As my airplane flew low over the flatlands of western Michigan on a dreary December afternoon, sunbursts splintered the soot-toned clouds and made mirrors out of the flooded fields below. There was plenty of rain in this part of the Rust Belt—sometimes too much. Past the endless acres, I could make out the eastern shore of Lake Michigan, then soon, in the other direction, the Detroit River, Lakes Huron and Erie, and southern Canada. In a world running short on fresh water in its lakes and rivers, more than 20 percent of that water was right here. From a climate standpoint, there couldn’t be a safer place in the country—no hurricanes, no sea-level rise, not much risk of wildfires. That explains why models suggest many more people will soon arrive here. My destination was the working-class city of Ypsilanti, and a meeting with Beth Gibbons, an urban planner and specialist in climate adaptation. Gibbons served as the founding executive director of a planning consortium called the American Society of Adaptation Professionals (ASAP), which was formed …