Extreme Weather: 5 Most Vulnerable US Cities

With Hurricane Earl striking the U.S. coast, Heidi Cullen assesses the 5 cities in the country most vulnerable to extreme weather and climate change. Is your home city on the list?

A couple walk along the beach in the rain and high winds as Hurricane Earl moves up the eastern coast on Friday, Sept. 3, 2010 in Virginia Beach, Va. (Evan Vucci / AP Photo)

Heidi Cullen assesses the 5 cities in the country most vulnerable to extreme weather and climate change. Is your home city on the list?

As Hurricane Earl bears down on the Eastern Seaboard, we’re reminded that it’s not just Florida and the Gulf Coast that are vulnerable to tropical storms. Cities up and down the East Coast could suffer tremendous damage from Earl or a similar storm—damage that could be minimized with the appropriate local risk-reduction strategies and infrastructure upgrades before it’s too late.

Back in the 1980s, scientists warned of the critical need for New Orleans to invest in infrastructure upgrades to protect itself against hurricanes. With shrinking marshlands, coastal erosion, and aging levees, the city was incredibly vulnerable to catastrophic hurricane damage. Yet the warnings went unheeded, and what scientists predicted came to pass with Hurricane Katrina. Since then, New Orleans and the federal government have spent billions of dollars to build a fortress around the city—a ring of 350 miles of linked levees, flood walls, gates, and pumps that should withstand the one in a 100-year flood. It sounds impressive—but by comparison, it’s actually quite middle of the road. In the Netherlands, much of which is near or below sea level, law requires that river defenses be adequate for flooding so severe that it has a 1-in-1,250 chance of occurring.

While the new levee system in New Orleans is an improvement, it does little to deal with an important underlying problem: The frequency and intensity of extreme weather events are expected to increase as a result of global warming in coming years. According to Greg Holland at the National Center for Atmospheric Research in Boulder, Colorado, climate models show the potential for a 50 to 100 percent increase in the occurrence of major hurricanes (Category 3, 4 and 5 storms) in the Atlantic in a warming world—the total number of storms in the Atlantic each year may decline.

So as the planet warms, the kind of flood that now has a 1-in-100 chance of occurring will actually happen more frequently. New Orleans has spent virtually nothing to address these compounding effects of climate change, and many scientists see the rebuilding effort as a missed opportunity that will almost certainly result in more losses down the road.

As we look back on this the five-year anniversary of Hurricane Katrina and ahead to the threat from Hurricane Earl, it’s important to identify other cities and regions across the United States that are vulnerable to extreme weather. The list below is drawn from scientists around the country and includes places that because of either outdated infrastructure or increasing geographic exposure are now considered to be the new New Orleans in terms of weather and climate-related risk. This time though, many cities are paying attention to the warnings and taking protective measures.


With 15 miles of stunning beaches, the hip Art Deco architecture of South Beach, more than 9 million tourists a year who collectively spend $15 billion—not to mention the gorgeous solitude of the Everglades—Miami is a city that has a lot to lose.

With most of Miami at about six feet above sea level, and a water table that sits precariously close to the surface, Miami-Dade County is extraordinarily vulnerable to a sea-level rise—it is expected to creep up at least 18 inches by 2050. Intruding salt water could spoil the Everglades and the Biscayne Aquifer that sits beneath it, the principal source of freshwater for South Florida. This threat is compounded when you factor in the risk of more-intense hurricanes, drought, and new diseases—all of which are possible offshoots of climate change. A recent Tufts University study estimates that Florida stands to suffer losses topping $300 billion by the end of the century if it doesn’t adapt to climate change. Miami-Dade, though, is taking steps to protect itself, looking at lessons learned from emergency preparedness and applying them to climate adaptation through an initiative called GreenPrint.

Other cities facing similar risks: Charleston, SC; Tampa, FL; Savannah, GA

New York City

New York is an old city with a new problem. The city’s first subway line opened in 1904, its energy grid was started in the 1880s, and two of its water tunnels were completed before 1936. The new problem is a warming climate. That means more extreme heat, sea-level rise, and more extreme storms, all of which pose significant threats to the city’s antique infrastructure.

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As for the storms, the World Bank Climate Resilient Cities report says that what’s now a 100-year flood could come once every 19 years by the 2050s. Then there’s the threat of a major hurricane. The return period for a Category 3 hurricane, which has sustained winds of 111 to 130 miles per hour, is roughly once in 70 years for New York (it’s about once in 10 for Miami). According to a 1995 study by the U.S. Army Corps of Engineers, a Category 3 hurricane in New York could create a storm surge of up to 16 feet at La Guardia Airport, 21 feet at the Lincoln Tunnel entrance, 24 feet at the Brooklyn-Battery Tunnel, and 25 feet at John F. Kennedy International Airport. The effects could be even greater if the storm hit at high tide. The Army Corps estimates that as many as 3 million people would need to be evacuated.

