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The irrational way people calculate hurricane risks

Hurricane Wilma, which hit Florida in 2005, was strong — but Irma could be much worse
Hurricane Wilma, which hit Florida in 2005, was strong — but Irma could be much worse
Stan Honda/Getty Images

It may seem obvious that whether people decide to evacuate a hurricane zone depends on their perceptions of how severe storms in the region tend to be.

Unfortunately, our research suggests that people’s judgment about how the intensity of storms has changed over time is less than rational. It has less to do with an objective evaluation of trends than with their memory of the last hurricane that they lived through.

This could be bad news for Florida residents, because the last hurricanes to make landfall there, in 2005, Wilma and Dennis, had wind speeds of 105 miles per hour. Hurricane Irma could potentially have much higher winds, though the storm remains in flux as of mid-day Saturday.

If residents are relying on memories of Wilma and Dennis to shape their decisions, they may fail to take the steps necessary to protect themselves.

Quizzing people about hurricane intensity

For our study, published last year, we examined data from the 2012 Gulf Coast Climate Change Survey, which asked 3,850 people in coastal counties whether hurricanes that hit their community had been getting stronger, were less strong, or were about as strong as in the past. We compared their answers with the actual storm histories.

We also looked at how people’s answers related to their survey answers to other questions regarding such things as political affiliation or attitudes toward climate change. These tend to overlap, of course, since many Republicans do not believe in climate change.

We found that maximum wind speed associated with the last hurricane to make landfall in their county was the most powerful predictor of how coastal residents perceive changes in hurricane strength along the Gulf Coast. People who experienced higher maximum wind speeds in the last hurricane they experienced are more likely to think hurricanes are becoming stronger.

Psychologists have a name for this tendency: the “availability heuristic.” The most “available” information about a hurricane is immediate past experience, and so that comes to dominate more analytical approaches to interpreting storm patterns.

The survey respondents were asked to describe general trends, but we think it’s safe to say that people’s opinions about storm trends are likely to shape people’s response to the next storm they face — in this case Irma.

In addition to people whose most recent experience was with a relatively weak hurricane, Republicans and climate-change deniers also tended to be doubt that future storms would be stronger than those in the past.

Overrating wind, underrating flooding

There are different ways to evaluate hurricane strength, including wind speed and resulting flooding. We found that wind speed of the immediate past storms tended to shape perceptions of hurricane strength far more than flooding idd — although, as Hurricane Harvey just demonstrated, low-speed, high-rain hurricanes can be at least as dangerous as storms with high wind velocity.

Hurricanes bring triple threats: damaging wind speed, high storm surge, and heavy rainfall. The media’s overemphasis on the Saffir-Simpson Scale (Category 1, 2, 3, etc.), which considers only wind speed, may both create and reinforce people’s tendency to downplay surge and rainfall.

Since risk perceptions have a powerful effect on risk reduction and mitigation decisions, we also investigated how risk perceptions impacted Gulf Coast residents’ support for two long-term adaptation policies: providing incentives for relocation, and funding for educating residents about emergency planning and evacuation.

We found that when people had experienced severe weather conditions in the recent past, such as high wind speeds and storm surges, their support for adaptation policies grew alongside their perception of risk.

The findings suggest that Hurricane Harvey, which left Houston and the surrounding area devastated, may end up making educational and planning programs more political feasible, at least in that city. The Texas Gulf Coast had not seen a storm that powerful since 1961’s Hurricane Carla, which may have led to complacency.

This complacency manifested itself not only in a lack of preparation for strong storms but also in the tolerance for urban sprawl without adequate consideration of environmental risks, such as poor flood drainage. (Houston prided itself on its lack of zoning.) With memories of Harvey fresh in their minds, Houstonians may be more open to plans to protect the city against storm surge, to improve its ability to drain floodwater, and generally to make the city more sustainable.

It is a challenge for disaster planners — a genuine paradox — that people become receptive to planning for awful events mainly after an awful event. Our research into this topic remains preliminary, so it’s unclear how much of an influence media coverage of Harvey will have on Floridians’ perceptions of risk.

Our study suggests that local experience is the strongest shaper of such perceptions. But let’s hope that, as they pondered evacuation this weekend, Floridians thought fearfully of Harvey’s effects, rather than the milder storms that have hit Florida in recent years.

If that’s what happened, the availability bias could have some positive impacts on disaster preparation.

Wanyun Shao is assistant professor of geography at Auburn University. Siyuan Xian is a PhD candidate in civil and environmental engineering at Princeton University. This article draws on a piece, by the same authors, for The Conversation.

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