What is the Risk?
Vulnerability to flooding varies across New York City. Different neighborhoods face different risks. Risks are primarily determined by flood type, the number of people and types of property or infrastructure that are most exposed to flooding, the degree of exposure to floods, and how well the people and the built environment can withstand damage.
Flooding’s immediate and long-term impacts can include:
- Loss of life, injury, and illness
- Aggravation of existing health conditions
- Psychological effects such as depression and anxiety
- Disruption of critical infrastructure systems, including transportation, energy, telecommunications, and wastewater
- Water pollution as a result of combined sewer overflows and the release of hazardous materials from flooded industrial sites
- Loss of income for individuals and of revenue for businesses
- Disruption of communities and social networks
- Disruption of open space, parks, and recreational amenities
Of New York City’s more than 8.2 million residents, less than 5 percent, or approximately 400,000 people, live within the 1 percent annual chance floodplain and are at greater risk of coastal flooding hazards.
Population and Households in 1 Percent Annual Chance Floodplain
|New York City||Bronx||Brooklyn||Manhattan||Queens||Staten Island|
In New York City, vulnerable populations include children, seniors, low-income residents, the "linguistically isolated" (those who speak English less than “very well”), people with disabilities and other access and functional needs or other pre-existing health conditions, and in-patient populations at hospitals and other healthcare facilities.
To illustrate the potential impact of a flood on vulnerable populations, the sections below closely examine the potential impact of a flood hazard on people over the age of 65 and others living below the poverty line.
A person’s age plays a central role in determining their ability to take actions that will reduce their risk in an emergency. New Yorkers in the 65-plus age group—approximately 12 percent of the city’s total population—are among the most vulnerable during a flood-related disaster. As a group, seniors are more likely to have health conditions and disabilities that require regular access to health services and medication. During major flooding events, these services are often disrupted or severely restricted.
For seniors, decreased mobility can prevent timely evacuation or movement to safer ground. In the aftermath of a flood, exposure to mold in flood-damaged buildings can have a more severe impact on older people, particularly if they have respiratory infections, asthma, allergies, or other pre-existing health conditions.
Flood-risk vulnerability is acute among immigrant seniors. Almost 49 percent of New York City's older residents are foreign-born. Compared to native-born seniors, older immigrants often earn lower wages, have less in retirement savings, and receive fewer benefits from traditional entitlement programs like Social Security and Medicare.
Today, people in the 65-plus age group represent over 6 percent percent of New York City’s population, or approximately 67,188 people, living in the 1 percent annual chance floodplain shown on PFIRMs. Since the city's older adult population is growing more rapidly than the overall population, the vulnerability of seniors to flooding risk is likely to increase in the future.
Population by Age Group within 1 Percent Annual Chance Floodplain
|New York City||Bronx||Brooklyn||Manhattan||Queens||Staten Island|
|Under 5 - total||555,383||107,454||193,851||82,024||144,634||27,420|
|Under 5 in PFIRM||23,585||1,029||9,278||4,400||7,067||1,811|
|% under 5 in PFIRM||4.2%||1.0%||4.8%||5.4%||4.9%||6.6%|
|Under 18 - total||1,793,861||367,431||608,639||239,355||472,878||105,282|
|Under 18 in PFIRM||80,191||4,191||31,746||13,675||23,729||6,850|
|% under 18 in PFIRM||4.5%||1.1%||5.2%||5.7%||5.0%||6.5%|
|Age 65 and over - total||1,099,330||161,923||317,575||235,172||315,853||68,807|
|65 and over in PFIRM||67,188||2,488||32,645||12,515||15,157||4,383|
|% 65 and over in PFIRM||6.1%||1.5%||10.3%||5.3%||4.8%||6.4%|
Source: US Census, 2012-2016 American Community Survey—Summary File allocated by Census 2010 block level population.
Low-income communities are disproportionately affected by almost all disasters, including floods. A flood can damage and/or destroy homes, businesses, and inventory. Floods can also damage critical infrastructure and disrupt vital services.
