson Bay
British Columbia
U.S.A.
Alberta
Edmonton
Calgary
Saskatchewan
Saskatoon
Regina
Ontario Winnipeg
Rocky Mountains