19How cities are adapting to a changing climate

The short version: Cities built at the water's edge are planning for seas that are already rising, heavier rain and hotter summers, while also trying to cut the emissions from their own buildings. Boston's 2016 Climate Ready Boston study set its baseline: up to roughly 1.5 feet of sea level rise by 2050 and at least 3 feet after 2070, with today's 1-in-100-year flood becoming a 1-in-10-year flood after mid-century. The responses range from raised parks and flood barriers to rules for building emissions.

How much will sea levels rise in Boston?

The planning numbers come from Climate Ready Boston, a city study released in December 2016.⁴² Secondary reports of it give slightly different ranges, so here is what each says:

• The Barr Foundation's summary: sea level rise of roughly 7 inches to 1.5 feet by 2050 regardless of future emissions, and at least 3 feet after 2070.⁴²
• CommonWealth Beacon's account: a most likely rise of 7.5 to 18 inches by 2050, with a maximum plausible rise of 30 inches; and roughly 3.2 to 7.4 feet by 2100 depending on emissions, with a maximum plausible rise of 10.5 feet.³⁸³
• The Dorchester Reporter's account: 9 inches of rise in the 2030s at Columbia Point and 1.5 feet above 2000 levels by 2050.¹⁰⁰

In metric terms, 1.5 feet is about 46 cm, and 3 feet about 0.9 m. Sea level along coastal New England is rising faster than the global average.³⁸³

The Barr summary describes the 2050 range as holding regardless of future emissions.⁴² The figures after 2070 depend heavily on how much the world emits between now and then.³⁸³

For design, the city uses fixed numbers. Boston's Climate Resilient Design Standards for public rights-of-way plan for 9 inches of sea level rise for structures in place through 2030, 21 inches through 2050, and 40 inches through 2070.³⁸⁴ The 40-inch figure recurs in later city projects: Boston's Resilient Moakley Connectors page, updated in July 2026, describes Moakley Park as a major flood pathway under 40 inches of sea level rise.³⁸⁵

What is a 100-year flood?

A 1% annual-chance flood, often called a "100-year flood," is a flood with a 1-in-100 chance of happening in any given year. The name misleads people: it does not mean once a century, and two can happen in back-to-back years.

Sea level rise changes the odds. Climate Ready Boston found that today's 1% annual-chance waterfront flood would become a 10% annual-chance flood after mid-century.⁴² For scale: over 30 years, a 1% annual chance adds up to roughly a one-in-four chance of at least one such flood. At 10% a year, at least one becomes close to certain, and more than one is likely.

Exposure grows with it. By about 2070, roughly 85,000 people and $85 billion of property would be exposed to flooding.⁴² In Dorchester alone, "as soon as the 2070s," about 4,500 structures could flood in a low-probability event, causing $86 million in direct physical damage.¹⁰⁰

Why not build one big sea wall?

A single barrier across Boston Harbor would likely cost more than $10 billion.¹⁰⁰ Instead, Boston's planning assumes the city "will require multiple layers of flood protection."³⁸³ In practice, that means defending low spots where water would enter, raising parks and roads at those points, and changing how buildings near the water are built, rather than relying on one wall.

The low spots matter because floodwater follows the ground. Land around Moakley Park and Interstate 93 in South Boston is low-lying and creates a path for floodwater toward South Boston, the South End and Roxbury.¹⁰⁰ So a flood barrier at a waterfront park can protect neighborhoods well inland, which helps explain why parks have become flood infrastructure in Boston's plans.

As of fall 2025, the plan for Moakley Park centered on a 2,500-foot landscaped berm meant to protect the park, neighborhoods and evacuation routes, with a state environmental (MEPA) filing expected in October or November 2025.³⁸⁶ A related city project for the areas north and south of the park lists 2026 as its expected completion year and held community meetings in November 2025 and June 2026.³⁸⁵

In East Boston, the city installed a deployable flood barrier on the Mary Ellen Welch Greenway in 2018, a measure first identified in the 2017 Coastal Resilience Solutions report for East Boston and Charlestown; it blocks a surge path under Sumner Street and protects almost 4,300 residents.³⁸⁷ A separate Greenway rebuild is expected to be under construction until about December 2026.³⁸⁷

How it changed

Boston's planning grew out of a design exercise before it became policy. The Boston Living With Water design competition, launched in 2014, drew about 50 entries from seven countries.³⁸³ Teams redesigned real sites to "continue to thrive once sea levels are five feet higher than today."³⁸³ The city also exchanged ideas with experts from Copenhagen, the Netherlands and Hamburg, according to CommonWealth Beacon, which gives no further detail.³⁸³

Climate Ready Boston followed in December 2016.⁴²

Those foreign exchanges point to cities that are often cited as models.

