The more you follow government down to the local level, the harder it is for decision-makers to pretend climate change isn’t real. Coastal cities in particular can see what’s coming, and their officials understand that people can’t just sit on their hands. When you’ve cleaned up after storm surge flooding before, the risk of more severe flooding feeds a concrete urgency. One of the first cities to get the ball rolling was Boston, which recently released a new report laying out a roadmap for a “Climate Ready Boston.”

The report was prepared by a team of city officials, planning consultants, non-profits, utilities, and climate scientists. The scientists provided climate projections for the Boston area, and the others analyzed the city for vulnerabilities to those expected changes.

For several scenarios of future greenhouse gas emissions, the report summarizes the possible range of increases in hot summer days, extreme precipitation, and sea level and flooding events along the coast or in areas with poor drainage.

The number of heat-related deaths, for example, is expected to grow as the frequency of heat waves increases. Damage from flooding, too, will increase as the climate warms. Around the middle of the century, the report projects that about seven percent of the city could be under water during one-in-10-year rainstorms unless the storm water system is improved. That includes portions of the subways and major highways, some of which are designated evacuation routes.

While rising sea levels do threaten to simply inundate some areas around the harbor, they also limit the effectiveness of drainage systems, which function based on the lower elevation of ocean water. For a sea level rise just short of two feet, the report estimates annualized losses of about $455 million per year from flooding damage—growing to $1.39 billion per year at three feet of sea level rise.

By identifying the exact areas of the city vulnerable to this flooding, the authorities can see where drainage systems or other infrastructure—like the electric grid—will need to be improved or protected. And by identifying the populations most vulnerable to heat waves or flooding, the city can be mindful of how to best help its people.

Much of the report lays out a framework to organize future plans of action and a laundry list of tasks to complete. It highlights some of what it calls "resilience principles,” like taking advantage of regularly scheduled construction work to build in these improvements, designing infrastructure to be flexible enough to handle future conditions, and making sure that projects are valuable for more than just one purpose. It's possible to do things like providing useful public space that serves as flood protection, for example.

For some specifics, the report singles out eight Boston neighborhoods for closer analysis. Charlestown, for example, was largely built on fill at the water’s edge. The report states that half of Charlestown would be exposed to coastal flooding during a 100-year storm before the end of this century. There are subway stations, hospitals, storm sewer lines, and power plants that would be affected. Improved flood protection is suggested at two points: a dam on the Charles River that could be overtopped and a low point where seawater could flow in unless some sort of barrier is added.

The report also calls for feasibility studies of flood control options across the entirety of Boston Harbor. That could include modifying the mouth of the harbor to dampen the tides or a barrier that could go up to defend against storm surge flooding. Structure like that would be pretty expensive—but less expensive than a flooded city. That’s the math for coastal cities in the 21st century.