Low-income households have fewer resources at their disposal to prepare for and recover from flooding disasters; therefore, compared to other population groups, this segment faces greater health and safety risks and economic hardships. New York City defines the low-income segment of the population as a one-person household earning $11,500 or less and a four-person household earning $23,000 or less. Approximately 19 percent of those living in the 1 percent annual chance floodplain according to the PFIRMs—or approximately 79,000 people—are estimated to live below the poverty level.
|Population below Poverty Level within 1 Percent Annual Chance Floodplain|
|Percent Below Poverty Level|
|New York City||19.4|
|Source: US Census, 2012-2016 American Community Survey, Summary File.|
A significant percentage of low-income households in New York City are renters, who have little control over repairs if their buildings are damaged. Of the more than one million New Yorkers making less than $30,000 per year (roughly 60 percent of the median income in New York City), 82 percent are renters, compared with 18 percent who are owners.
With the high cost of housing in New York City, finding alternative housing options—even temporarily during an evacuation or immediately following a storm—can pose a serious challenge. A New York City Department of City Planning (DCP) study found that citywide, about 36 percent of owner-occupied homes with mortgages in the floodplain were housing cost-burdened and about 41 percent of renter-occupied floodplain households were housing cost-burdened.
Even in ordinary times, the housing that households earning under $30,000 per year can afford is limited to just 22 percent of New York City’s total rental units. After a flood, many low-income individuals and families continue to occupy their damaged homes to avoid paying an increased share of income towards rent or to avoid homelessness.
The practice of occupying otherwise uninhabitable residences post-flood can increase the vulnerability of low-income households in other ways, such as increasing residents’ exposure to mold and other hazardous materials. Health problems, in turn, can result in lost wages or even loss of employment, further increasing these households’ economic vulnerability.
Considerations of geography, land use, and the density of built assets that are exposed to flood risk are all factors that are used to assess a particular property’s vulnerability. This section examines:
In New York City, the land use, waterfront characteristics, and building stock create a complex environment. Dense commercial and residential areas line the Hudson and East Rivers. Industrial districts line the Long Island Sound and New York Harbor. Residential neighborhoods abut oceanfront beaches. Different areas have different building types, and each face unique risks.
Flood risk varies by building height, construction type, construction materials, and age. In general, low-rise buildings (one to two stories) are more vulnerable to structural damage than mid-rise (three to six stories) and high-rise (seven stories or higher) buildings. Low-rise buildings tend to house primary uses on the ground floor and therefore face a higher risk that they will sustain substantial damage. Low-rise buildings also tend to be constructed with lighter, wood-stud frames, which are more prone to structural damage from flooding.
Wood homes are at higher risk from fires generated by electrical shorts than homes built with steel, masonry, or concrete frames -- characteristic of larger, more recent building types. Although wood buildings are less expensive to repair, reconstruct, and elevate than masonry buildings, new wood-frame housing is not permitted in most areas of New York City.
Older buildings are more likely to sustain significant flood damage than newer buildings primarily due to the increasingly stringent building and zoning standards that have been instituted over time. Adherence to flood-resistant construction standards greatly reduces vulnerability to flood damage. Data is limited on buildings’ elevation and floodproofing characteristics, so a building’s age is the best indicator of its structural vulnerability.
Roughly 67,600 buildings are located in the 1 percent annual chance floodplain.
The following chart shows the percentage of buildings within New York City’s 1 percent annual floodplain classified according to the size, material, and age.
Building Type and Age within 1 Percent Annual Floodplain
|1 Floor||2 Floors||3-6 Floors||7 or more floors||Other||Grand Total|
Source: MapPluto 13V1; FEMA, PFIRMs
These buildings represent substantial economic value and occupy important roles in the community -- homes, offices, schools, and hospitals. Approximately 175,000 residential units, home to over 400,000 New Yorkers, are located within the 1 percent annual chance floodplain.
New York City’s infrastructure is also vulnerable to flood risks, which can disrupt critical systems, such as transportation, energy, telecommunications, and wastewater.
