Knowing Your Flood Risk

Boston is among the most vulnerable cities in the country to flooding. As sea levels rise, damaging floods will become more common along the city’s coastline and rivers. But the risk is not limited to coastal areas. Inland flood risk is increasing with more frequent and intense precipitation that could overwhelm the city’s stormwater system.

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If you're experiencing a flood and need emergency help for life- or property-threatening issues, please call 9-1-1. Visit the Flood Safety Tips page, Recovering from a Flood page, and the Boston Public Health Commission’s Environmental Health and Hazards page for additional resources.

Flood Risk

NWS-NOAA graphic showing storm surge, a rising of the sea as a result of atmospheric pressure changes and wind associated with a storm.

Coastal Flooding

Coastal flooding is caused by sea level rise, seasonal high tides, and storm surge. Storm surge is a rise in sea level that occurs during a storm, caused by strong winds pushing the water towards the shore. As sea levels rise and intense storms become more frequent, low-lying areas along Boston’s 47 miles of coastline will become more vulnerable to flooding.

Riverine Flooding

Boston has four main rivers, the Charles River, the Neponset River, the Mystic River, and the Muddy River, as well as several brooks, creeks, ponds, and a reservoir. Many of the rivers have flood control systems that lessen the likelihood of major damage. However, minor-to-moderate flooding has occurred along Boston’s rivers, causing damage to homes, businesses, institutions, and the public transit system.

Stormwater Flooding

The Boston Water and Sewer Commission (BWSC) maintains the city’s stormwater system that captures runoff from rain or snow in more than 30,000 catch basins. The runoff is transported through nearly 600 miles of drain pipe to more than 250 stormwater outfalls, where it discharges into one of several Boston water bodies. Heavy rainfall can overwhelm stormwater systems, causing flooding on roads and properties. In the coming decades, rising sea levels and more intense precipitation and coastal storms will stress the city’s stormwater system, increasing the risk of flooding. Visit BWSC’s Resilience Hub to learn more.

The Massachusetts Department of Transportation (MassDOT) and the Massachusetts Department of Conservation and Recreation (DCR) own and manage several highways, bridges, tunnels, major roadways, parkways, and culverts in Boston, including the stormwater drainage system below street level. Although BWSC manages most of the city's stormwater, MassDOT and DCR operate independent systems, such as catch basins and outfalls connected to the roads they own.

Report street flooding to 9-1-1. If you see a catch basin that needs to be cleared, please contact 3-1-1.

Flood Maps

Discover your property's flood risk.

View the Flood Maps

FEMA FLOOD ZONES

The Federal Emergency Management Agency (FEMA) maintains flood maps to help communities understand their flood risk. Areas shown on the FEMA flood map with a 1% or higher chance of flooding in any given year have a one-in-four chance of flooding during a 30-year mortgage. FEMA flood maps are used to determine rates under the National Flood Insurance Program. Visit the Flood Insurance page to learn more.

Moderate-to-Low Flood Risk: Zones C and X, unshaded, are at a lower risk of flooding, though not entirely without risk.
Moderate Flood Risk: Zones B and X, shaded orange, are areas that may have reduced their risk with mitigation efforts such as levees or experience shallow flooding, with water usually less than 1 foot deep or covering less than 1 square mile.
High Risk: Zones A, AE, AH, AO, AR, and A99, shaded teal blue, are high-risk flood areas due to proximity to a pond, stream, river, or protective barrier under construction.
Higher Flood Risk: Zones V and VE, shaded teal blue, are high-risk coastal areas with an additional hazard from storm waves.