Los Angeles county is the riskiest county in the US, according to a new Federal Emergency Management Agency (FEMA) index which considers 18 kinds of natural disasters, from earthquakes, hurricanes and tornadoes to floods, volcanoes and tsunamis.

The National Risk Index spotlights places long known as danger spots, like Los Angeles, but some places highlighted run counter to expectations.

For instance, eastern cities such as New York and Philadelphia rank far higher on the risk for tornadoes than Oklahoma and Kansas, where twisters are part of local lore, while the county with the biggest coastal flooding risk is one in Washington state that is not on the ocean, although its river is tidal.

The index scores how often disasters strike, how many people and how much property are in harm’s way, how vulnerable the population is socially and how well the area is able to recover. That results in a high risk assessment for big cities with both lots of poor people and expensive property, ill-prepared for once-in-a-generation disasters.

The degree of risk isn’t just how often a type of natural disaster strikes a place but how bad the toll would be, said FEMA official Mike Grimm.

Two New York City counties, Philadelphia, St Louis and Hudson county, New Jersey are therefore FEMA’s top five riskiest counties for tornadoes. Oklahoma county, Oklahoma, which has seen more than 120 tornadoes since 1950, including one that killed 36 in 1999, ranks 120th.

A tornado in the top five would be “a low frequency, potentially high-consequence event because there’s a lot of property exposure in that area”, said the University of South Carolina Hazards and Vulnerability Research Institute’s director, Susan Cutter, upon whose work much of the FEMA calculations are based.

“Therefore, a small tornado can create a large dollar loss.”

In New York, people are far less aware of the risk and less prepared, Grimm said, speaking a day before New York saw a tornado watch. Days later, the National Weather Service tweeted that in 2020 several cities, mostly on the east coast, saw more tornadoes than Wichita, Kansas.

Oklahoma is twice as likely to get tornadoes as New York City but the damage potential is much higher in New York because there are 20 times the people and nearly 20 times the property value.

“It’s that risk perception that it won’t happen to me,“ Grimm said. “Just because I haven’t seen it in my lifetime doesn’t mean it won’t happen.”

That sort of denial is especially true regarding flooding, he said, and is the reason only 4% of the US population has federal flood insurance when about a third may need it.

Disaster experts say people have to think about the big disaster that happens only a few times a lifetime at most, but is devastating when it hits: Hurricane Katrina in 2005, Superstorm Sandy in 2012, a 2011 outbreak of tornadoes, the 1906 San Francisco earthquake or a pandemic, as this year.

“We’re bad at taking seriously risks that happen only infrequently,” said David Ropeik, a retired Harvard lecturer and author of How Risky Is It, Really? “We simply don’t fear them as much as we fear things that are more present in our consciousness, more common. That’s practically disastrous with natural disasters.”

FEMA’s new index can “open our eyes to the gaps between what we feel and what is”, Ropeik said.

FEMA’s top 10 riskiest counties, in addition to Los Angeles, are Bronx, New York (Manhattan) and Kings (Brooklyn), Miami, Philadelphia, Dallas, St Louis and Riverside and San Bernardino in California.

Loudoun county, a suburb of Washington DC, has the lowest risk of all. Three other Washington suburbs rank among the lowest risks for larger counties, with suburban Boston, Long Island, suburban Detroit and Pittsburgh.

Some FEMA risk rankings seem obvious. Miami is the highest risk for hurricanes, lightning and river flooding. Hawaii county is top in volcano risk and Honolulu county for tsunamis, Dallas for hail, Philadelphia for heatwaves and Riverside, California for wildfires.

Himanshu Grover at the University of Washington called the FEMA index “a good tool, a good start” but one with flaws, such as seeming to downplay disaster frequency.

Risks are changing because of climate change and the FEMA index does not seem to address that, Ropeik said. FEMA officials said climate change shows up in flooding calculations and will probably be incorporated in future updates.