Page 302 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

266 part II The Water, Weather, and Climate Systems
CRiTiCALthinking 9.2 Calculate Your Water Footprint
How much water have you used today? From showers to tooth brushing to cooking and dish cleanup to quenching our thirst, our households have a water “footprint” that re- lates to affluence and technology. Just as you calculated your carbon footprint in Chapter 1, CT 1.1, you can calcu- late your water footprint at www.waterfootprint.org/index .php?page=cal/WaterFootprintCalculator. How does your individual water use compare to the average american’s? Can you think of ways to reduce your water footprint? •
water-development projects toward decentralized, com- munity-based strategies for more efficient technologies and increased water conservation.
Water Supply in Canada
The Canadian water supply derives from surface and groundwater sources. The supply of freshwater and some of the threats to it are outlined on the National Water Research Institute’s website (www.ec.gc.ca/inre-nwri/default. asp?lang=En&n=0CD66675-1&offset=10&toc=show). Canada has about 9% of Earth’s renewable water dis- tributed over 7% of Earth’s landmass. Water is accessed through rivers, lakes, ponds and reservoirs, groundwater aquifers, the snowpack, glaciers, ice fields, and the liquid and solid precipitation that replenishes all other sources. Measurements of precipitation recorded across the coun- try are difficult to aggregate because the hydrology of the landmass varies so greatly.
Figure 9.18 is a map of the streamflow in Canada found on the National Atlas website (atlas.gc.ca/site/english/ maps/archives/5thedition/environment/water/mcr4178). Insets por- tray the distribution of low flows, peak flows, and runoff. Peak flows occur earlier in the year to the south and are later to the north. Often, this results in spring flooding caused by ice jams, as the northern mouths of rivers are still frozen when the southern headwaters have melted. The map depicts volumes of flow in major streams and the width of the red colouration represents the volume of flow in cubic metres per second (m·s−1). This surface runoff (runoff plus streamflow), which varies between 75000 m·s−1 in low flow times to over 134500 m·s−1 in high flow times, is available for use.
The seeming abundance of water is mislead- ing when you consider that about 60% of Canada’s
freshwater drains to the north, while about 85% of the population lives within 300 km of our southern border. In other words, much of our water is not available in the heavily populated areas where it is most needed.
The difference between supply and demand is grow- ing with increasing urbanisation. All sources of freshwater are now under pressure from the growing, and often con- flicting, demands for domestic water supplies for munici- palities, for agriculture and industry, and for maintaining adequate streamflow in rivers that support aquatic ecosys- tems. There is also the added stress from the uncertain, but predicted, effects of climate change. Despite these growing stresses, many Canadians assume that governments will protect and sustain the freshwater supply.
Water Withdrawal and Consumption
Rivers and streams represent only a tiny percentage (0.003%) of Earth’s overall surface water (review Figure 9.3). In terms of volume, they represent 1250 km3, the smallest of any of the freshwater categories. Yet streamflow represents about four-fifths of all the water making up the surplus 1700 km3 · yr−1 that is available for withdrawal, consumption, and various instream uses.
• Water withdrawal, sometimes called nonconsumptive use or offstream use, refers to the removal or diversion of water from surface or groundwater supplies followed by the subsequent return of that water to the same supply. Examples include water use by industry, agriculture, and municipalities and in steam-electric power generation. A portion of the water withdrawn may be consumed.
• Consumptive use refers to the permanent removal of water from the immediate water environment. This water is not returned and so is not available for a sec- ond or third use. Examples include water lost to evapo- transpiration, consumed by humans or livestock, or used in manufacturing.
• Instream use refers to uses of streamflow while it re- mains in the channel, without being removed. Exam- ples include transportation, waste dilution and removal, hydroelectric power production, fishing, recreation, and ecosystem maintenance, such as sustaining wildlife.
Contaminated or not, returned water becomes a part of all water systems downstream. Canada uses only 9% of its withdrawn water for agriculture and 80% for industry. Figure 9.19 compares regions by their use of withdrawn water during 1998, graphically illus- trating the differences between more-developed and less-developed parts of the world.
Georeport 9.4 The Water It Takes for Food and Necessities
Simply providing the foods we enjoy requires voluminous water. For example, 77 g of broccoli requires 42 l of water to grow and process; producing 250 ml of milk requires 182 l of water; producing 28 g of cheese requires 212 l; produc-
ing 1 egg requires 238 l; and producing a 113 g beef patty requires 2314 l. and then there are our toilets, the majority of which still flush approximately 16 l of water. imagine the spatial complexity of servicing the desert city of las Vegas, with 150000 hotel rooms times the number of toilet flushes per day; of providing all support services for 38 million visitors per year, plus 38 golf courses. One hotel confirms that it washes 14000 pillowcases a day.