RIDEAU CANAL, OTTAWA

Before we look forward, let’s instead look back: after the War of 1812, British military forces in Ottawa felt vulnerable to American invasion along the St. Lawrence River. The waterway from Montreal to Kingston needed to be both protected and controlled. The solution was to build the Rideau Canal with its now-famous locks, still in operation in Canada’s capital.

To live in a city plagued with alternating droughts and floods, Ottawa residents will need that same resourcefulness in 2100, notes Frank Seglenieks, water resources engineer with Climate Change Canada. Count on seasonal sea-ice cover in the Hudson and James bays to decline as sea levels rise, but the best prediction for the future state of the Great Lakes is that they’ll be entirely unpredictable. “It’s not intuitive,” says Seglenieks, “because people want to hear there’ll be [either] more or less rain, but the truth is these weather systems will bring increased flooding and droughts, back and forth.” Seglenieks has seen this happening already in the region: Lake Huron’s water level was the lowest in recorded history in 2013, while Lake Ontario reached its highest level just four years later.

Ottawa will have to do better than just survive floods—it’ll have to become a city that both moves and floats to accommodate changing weather patterns. “This is going to take a whole lot of planning, and we should be thinking about it already,” he says. For example, say you’re building a dock. “Instead of building it solidly along the shore, you’re going to build a floating dock that moves up and down.” The same could be true for houses, which should be carefully constructed to treat floods not as a fluke but as the new norm. If Seglenieks were building his dream house in Ottawa, he’d stay far from the unpredictable river. “I’d look for the highest that the river has ever been in recorded history. Then I’d build even higher than that.”