The table below shows the vast number of critical assets located within the 1 percent annual chance floodplain in New York City, which have a 1 percent or greater chance of being flooded in any given year.
Critical Assets in the 1 Percent Annual Chance Floodplain
|Critical Asset||Number of Assets in 1 Percent Annual Chance Floodplain||Percentage of All NYC Assets in 1 Percent Annual Chance Floodplain|
|Subway stations (includes PATH stations)||27||5%|
|Bridges and tunnels||32||43%|
|Major roads (miles)||158||18%|
|Emergency services – police stations||2||3%|
|Emergency services – fire stations||16||7%|
|Emergency services – EMS stations||9||11%|
|Educational – colleges||4||3%|
|Educational – public schools||74||5%|
|Educational – private schools||28||3%|
|Healthcare – hospitals||4||5%|
|Healthcare – nursing homes||14||8%|
|Healthcare – hospice||1||1%|
|Healthcare – adult healthcare centers||14||18%|
|Infrastructure – power plants||8||31%|
|Infrastructure – wastewater treatment plants||7||50%|
Much of the city's critical wastewater and waste management infrastructure is located in New York City’s 1 percent annual chance floodplain. These critical facilities were either sited along the waterfront out of operational necessity or were built there years ago during the development of the infrastructure network.
For example, all of the city's 14 wastewater treatment plants are located at low elevations along the waterfront in New York City, because situating them near the waterfront significantly reduced the cost and environmental impact of treating wastewater. Half of the city's wastewater treatment plants have assets in the 2015 Preliminary FIRM 1 percent annual chance floodplain, so they are vulnerable to inundation by storm surge.
If not properly adapted, the majority of New York City's wastewater treatment infrastructure is at risk of being damaged in severe storms or floods, which could lead to combined sewer overflows and contamination of the waterways. Floodwaters from a surge can cause significant damage both to wastewater management facilities and to the critical equipment they house. The corrosive impact of seawater on these facilities’ electrical systems has the potential to disrupt the power supply and potentially cause an overflow of either partially treated or untreated sewage into waterways.
Although not reflected in the table above, a significant share of both municipal and private solid waste management facilities, as well as other industrial facilities that store and use hazardous materials, are located within the 1 percent annual chance floodplain. Flooding at facilities with improperly stored hazardous materials and solid waste can cause dispersion of contaminants, with adverse effects on employees, nearby populations, and natural resources.
To facilitate their operations, many parts of New York City's transportation system, such as ferry terminals, are located near the waterfront. Some transportation assets are built in low-lying areas or even below sea level. Some rail and vehicular tunnels and many subway stations—which make up a significant portion of the city's transportation network—are located underground.
The West Side Highway, FDR Drive, and other roadways in New York City are particularly vulnerable to flooding because they are located along the coastline at low elevations.
According to the 2015 PFIRMS, a significant percentage of transportation assets are located in the 1 percent annual chance floodplain -- approximately 12 percent of the city's roadway networks, all of the major tunnel portals except for the Lincoln Tunnel, portions of both New York City airports, a variety of commuter rail assets, all three heliports, and numerous subway entrances and vent structures (principally in lower Manhattan). These assets are vulnerable to flooding from both coastal surges and heavy downpours.
Tunnel entrances that are in low-lying areas or in areas with poor subsurface drainage are particularly vulnerable to flooding. Examples of vulnerable infrastructure include the F train on Hillside Avenue in Queens and the 1-train in lower Manhattan.
Generally, heavy downpours pose only a moderate risk to roads and bridges, because although they may experience more frequent temporary floods, they typically do not sustain lasting damage.
New York City's vast network of impervious streets is also vulnerable to flooding from heavy precipitation, storm surge, or, as in the case of the Hamilton Beach and Broad Channel neighborhoods in Queens, high tides. Approximately 72 percent of New York City’s 305 square miles of land area consists of impervious surfaces.
