WASHINGTON — Crippling heat waves are an annual fixture in the United States — but it’s not every day the White House announces a detailed strategy to confront them. So far, it’s been an extreme-weather summer across the continent: brutal heat, a barrage of tornadoes, flooding in the U.S. northeast and an unprecedented wildfire season in Canada. This weekend in the U.S. promises to be no different, with temperatures in California’s record-setting Death Valley predicted to reach a scorching 52 C. That’s why the Biden administration is introducing what it calls an “all-of-society response” to help manage a challenge it says is only getting worse. In Ottawa, the federal government is also getting ready with a strategy geared towards helping the most vulnerable, including older Canadians, Indigenous communities, inner-city residents and people who work outside. …Experts in both countries have been pushing their governments to define sustained periods of extreme heat as a natural disaster.