Dr. Laurie Pearce lists off the items she keeps ready in case disaster strikes. There are pouches filled with water, space blankets, flashlights and batteries, a hand-crank radio with a charger for her cellphone, a stash of garbage bags ("They can be used for keeping people warm as well, by cutting holes for the heads," she says), first-aid kits, a spare pair of glasses, food packages, waterproof matches, an extra supply of her husband's medication, hygiene products, tissues and two decks of cards.

And that's only some of the contents of the backpacks she has designated as "grab-and-go" bags, to be used if she and her family ever have to flee. She also keeps a rope, a shovel and two or three blankets in her car. In her house, she has a stockpile of supplies and a generator in case of a power outage. The house itself, situated in the district of North Vancouver, is equipped with a sprinkler system in case of fire, and it's built on granite rock and bolted in to brace for earthquakes and landslides.

Since she's an expert in disaster management, it's Pearce's job to think about the calamitous what-if scenarios that many of us dare not. According to a Statistics Canada report released in 2015, only about half of Canadians have an alternate source of heat for an emergency, and less than half have an alternate source of water. Only 21 per cent reported taking other types of emergency precautions, such as checking and replenishing emergency supplies, keeping an extra supply of fuel, keeping exits clear and making arrangements for their pets in case of emergency.

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"Some people don't know what to do to prepare" for a disaster, says Pearce, an associate faculty member at Victoria's Royal Roads University who teaches in the masters program in disaster and emergency management. But, she adds, "some of it is denial."

When it comes to facing the risks of large-scale disasters, whether it's the threat of nuclear war, a terror attack, a hurricane or raging wildfire, many people have a hard time envisioning – let alone preparing for – worst-case scenarios. News reports last month, for instance, noted that some residents of Guam expressed they were unfazed by the threat of North Korean missiles. "I'm not afraid as many people think we're afraid. Life just goes on and we have trust and confidence in God and our military," Keandra McDonald, a student at Guam University, told Australia's ABC News.

And even as Hurricane Irma edged closer to Florida, some hold-outs dismissed warnings to steer clear of its path. As one woman, Adriana Spitale Del Campo, told The Wall Street Journal, "Worrying beforehand is worthless."

One explanation for why people shrug off disaster is that they may not fully understand the risk, Pearce says. She finds it shocking that many who live around the Cascadia subduction zone on the Pacific coast of North America still do not fully understand their risk of a destructive earthquake.

Others, she suggests, find the prospect of large-scale disaster overwhelming. Seeing the images of entire buildings flattened this month by the magnitude 8.1 earthquake that struck southern Mexico, for instance, may make individuals feel powerless to prepare for a similar event.

"When people see all these awful situations … they think 'Well, what's the point? If this is going to be so devastating, what's the point of me doing anything, really?'" she says.

Such was the response of some Cold War-era undergraduate students at Stanford University, who were asked to estimate the likelihood of nuclear war in a study in the Journal of Applied Social Psychology, published in 1989. As the study author reported, "One respondent wrote, for example, that 'thinking about this just scares me and makes me feel really impotent.'" (The author noted that some respondents even sent their questionnaires back with expletives and hostile remarks, refusing to make an estimate.)

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And it's not like we necessarily lack the imagination or interest in thinking about doom and gloom. We've proven that with our appetites for dystopian movies about zombies, plagues and Armageddon, New Yorker journalist Kathryn Schulz writes in her Pulitzer Prize-winning feature on the likelihood of a large-scale Cascadia earthquake. "Where we stumble is in conjuring up grim futures in a way that helps to avert them."

In some cases, people feel powerless or resigned to do nothing because they lack the resources to prepare for a disaster. For instance, Pearce says, urban apartment dwellers may not have the physical space to keep emergency stockpiles, and those living in poverty don't likely have the financial means to purchase items for "grab-and-go" bags.