Much of the city's underground electric and steam distribution systems and generating facilities are located near the coast, placing them at risk from storm surge and floodwaters. Approximately 88 percent of the city's steam generating capacity lies within the PFIRM 1 percent annual chance floodplain. In the electric system, 53 percent of in-city electric generation capacity, 37 percent of transmission substation capacity, and 12 percent of large distribution substation capacity are within the 1 percent annual chance floodplain. In the coming decades, projections of sea-level-rise indicate that there will be a growing number of electrical infrastructure facilities that will be at risk.
For New York City’s natural gas system, storm surge poses the biggest risk to the distribution infrastructure. Although flooding itself will not necessarily stop the flow of gas, service can be compromised if water enters the pipes. Low-pressure distribution systems are particularly vulnerable. Furthermore, flooding could disrupt critical communications infrastructure used for the gas distribution system, reducing the utility’s ability to manage the system infrastructure remotely and to maintain situational awareness of how the system is faring during the emergency.
New York City’s electricity and steam power generation is largely dependent on natural gas and liquid fuel. All power plants in New York City are dual-fuel capable, primarily running on natural gas, but using fuel oil as a backup. Any disruption to the gas transmission infrastructure or to the fuel supply chains can disrupt power and steam production. Given the location of key fuel terminals, pipelines, and refineries—and the importance of waterfront access to move fuels into New York City—the biggest risk to the liquid fuel supply is storm surge. Of the 39 terminals in the New York metropolitan area, nearly all lie within FEMA's 1 percent annual chance floodplain, as mapped on the 2007 FIRMs.
New York City's telecommunication services – telephone, wireless, internet, and cable – are vulnerable to flooding, particularly from storm surge. Telecommunications facilities are generally situated farther from the floodplain than other types of infrastructure, yet almost 13 percent of the city's critical telecommunication facilities lie in the 1 percent annual chance floodplain. Moreover, the telecommunications networks’ high dependency on the power network significantly increases the risk of service interruption during a flood.
Vulnerability to the Telecommunications infrastructure is projected to increase with climate change. For example, by the 2020s, the percentage of critical facilities in the 1 percent annual chance floodplain is expected to grow to approximately 18 percent; by the 2050s, the percentage is expected to climb to 24 percent. With up to 2.5 feet of sea level rise expected by the 2050s, the risk to critical central offices, which provide connectivity across major telecom services, including the two largest central offices serving southern Manhattan, is likely to increase.
FEMA’s HAZUS-Multi-Hazard (MH) flood model provides damage estimates based on the flooding depth for a given location. The model assumes that damages are a result of standing water, and does not account for damage that may be caused by water moving at high speed. The MH flood model is not the same as a storm surge model.
New York City’s analysis focuses on the impacts of the 1 percent annual chance flooding event (the “100-year flood”). This analysis used FEMA's PFIRMs published in January 2015, which contained the best available data to date.
Damages from flooding are categorized according to a percentage of total building replacement cost. These determinations are based on the depth of flooding in relation to the height of a building’s first finished floor.
As shown in this table, eighty percent of the buildings in New York City’s 1 percent annual chance floodplain are predicted to have damage based on the HAZUS-MH flood model output. The numbers are rounded to the nearest 100 buildings. Approximately 5.8 percent of these buildings are predicted to have significant damage to more than 50 percent of the structure.
HAZUS-MH Calculation of Approximate Number of Buildings Damaged from a 1 Percent Annual Chance Floodplain, by Borough
|County||Number of Buildings Damaged By Percentage of Total Replacement Cost||Total Damaged||% of Buildings Damaged in the 1 Percent Annual Chance Floodplain|
|1 - 10%||11 - 20%||21 - 30%||31 - 40%||41 - 50%||> 50%|
Source: NYCEM GIS, HAZUS, and Department of Finance (DOF).
Based on FEMA’s PFIRMs, the table and map below highlight the key findings from the HAZUS-MH run of the economic loss associated with a 1 percent annual chance flood in New York City. Loss values are calculated to the nearest thousand dollars.