Like Miami, though, New York is taking steps to adapt. The New York City Panel on Climate Change is lining up strategies to increase the city’s ability to withstand the effects of climate change.

Other cities facing similar risks: Atlantic City, NJ; Boston.

Central Valley California: The Sacramento-San Joaquin Delta

The Sacramento-San Joaquin Delta of California—where the Sacramento and San Joaquin Rivers converge into a mix of canals, levees, and islands, streambeds, marshes, and peat islands—has far more in common with New Orleans than Hollywood. With more than 100 large dams that produce the majority of California’s hydropower, the Delta also provides drinking water for two out of three Californians.

Scientists say the canals and levees have become increasingly vulnerable to a catastrophic failure, whether it arrives abruptly in the form of an earthquake or slowly as the result of sea-level rise caused by global warming. The overarching fear is something called “The Big Gulp.” The name itself pretty much sums it up. If the levees break because of either a severe storm, sea-level rise, or an earthquake, saltwater from San Francisco Bay will come rushing into the delta with devastating speed. If the Delta goes, it can take a lot down with it. In addition to flooding large areas of agricultural land, it would cripple the delivery of water to cities like San Francisco, San Diego, and Los Angeles. Taken all together, scientists estimate that a catastrophic failure of key levees would cost somewhere between $8 billion and $15 billion and proposed alternate visions for the future of the Delta which will be voted on later this year.

Places affected: San Francisco, San Diego, Los Angeles, and Silicon Valley.

Fairbanks, AK

Over the past 50 years, Alaska has warmed more than twice as fast as the rest of the United States. The state’s average temperature has increased 3.4°F and winters have warmed by a whopping 6.3°F. Warmer days and nights are causing earlier spring snowmelt, reduced sea ice, widespread glacier retreat, and permafrost thawing. Permafrost, or permanently frozen ground, underlies about 85 percent of Alaska and when it thaws, it often causes the soil to sink thereby damaging whatever is built on it. Economists estimate that thawing permafrost could add between $3.6 billion and $6.1 billion (10 to 20 percent) to future costs for publicly owned infrastructure by 2030 and between $5.6 billion and $7.6 billion (10 to 12 percent) by 2080 leaving cities like Fairbanks at risk.

Complicating matters is the fact that Fairbanks is no stranger to wildfires. Massive fires during the summers of 2004 and 2005 forced many of the city’s residents to wear surgical masks. By the end of this century, the area burned in Alaska is projected to triple under even a moderate greenhouse-gas emissions scenario. Bark beetles are also on the rise. In the 1990s, Alaska saw the largest outbreak of spruce beetles in the world as rising temperatures allowed the beetle to thrive and drought-stressed trees were unable to fight back. Wildfires and spruce beetle infestations, coupled with growing risk of stronger coastal storms and the potential for impacts of warmer water on Alaska’s fisheries—which include salmon, crab, halibut, and herring—suggest that even cold places have a lot to lose from global warming. That said, an adaptation advisory group has been formed to look at these impacts.

Other places facing similar risks: Anchorage, AK; Barrow, AK, the Kenai Peninsula, AK

Las Vegas

Straddling the border between Nevada and Arizona, the massive walls of the Hoover Dam were built to tame the flow of the magnificently wild Colorado River, which stretches more than 1,450 miles from Colorado's Rocky Mountains to the Gulf of California. It is the Colorado that ultimately fueled the growth of cities like Las Vegas, providing roughly 30 million people in the West with drinking and irrigation water.

Today, Las Vegas is more vulnerable to water shortages than almost any metropolitan area in the U.S., though Phoenix and Albuquerque are not far behind. The U.S. West has seen explosive population growth since 1970. Couple that growth with significant increases in temperature and a drier Colorado River system and you have the making of a large-scale Western water crisis. A recent study suggests a one-in-two chance that all of the Colorado River’s massive reservoirs, including Lake Mead and Lake Powell, could be fully depleted by 2050 if current management practices continue. Add in the risk of more wildfires and a growing bark-beetle infestation and climate scientists see the makings of a crisis on several fronts. In the meantime, the Western Water Assessment is looking at both climate impacts and adaptation strategies.

Other cities facing similar risks: Phoenix; Albuquerque, NM

Heidi Cullen is the author of The Weather of the Future. She is a senior research scientist with Climate Central, a nonprofit research organization through which she reports on climate change for news outlets, including PBS NewsHour, Time.com, and The Weather Channel. She is a visiting lecturer at Princeton University, a member of the American Meteorological Society, and an associate editor of the journal Weather, Climate, and Society.