Superstorm Sandy did not flood downtown Boston — but it could have. Had the storm arrived six hours earlier, at high tide, water would have surged through city streets. And of course, had the storm’s center struck Boston — and in particular, had it done so at high tide — the damage to Boston could have been on a scale matching the destruction that actually occurred at Sandy’s peak in New York City.

In actuality, Sandy didn’t bring destructive flooding to the Boston area. But a nor’easter three months later did flood nearby towns: “In Salisbury, a storm surge of at least 20 feet rolled over the seawall, prompting evacuation of dozens of residents. In Winthrop, waves breached a seawall, sending torrents of water down streets in the Point Shirley neighborhood and flooding cars and basements. And in Scituate, water poured onto Ocean Avenue and surrounding streets, spurring frantic calls from residents trying to get out,” the Boston Globe reported on February 9 (“Ocean surges over seawalls; National Guard dispatched to coastal communities,” by Stephanie Ebbert).

Flooding of a few beachfront streets is an emergency. Major flooding of large portions of downtown Boston could be a catastrophe. And it’s an increasingly likely prospect, city planners warn. Boston, like many old East Coast port cities, lies low to the waterline, and is partly reclaimed from the sea — built in large part on artificial fill deposited in the bay. And like other East Coast cities, Boston faces a future that is complicated by the rising level of the ocean — the city’s lifeblood, and also potentially its greatest foe.

In a February press conference, Boston Mayor Thomas Menino announced a combined public-sector and private-sector push to make the city more resilient in the face of future flooding, the Globe reports (“Boston prepares for climate change effects,” by Beth Daley). The goal is to “make our waterfront and the rest of Boston better prepared to handle future storms and get the city back in business as quickly as possible,” Menino said.

Also in February, the Boston Harbor Commission released a report comparing the storm-surge flood risk to Boston and vicinity at current sea levels with the risk that will come about from storms similar to Sandy if sea levels rise by 2.5 feet as predicted during this century (“Preparing for the Rising Tide”). If a storm like Sandy were to strike at high tide after a 2.5-foot rise in sea level, most of Boston and surrounding communities such as East Cambridge and Brookline would be flooded with seawater, the report says (see maps).

The Atlantic has this report on the Boston Harbor Association study: (“These Scary Maps Explain What Sea Level Rise Will Mean in Boston,” by Emily Badger). “ If average sea levels rise by 5 feet – a possibility by the year 2100 – today’s 100-year flood would become the city’s new normal, occurring twice a day at high tide,” notes The Atlantic. “At that sea level, a moderate storm surge of another few feet could inundate 30 percent of the city.”

Of course, projected rises in sea level are just a possibility, not a certainty. And a perfect storm that nails any city right at high tide is also, at worst, an occasional risk. But parts of Boston’s low shoreline already flood during routine storms. And what Boston planners are advocating isn’t that the city jump instantly to a state of readiness appropriate for a 100-year storm surge event, 100 years in the future. Instead, they’re suggesting that developers, builders, and property owners make incremental adjustments in response to gradual changes — but that they do so early enough to get ahead of the curve.

Brian Swett, Boston’s Chief of Environment and Energy, points to examples from New York City, reports the Globe: “That city added a step up to get in subway stops in places, adding 6 inches of flood protection. City officials also examined air vents, which are often at street level, and raised some of them higher.”

Vivian Li, one of the authors of the Preparing for a Rising Tide report, told the Globe, “we can phase it in over two, three decades. It’s not that you have to do it [immediately], but to think and plan for it.”

More Coverage: “Boston Grapples With The Threat Of Storms And Rising Water,” by Christopher Joyce (NPR).

“Boston In the Year 2100 Looks Really … Wet,” by Rosemary Chandler (Boston Daily).