New Study Finds One in Five NYC Blocks Sits on Former Wetlands as Flood Risks Rise

More than a fifth of New York City sits atop land once covered by water—portending mounting flood risks as climate change advances.

Four centuries ago, Manhattan and its neighbouring boroughs were little more than glaciated swamps, meandering creeks and brackish inlets—a watery patchwork that proved irresistible to developers with shovels and dreams. Today, a startling new analysis suggests that the city’s aquatic past is far from buried. Researchers at the New York Botanical Garden, whose staff are better known for cultivating orchids than predictive datasets, have mapped New York’s so-called “Blue Zones”: more than 20% of city land where water once pooled, water now floods, and where—thanks to accelerating climate change—flooding will likely define large swathes of the urban future.

The findings, published this week in the Annals of the New York Academy of Sciences, quantify the scale of the threat with uncommon precision. Using historical maps, contemporary flood records and climate modelling, the researchers identified over 500 Blue Zones scattered throughout the five boroughs. Some are as predictable as Coney Island or Jamaica Bay; others lurk beneath the concrete in neighbourhoods few would see as watery, like East Harlem or Gowanus.

The implications are as expansive as they are sobering. Fully 1.2 million New Yorkers—around 12% of the city’s population—now reside in these Blue Zones, alongside 11% of buildings. A third of all public housing developments are perched atop former marshes, streams or tidal flats, putting some of the city’s most vulnerable residents directly in water’s path.

Eric Sanderson, a vice president at the Botanical Garden and a lead author of the study, concedes he, too, was startled by the overlap between history and modern peril: “Places that were wet, are wet, and will be wet in the future.” This recursive wetness is of more than academic interest. The city has been battered in recent years by high-profile inundations: in 2021, the remnants of Hurricane Ida dumped record-breaking rainfall, overwhelming sewers and killing 13 people in basement apartments. In contemporary New York, a millennia-old streambed is no longer an archaeological curio but a flood hazard with human costs.

If city planners and policymakers needed a map for prioritising resilience, this new study hands it to them, block by block. The Botanical Garden’s team built a digital tool that visualises each Blue Zone by historical ecology, current flood vulnerability and projected future risks. It is, conceptually, both a warning sign and a Rosetta stone for where adaptation—hard infrastructure as well as green—will be most urgent.

First-order ramifications abound. Both LaGuardia and JFK airports, serving tens of millions of passengers annually, sit on land reclaimed from former salt marshes—making them exposed to storm surges and sea-level rise. The problem is not confined to showpiece infrastructure: schools, hospitals, and a panoply of utilities all find themselves in similar soggy company.

The second-order effects could prove even more profound. As flooding grows more frequent—by mid-century, the National Oceanic and Atmospheric Administration reckons, New York could see up to two feet of additional sea level—insurance costs are set to swell. The consequence: higher rents and mortgage rates, diminished property values and, inevitably, the fraying of delicate social fabrics, particularly in lower-income districts. Already, flood-prone areas like the Rockaways and East New York have seen increased financial burdens fall disproportionately on renters and public housing tenants.

Politically, this data may fuel the perennial row over who pays for adaptation. The city’s capital budget for coastal resilience projects, like the East Side Coastal Resiliency Project (currently running to $1.45 billion), seems puny when set against the sheer acreage at risk. Nor is the private sector inclined to swallow mounting insurance losses with good cheer; expect insurers, and their allied lobbyists, to make their presence felt in Albany and City Hall alike.

A glance beyond New York reveals these troubles are by no means unique. Miami’s downtown gleams atop land similarly prone to submersion, whilst Boston, Houston and even parts of London have all been compelled to reconsider developments built over vanished wetlands or infilled marshes. The difference is New York’s density: nearly 30,000 souls per square mile, a concentration that magnifies both risk and required resilience.

A chance to reimagine, not merely react

The question now is whether New York will merely brace against water, or finally begin to live with it. The temptation has long been to pour more concrete, sculpt bigger berms, and hope the next deluge waits another decade. But the Blue Zones study suggests a different, more nimble approach might be needed. Adaptation, to be effective, must borrow from both Dutch ingenuity—room for the river—and local know-how: restoring marshes where possible, daylighting buried streams, and developing policies that incentivise (rather than punish) resilience in housing and insurance markets.

We reckon that the city would do well to take the Botanical Garden’s map as an opening bid, not a closing argument. Its level of granularity can foster sharper zoning, smarter investment and, paradoxically, more imaginative uses of public land. Instead of merely raising seawalls, why not design parks that double as floodplains, co-opting water rather than treating it as a syrupy foe?

There is a certain poetic justice in the idea that the city’s glitzy present is carried, quite literally, by its sodden past. Migrations, real estate speculation, and human ingenuity have long tried to outpace nature’s damp reminders, yet the water tends to have the last word. As climate change accelerates, the cost of ignoring those voices grows steeper.

Still, if city agencies and ordinary New Yorkers are prepared to heed the data—and to ask difficult questions about who gets protected, at whose expense—the Blue Zones then offer more than foreboding. They present an opportunity to imagine a New York that is not merely drier, but fairer and wiser, one that acknowledges the persistence of water underneath all the pavement and promise.

Whether New York can summon the funds, political will and architectural creativity to adapt remains to be seen. But as every student of the city’s history knows, tides—like times—rarely stand still. ■