Canada, according to current predictions, may not suffer from lower rainfall when temperatures rise. But as Walt Kelly said, "When you starve with a tiger, the tiger starves last." Canada must share water with the US - morally, and because we won't have any choice.
Bulk water export is currently illegal in Canada. At a lecture I attended recently, Canadian civil servant Peter Boehm hinted that the Harper government is planning to rescind that law. But even if we hold out on prohibiting bulk water exports, there are lots of ways the US can get water - the US has a lot of shore line on the Great Lakes and St. Lawrence, for a start.
Gwynne Dyer thinks that, other than some cottage owners on the Great Lakes, Canadians won't be hurt by sharing our water with the United States. He says the US could keep a couple of supertankers in the mouth of the Skeena River, scoooping up fresh water before it flows into the Pacific Ocean, as well as divert Great Lakes water, and that he doubts it will resort to reversing the direction of rivers. He cautions that Canada will be better off if we keep control of the situation - otherwise the US may declare water a national security issue and take it by force.
What I worry about is not the diversion of needed water to the US. Of course if we have water and the US needs it then we should share. My concern is the diversion of Canadian water to ridiculous over-consumption in the US. The US already diverts water to grow rice in arid areas and to allow golf courses in the desert. I have seen huge sprinklers in Arizona watering a grassy median on a hiway surrounded by desert. I'm afraid it's going to feel like rape and plunder.
The issue of the US taking our water is a passionate one for Canadians. It was one of the most oft-heard concerns during the negotiation of the Free Trade Agreement, and is the reason that we passed a prohibition on bulk water exports. It isn't going to be an easy thing to give up.
In the meantime, here's something to think about: "Mandatory or voluntary water restrictions were placed in effect in parts of Florida, Texas, Oklahoma as lake and reservoir levels dropped and other municipal water supplies were reduced. River transportation was severely curtailed because of low levels of the Missouri and Mississippi Rivers and their tributaries. Agricultural impacts of drought include farmers being driven out of business and hay shortages in Wyoming, and low crop yields in Colorado, South Dakota, Missouri and Alabama. Wildlife population declines were noted in Arizona, Oklahoma and South Dakota." That was issued by the National Climactic Data Center in November.