Rotterdam's Benthemplein water square, opened in December 2013, collects rainwater in sunken basins during heavy storms to ease pressure on the sewers; its sunken sports area floods only in extreme rain and dries out for play afterward.³⁸⁸ Copenhagen drew up its Cloudburst Management Plan in 2012 after a 2011 cloudburst caused more than 6 billion Danish kroner in damage. The plan combines a larger sewer network with about 300 surface projects that hold or channel water.³⁸⁹

In the US, New York's East Side Coastal Resiliency project is a $1.45 billion, 2.4-mile flood barrier on Manhattan's Lower East Side, which rebuilds East River Park 8 to 10 feet higher than before.³⁹⁰ Sections opened in stages from 2022 to 2025, and the city expects the full park to reopen in early 2027.³⁹⁰ The project drew strong opposition. In 2020, groups including East River Park Action sued, arguing it would cut the park off from the neighborhood, and a state judge ruled against them. Critics also objected to the loss of more than 1,000 mature trees and the long park closure, and proposed barriers along the FDR Drive instead.³⁹¹

Flooding from the sky, not only the sea

Coastal flooding is one threat. Heavy rain is another, and it hits places nowhere near the shore when storm drains cannot keep up. The ASCE's 2025 report card gave US stormwater infrastructure a D, among the lowest grades of any category.³⁷¹ In Boston, storm drains belong to the Boston Water and Sewer Commission, which runs about 1,435 miles (2,310 km) of sewer and storm drain pipe.⁴⁴ (How that network works is in Where it goes after you flush (or it rains).)

Pipes sized for the rainstorms of past decades can be overwhelmed by heavier downpours, and replacing them street by street is slow and expensive. That is one reason cities are turning to parks, plazas and other surfaces that can hold water for a few hours.

What about heat?

Cities run hotter than the surrounding countryside because pavement and roofs absorb sun and there is less shade and vegetation; this is called the urban heat island effect. Responses usually include tree planting, lighter-colored roofs and pavement, and cooling centers opened to the public during heat waves.

Boston's plan is Heat Resilience Solutions for Boston, released in spring 2022, which sets out 26 citywide strategies and targets five neighborhoods: Chinatown, Dorchester, East Boston, Mattapan and Roxbury.³⁹² When the mayor declares a heat emergency, Boston Centers for Youth & Families (BCYF) community centers open as cooling centers during their normal hours, as in August 2025.³⁹³

Cutting building emissions

Adaptation is half the picture. The other half is cutting emissions. In cold-climate cities, buildings are a natural target, because heating them burns fuel for much of the year. Rules for new buildings are covered in The rules for building in a city.

Boston's main tool for large existing buildings is an ordinance known as BERDO. First passed in May 2013, it originally required large buildings to report their annual energy and water use.³⁹⁴ A 2021 amendment, approved unanimously by the City Council, added emissions limits for non-residential buildings of 20,000 square feet or more and residential buildings with 15 or more units. The limits begin in 2025 or 2030 depending on building size and reach net zero by 2050.³⁹⁴

In Boston

Pulling the verified pieces together for Boston as of October 2026:

What's changing now (2026)

The project updates above show Boston's Moakley Park and East Boston work still in design or construction in 2026. Two pressures covered in Who pays for the city bear on it. US federal infrastructure money is less certain, with the 2021 infrastructure law's program authorities reaching their expiry date on September 30, 2026.³⁷⁰ And Boston's FY27 budget grew at its slowest rate since FY10.³⁵⁸ Our reading: resilience projects compete for the same capital dollars as schools and roads, and both pressures make that competition harder.

Report an error in this section