A 1 percent annual chance flood affecting all five boroughs could cause nearly $50 billion in damage. More than 40 percent of the total damage would be to contents such as furniture, supplies, and other possessions. This is a major increase since the last time the team ran the model back in 2014 ($13.7 billion in damage). This difference can be attributed to higher property values due to the economic recovery from the recession, improvements FEMA made to the Depth Damage curve, and importing the updated 2015 PFIRMs.Due to the data available, this amount shows the 2018 assessed building value, and not replacement value. The highest damages are in Queens totaling $28 billion, followed by $9 billion each in Brooklyn and Manhattan.
HAZUS-MH Calculation of Direct Economic Losses from a 1 Percent Annual Chance Flood Flood, by Borough and Damage Type
|Borough||Structural Damage ($)||Contents Damage ($)||Inventory Loss ($)||Total ($)|
Source: NYCEM GIS, HAZUS, and Department of Finance (DOF).
The map shows the geographic areas of New York City where flood damage to buildings presents the greatest risk of economic loss from flooding. The largest areas of damage are around Jamaica Bay and on the west shore of Staten Island. Higher damage amounts are seen in Manhattan due to higher building values.This is a citywide 1% annual chance flood, but in reality it’s unlikely that a single flood event would impact the entire city.
HAZUS-MH Results for Economic Losses from a 1 Percent Annual Flood Flood in New York City
New York City's open space and natural areas—its parks, trees, beaches, wetlands, and barrier islands—often act as the first line of defense against flooding. They are also among the city's most vulnerable assets to flooding hazards.
The table shows the acres of parkland in New York City that are in the 1 percent annual chance floodplain according to FEMA's 2015 PFIRMs. New York City’s 1 percent annual chance floodplain encompasses more than 6,000 acres of city-owned parkland, which represents about 20 percent of all city-owned parkland.
Parks and Open Space in the 1 Percent Annual Chance Flood Floodplain
|Overall Parkland (Acres)||Parkland within 1 Percent Annual Chance Floodplain (Acres)||Parkland within the 1 Percent Annual Chance Floodplain as a Percentage of Total|
|NYC DPR parks||30,162||6,046||20.04|
Waterfront parkland is notably varied and houses a number of site typologies and features, including but not limited to waterfront esplanades and greenways, beaches and boardwalks, wetlands and natural areas, playgrounds and outdoor fitness areas, recreation centers and other buildings, athletic fields/courts and other outdoor recreation facilities, marinas, floating docks, and piers.
Some city parkland is composed of natural areas that are able to withstand and recover from most storm events without significant repair costs. These areas include wetlands, meadows, and dunes. However, while natural, these features can be severely affected by flooding and returning them to their natural function can be difficult and expensive. Damage can include loss of protective shoreline dunes, loss of stabilizing plant material caused by inundation, and erosion.
New York City parklands also contain recreational amenities and landscaped areas including but not limited to ballfields, recreation centers, pools, plazas, amphitheaters, and bicycle and pedestrian paths. Flooding can cause structural damage to these types of facilities and landscaped areas.
All types of flooding present significant risk to the city's park systems. Coastal flooding can submerge wetlands for prolonged periods of time and cause barrier islands to narrow or split. Wave action and storm surge can flood inland vegetation with salt water, erode the shoreline edge, and damage non-salt tolerant trees and shrubs that can act as a buffer for inland parks and neighborhoods. Coastal flooding and wave action also have the potential to damage or destroy constructed features and recreational park amenities.
The map shows the geographic areas of New York City where parks and open space are at greatest risk of flood damage.
Parks and Open Space in the 1 Percent Annual Chance Floodplain
Inland parks, open space, recreational features, and natural areas are also at risk from heavy rainfall. Intense rain events, which produce several inches of rain within a short time period, can severely damage planted park areas that lack adequate drainage, often resulting in loss of vegetation or porous soils that help slow the release of water and impact on adjacent areas.
The New York Panel on Climate Change projects that climate change will exacerbate flooding hazards in the future. The rise in sea level will cause higher storm surges that could flood larger areas. Low-lying areas of the city that currently experience coastal flooding at astronomical high tides will be increasingly vulnerable to ongoing, regular flooding from daily and monthly high tides. Changes like storm activity may lead to more intense coastal storms and an increase in rainfall events.
