Harris Co., Tex.
New Orleans, La.
Tampa Bay, Fla.
Miami-Dade Co., Fla.
New York, N.Y.

Hurricane Harvey pummeled the Houston area with an unprecedented four feet of rain, making it the most extreme rain event in U.S. history. Cars and houses are underwater, and thousands of people have needed or await rescue.

The event has been called a “500-year flood”— a flood event that has a one-in-500 chance of occurring in any given year in that location. Residents in 500-year flood zones aren’t required to purchase flood insurance, even though there is more than a 5 percent chance, more than one in 20, of a 500-year flood over a 30-year mortgage.

The Federal Emergency Management Agency (FEMA) mandates that people living in the high-risk 100-year flood zone purchase flood insurance. While a 1 percent chance every year sounds unlikely, consider that it equates to roughly a 25 percent chance over a 30-year mortgage. A 500-year flood has roughly a 5 percent chance.

Hundreds of thousands of people live in flood-prone areas like Houston, Miami, New Orleans, Tampa Bay and New York.

Mandatory flood insurance

1% or greater

risk of flood

1% — 0.2%

risk of flood

Voluntary

flood insurance

Minimal risk

Mandatory flood insurance

Voluntary flood insurance

1% or greater

risk of flood

1% — 0.2%

risk of flood

Minimal risk

People:

0

2 million

4m

6m

8m

Harris Co.

(Houston)

Miami-Dade Co.

(Miami)

New Orleans

Tampa Bay

New York City

0

2 million

4m

6m

8m

Most people are not required to purchase insurance, even if there’s a chance of flooding

Mandatory flood insurance

Voluntary flood insurance

1% or greater

risk of flood

1% — 0.2%

risk of flood

Minimal risk

0

2 million

4m

6m

8m

People:

Harris Co.

(Houston)

Miami-Dade Co.

(Miami)

New Orleans

Tampa Bay

New York City

0

2 million

4m

6m

8m

In catastrophic flood events like the one in Houston, areas well beyond the 100-year flood line, or even the 500-year line, can end up under water. (Recent reports claim up to 30 percent of Houston may be flooded due to Harvey.) For those without federal flood insurance, there are few resources to help them rebuild after the floodwaters recede.

Here’s what 500-year floods look like, or could look like, in other cities.

Harris County, Tex. (Houston)

National Flood Insurance Program claims for property in Texas

$12B

Hurricane Ike made landfall over Galveston, Tex. in Sept. 2008.

$8B

$4B

0

1996

2008

2016

National Flood Insurance Program claims for property in Texas

$12B

Hurricane Ike made landfall over Galveston, Tex. in Sept. 2008.

$8B

$4B

0

1996

2000

2004

2008

2012

2016

Almost 13 percent of people live in a 100-year flood zone in Houston and Harris County, but as one of the nation’s most populous counties, that’s more than half a million people. Another half-million residents live in moderate risk areas, the 500-year flood zone, where the likelihood of flooding is between 1 and 0.2 percent each year.

This works out to over a million people in moderate-to-high flood-risk areas in Houston alone. Other cities that have recently weathered hits from hurricanes aren't much better off.

Minimum annual risk of flood

1% or greater – 549,000 residents
0.2% or greater – 560,000 residents

New Orleans, La.

National Flood Insurance Program claims for property in Louisiana

In 2005, Hurricane Katrina became the costliest hurricane ever in the Atlantic

$12B

$8B

$4B

0

1996

2005

2016

National Flood Insurance Program claims for property in Louisiana

In 2005, Hurricane Katrina became the costliest hurricane ever in the Atlantic

$12B

$8B

$4B

0

1996

2000

2004

2008

2012

2016

With much of the city below sea level, New Orleans is particularly vulnerable to flooding. Hurricane Katrina devastated the city in 2005, and remains the most costly and one of the deadliest hurricanes to hit the United States. More than ten years later, the city’s population still hasn’t recovered to pre-Katrina levels.

Nearly 95,000 people live in areas at a high risk of flooding, requiring flood insurance, while another 160,000 live in moderate-risk areas. The rest of New Orleans’s population resides in areas protected from floods by levees, though in the event of a levee failure, as in Katrina, those areas would also become vulnerable.

Minimum annual risk of flood

1% or greater – 94,000 residents
0.2% or greater – 282,000 residents

Miami-Dade County, Fla. (Miami)

National Flood Insurance Program claims for property in Florida

$12B

Four hurricanes hit Florida in 2004. One, Charley, made landfall as a Category 4 storm.

$8B

$4B

0

1996

2004

2016

National Flood Insurance Program claims for property in Florida

$12B

Four hurricanes hit Florida in 2004. One, Charley, made landfall as a Category 4 storm.

$8B

$4B

0

1996

2000

2004

2008

2012

2016

Nearly half of all people in Miami-Dade County live in a high-risk flood zone. While the last major hurricane to make landfall nearby was Hurricane Andrew in 1992, sea-level rise has contributed to higher king tides, or the highest tides, and more frequent coastal flooding.

Some areas of Miami-Dade, like the “Billion Dollar Sandbar” in Biscayne Bay, lie on reclaimed land only a few feet above sea level. A large chunk of the county's western side is uninhabited wetlands outside the county's development zone.

Minimum annual risk of flood

1% or greater – 1,273,000 residents
0.2% or greater – 142,000 residents

Hillsborough and Pinellas Counties, Fla. (Tampa Bay area)

Analysts say the Tampa Bay area, which includes the cities of Tampa and St. Petersburg, is the most vulnerable in the United States to flooding and damage in the event of a major hurricane. A direct hit would likely surpass the cost of Hurricane Katrina, with one Boston firm that analyzes potential catastrophic damage estimating a cost of more than $175 billion to the region. More than 30 percent of residents live in a moderate to high risk flood zone.

Unlike the other areas included, the Tampa Bay region hasn’t experienced a direct hit from a Category 3 or higher hurricane in nearly a century.

Minimum annual risk of flood

1% or greater – 605,000 residents
0.2% or greater – 85,000 residents

New York, N.Y.

National Flood Insurance Program claims for property in New York

$12B

Hurricane Sandy hit coastal New York and New Jersey in 2012

$8B

$4B

0

1996

2016

National Flood Insurance Program claims for property in New York

$12B

Hurricane Sandy hit coastal New York and New Jersey in 2012

$8B

$4B

0

1996

2000

2004

2008

2012

2016

New York City sustained an estimated $4.8 billion in uninsured private losses as a result of Hurricane Sandy in 2012, which caused a storm surge that flooded the subway system and shut down the New York Stock Exchange. Only about 7 percent of the city’s population lives in a flood area that is moderate- to high-risk. But because of New York’s size, that amounts to more than 560,000 people — greater than the number of people living in flood zones in the Tampa Bay region. The places most vulnerable to flooding are along the city’s waterfronts in all five boroughs.

Minimum annual risk of flood

1% or greater – 259,000 residents
0.2% or greater – 303,000 residents

Kim Soffen contributed to this report.

About this story

Data on National Flood Insurance Program claims is from FEMA, accessed through FEMA.gov.

The number of people in each risk area was calculated using census block-level data from the 2010 Census and FEMA National Flood Hazard maps.

A large part of New Orleans, particularly areas around the French Quarter and along the Mississippi River, is designated by FEMA as an area of moderate flood hazard, that is “protected by levees from 100-year flood.”

Share

Most Read

Follow Post Graphics