Friday, December 07, 2007

The big Thirst

As we hear of water shortages in Australia, the U.S. and many other places, it is clear that water resources are now more than ever, a global concern.
As reported by the World Water Council the last century has seen the human population triple and water consumption grow six-fold. In the eyes of the council, this growth in consumption has occurred in a context in which water is a renewable resource.
While a simple model of the hydrological cycle would support this hypothesis, the way in which we currently use water has transformed the notion of “temporarily borrowing water” from the cycle, to “mining water” out of the cycle.
Mining water refers to how in every instance that it is used, it is returned to the environment in a way that is unfit to sustain the functions of other systems or organisms later in the cycle (i.e. it is heated, it contains excess nutrients, heavy metals, sewage etc.).
The “mining” of water also means that in some instances, over-extraction leads to the inability of an aquifer to ever fully recharge because of saltwater intrusion or land subsidence-rendering it non renewable.
Several factors may account for this. Climate change, as many scientists will say, is involved with changing the precipitation patterns that would normally resupply the depleted aquifers and rivers. Over-consumption of water compounded by the pressure of population growth is another. The problem we face is multifaceted in that demand is increasing as supplies are declining where it is needed.

As the majority of the population is establishing itself in cities, what does this water crisis mean for populations living there? Is it even a problem in municipalities? To get an idea of the breakdown in water usage in Canada, the David Suzuki Foundation indicates that the major users of water in Canada are the power generation industry 64 %( i.e. water is used as a coolant– does not include hydroelectric generation), 14% for manufacturing, 12% in municipalities, and 9% for agriculture.
The USGS, informs us of the major U.S. water users: power generation uses 48% of water, while irrigation uses 34% and public/domestic uses represented 12%. At first glance, it would seem that municipalities are only responsible for ~12% of the water consumption in North America, and that conservation strategies should be focused elsewhere, like in power generation, irrigation or manufacturing.
Surely these measures must be implemented, but it does not absolve the city of responsibility, especially since common sense would tell us water usage in these “other” sectors are likely a function of the demands of cities.
That is to say, why is all this power produced? why is all this food grown? -in large part, to power and feed cities. Regardless of which sector seems like the biggest drain on water resources, large and small municipalities are suffering and facing some hard decisions related to how to best manage what is left.

Among the largest cities in the world, Mexico City and Shanghai are perfect examples of the drastic effect of overextraction of groundwater. In both cities, water is being drawn from their aquifers at twice the rate that they are being recharged. Partly because of this overpumping as well as the weight of skyscrapers, Mexico city has subsided by ~30ft in the past 100 years while Shanghai has dropped 2 meters in a similar time frame. While this sinking represents a significant problem in some cities, it is likely a secondary concern when compared with cities just trying to find water.

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