Flooding from extreme rainfall, or “inland flooding,” may also be exacerbated as a result of climate change. The annual precipitation in New York City is projected to substantially increase in the next fifty years, and combined with the rise in sea level, will exacerbate inland flooding by exceeding the design capacity of the existing stormwater infrastructure.
Heavy Rainfall and Inland Flooding
According to the New York City Panel on Climate Change, the annual precipitation in New York City is projected to increase by 4 to 11 percent by the 2050s and 5 to 13 percent by the 2080s.
In addition to the increase of precipitation in New York City, high tides made higher by sea-level rise temporarily obstruct the ability of stormwater infrastructure to drain streets as designed and prolong flooding events.
NYC Precipitation Increase Projections
|Baseline (1971–2000)||2020s (2010–2039)||2050s (2040–2069)19||2080s (2070–2099)19||21002|
|Middle Range3||High End21||Middle Range3||High End21||Middle Range3||High End21||Middle Range3||High End21|
|Precipitation and Inland Flooding22||Annual Precipitation||50.1 in.||+1 - 8%||+10%||+4 - 11%||+13%||+5 - 13%||+19%||-1 - +19%||+25%|
|Days per year with rainfall exceeding 2 inches||3 - 4||3 - 4||5||4||5||4 - 5||5||-||-|
Storm Surge with Sea Level Rise
The sea height during coastal storms is above the normal level expected at that time and place based on the tides alone. Over the next several decades in New York City, both the frequency of current 1 percent annual chance floods and the height of these flood events are projected to increase.
Sea Level Rise
The NPCC projects that the mean sea level of waters is projected to increase between 11 and 21 inches by mid-century and between 18 and 39 inches by the 2080s. This magnitude of sea level rise would threaten low-lying communities in New York City with regular and highly disruptive tidal flooding. Flooding as severe as today's 1 percent annual chance storm at the Battery would become up to five times more likely if this magnitude of sea level rise occurs.
NYC Sea Level Rise Projections
|Baseline (2000–2004)||2020s (2020–2029)4||2050s (2050–2059)23||2080s (2080–2089)19||210020|
|Middle Range21||High End21||Middle Range21||High End21||Middle Range21||High End21||Middle Range21||High End21|
|Mean Sea Level Rise (SLR)22||0||+4 - 8 in.||+10 in.||+11 - 21 in.||+30 in.||+18 - 39 in.||+58 in.||+22 - 50 in||+75 in.|
|Coastal Flooding22 (Storm Surge with SLR)||Future 1 Percent Annual Chance Flood||1%||1.1 - 1.4%||1.5%||1.6 - 2.4%||3.6%||2 - 5.4%||12.7%||-||-|
|Flood heights associated with a 1 Percent Annual Chance Floodplain||11.3 ft.||11.6 - 12.0 ft||12.1 ft.||12.2 - 13.1 ft.||13.8 ft.||12.8 - 14.6 ft.||16.1 ft||-||-|
Future Flood Maps
New York City worked with The New York City Panel on Climate Change (NPCC) to develop a series of “future” flood maps to guide local resiliency and mitigation efforts. These forward-looking maps were created by using a simplified bathtub model approach that combined the NPCC's "high end" sea-level-rise projections with FEMA's Flood Insurance Rate Maps (FIRMs).
These future flood maps use high-end projections of sea level rise to illustrate how the 1 percent annual chance floodplain could increase over the next several decades. The accuracy of these flood projections is limited, because they were not developed with advanced coastal modeling. Although these maps are not suitable for evaluating individual-property risks, they are extremely useful for public education about the extent of potential future flood risks.
On October 17, 2016, FEMA announced a successful conclusion to the City’s appeal of FEMA’s 2015 PFIRMs and agreed to begin a new process to revise the City’s flood maps.
At FEMA’s expense, two new flood map products are being developed that will show:
- A scientifically-accurate 1 percent annual chance floodplain and elevations to calculate flood insurance premiums.
- A progressive and climate-smart flood map product that better reflects the impacts of sea level rise and climate change.