The opinions and behaviours of others also influence how people respond to emergency situations, Pearce says, pointing to research on the evacuation of the World Trade Center in New York on Sept. 11, 2001, which revealed that workers were concerned about leaving without the approval of their bosses. Many delayed vacating the buildings to attend to last-minute tasks, such as gathering their personal items, making phone calls or shutting down their computers, according to a study published by the U.S. Centres for Disease Control and Prevention. They appeared not to grasp the urgency of their situation.

"Some of those decisions cost people their lives," Pearce says, explaining that people also tend not to decide whether to vacate on their own.

In the context of a hurricane, she says, "It might be, 'Oh, the neighbours aren't home yet, maybe we'll talk to them.' Or maybe, 'Aunt Suzy's over here, and I'll wait for her to get back,' or 'My mom isn't here yet.' So people want to make a decision as a group, and then if some people can't join a group, they'll wait for that person, for example."

Research has also shown that people can underestimate the danger they face and be overconfident in their ability to overcome it, says Dr. Etsuko Yasui, associate professor of applied disaster and emergency studies at Brandon University.

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Yasui explains researchers have found people make decisions based on their previous experiences. That means if you've experienced a hurricane and emerged unscathed, you'll probably approach the next one in the same manner. Similarly, one might expect that if you've never lived through Cold War-era nuclear attack drills, you may be less alarmed by the exchange of threats between the United States and North Korea than those who have.

"If [people] cannot make an accurate understanding of the scale of the event, it is difficult for them to imagine the impacts of the event," Yasui wrote in an e-mail.

In their chapter of Risk Conundrums: Solving Unsolvable Problems, published earlier this year, authors Howard Kunreuther, Paul Slovic and Kimberly Olson point out this kind of "availability bias" can make people underestimate the likelihood of a disaster before it occurs, and overestimate it afterward. Such thinking helps explain why people often buy insurance right after a disaster, but then cancel their policies after they've had several loss-free years. It's difficult to convince them that they should celebrate not having suffered any loss and still maintain insurance coverage, the authors wrote.

But then, what may seem irrational to others "can be perfectly rational for the individuals because they have their own rationale for doing it," Yasui says. In other words, everyone interprets risk differently.

The problem for disaster-management experts is there are a multitude of factors that influence how each individual perceives risk, and how he or she behaves, says Dr. Ali Asgary, associate professor of disaster and emergency management at York University. He notes experts from a wide range of disciplines, from psychologists to geologists, have spent decades trying to tease them out.

Some of these factors involve the hazard itself, for example one's physical proximity to a hurricane or earthquake zone, while others can be considered informational factors, such as the type of media coverage available. There are also a host of personal factors, including age, education and gender, Asgary says, noting that in some situations, women have been found to be more cautious than men, particularly when they have children.

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Socioeconomic or contextual factors, which include the level of an individual's trust in institutions, also play a role in how they perceive and react to risk, he says.

"If I believe that my government is 100-per-cent ready, is there to take action and help me … then I would relax and say, 'Don't worry,'" Asgary says, whereas others who have little faith in their government are more likely take measures to protect themselves.

Recognizing the involvement of all these factors means there's no one-size-fits-all approach to encouraging the public to prepare for a disaster, he says. Warnings and preparedness efforts would be more effective if they were targeted to specific groups, based on the way they perceive risk. Moreover, he adds, people are more likely to heed warnings and take action if they are encouraged to participate in the disaster-management planning process, such as engaging in emergency exercises or workshops to voice their opinions.

But as much as people should be thinking about and preparing for worst-case scenarios, scaring them can be counterproductive, Asgary says. When warnings are too negative, "people actually feel helpless or feel it's something beyond their control," he says, whereas when people are told they can take specific steps to reduce their losses from a worst-case scenario to a less-terrible scenario, they're more inclined to feel empowered.

In general, he says, when people feel like, "'yes, actually, we can actually do something to reduce the risk…' then they will react to this [information] positively."