Fire Weather: On the Front Lines of a Burning World

by John Vaillant

When you consider the vast quantities of water flowing and filtering through the boreal forest, and the fact that Fort McMurray is located at the confluence of not two but four rivers, in close proximity to numerous lakes, creeks, and muskeg bogs, it seems counterintuitive that the air could be as dry as Nevada’s, but this is the reason Alberta’s sky is so famously clear: because the air has so little moisture in it. It has so little moisture, not because of where that air is, but because of where it comes from. This parched air, a feature of the region’s high-pressure systems, flows in from the north. “North,” in Alberta’s case, is a polar desert known as the Northern Arctic Ecozone. Comprising most of the Canadian Arctic, all the way to the North Pole, it is one of the driest places on Earth. The injection of desert-dry Arctic air, combined with the day’s unprecedented temperatures, created ideal conditions for the rapid and sustained evaporation of all surface moisture. That morning, the relative humidity had dropped from 30 percent to less than 20 percent in under an hour, and it had yet to bottom out.