NEW ORLEANS — The children upended by Hurricane Katrina have no psychological playbook for the youngsters displaced by Harvey, or those in the path of Irma, the hurricane spinning toward Florida.

In the aftermath of Harvey, more than 160 public school districts and 30 charter schools have closed in the sprawling Houston metropolitan area. Families have scrambled to higher ground, some to other cities like Dallas or San Antonio, others into shelters. Thousands of children will have to adjust on the fly, bussed for hours to new schools from makeshift housing. Texas officials are scrambling to coordinate mental health support; the state’s psychology board is issuing temporary licenses for out-of-state therapists.

In a series of interviews here in New Orleans, 12 years after Katrina’s devastating floods, young survivors, now in their early 20s, agreed only that overcoming the mental strain of displacement is like escaping the rising water itself – a matter of finding something to hold onto, one safe place or reliable person, each time you move.

Everything else is up for grabs, including the meaning of home itself. “I was so homesick I moved back here soon as I could, right after graduating high school,” Craig Jones, 22, a freelance graphic designer and musician, said in an interview near Pigeon Town, the working class neighborhood of modest homes, diners and shaded porches where he grew up. “I got here and it was the same place but not the same, if you feel what I’m saying.”

A 5th-grader when Katrina hit, he spent the intervening years on the move, living in hotel rooms, and finally settling in Houston with his family. When he moved back to New Orleans in his late teens, the streets of his childhood had a new mix of people and an undercurrent of menace he couldn’t place. He became anxious; then began having panic attacks, seemingly at random. He was home-sick, as well as homesick.

“I was walking around with my eyes bugged out,” he said. “They wanted to put me on Xanax, but I wanted no part of that.”

Therapists and social scientists have been trying to characterize the effects of all variety of traumas for more than a century. They have found no equations, no way to predict who will be laid low, who will adjust or who will become stronger.

But they do recognize some distinctive effects of hurricanes. Unlike an earthquake or a fire, flooding from a storm like Katrina or Harvey leaves many houses and buildings still physically standing but uninhabitable, simultaneously familiar and strange, like a loved one sinking into dementia. Surveys done in the first seven years after Katrina found that the rate of diagnosable mental health problems in the New Orleans area jumped by 9 percent – a sharper spike than after other natural disasters – and the effects did not discriminate much by race or income.

“Our reading of that is that the stressors were so severe they overwhelmed the coping skills of most kids,” said Kate McLaughlin, director of the Stress and Development Lab at the University of Washington, who led the research team.

Lacey Laurence, now 22, escaped Katrina’s waters on an air mattress, as police officers shoved away bodies with oars, and some proprietors guarded swamping businesses with shotguns. An uncle disappeared, probably drowned. A 12-year-old cousin got lost, alone, and wasn’t heard from for hours. She and her parents landed in a dry area of the city, staying with relatives.

“I was at this new school, my friends were gone, and kids would be saying things – about my old neighborhood, about my family,” Ms. Laurence said. “I was getting into fights; real fights, violent ones. That was something I never did before, ever. But you lose everything and you don’t know how to deal with it – no one prepares you for that.”

She finished school and now teaches young children precisely those skills: how to stay safe; how to manage emotions; how to stay focused on what they can control, and adjust to what they cannot.

In the years after Katrina, a pair of sociologists, Alice Fothergill and Lori Peek, made regular trips to New Orleans, interviewing hundreds of people who had been hit hard and tracking their lives over time, checking in repeatedly. After seven years, the pair identified a rough pattern among displaced children: some had not regained their footing, losing years of schooling and later sinking into unemployment; others adapted, even thrived; and there was a third group, of young people in an uncertain holding pattern, keeping themselves upright but unsteadily, managing lingering effects, like depression or anxiety.

Those in the first group tended to have few resources to start with, and lost them all. “It’s a cumulative vulnerability, in which for instance the family struggled before the storm, then could not get out, and the child lost the fragile supports he or she had,” said Dr. Fothergill, a professor at the University of Vermont.

Dr. Peek, a professor at the University of Colorado, said that those children who adapted fastest typically had family and networks with resources that held together through Katrina, or acquired strong allies along the way: teachers, pastors, shelter workers who fought for help on the child’s behalf.

The third group – “fluctuating equilibrium,” the sociologists called it – usually had lost virtually everything but had one solid anchor: a mother, a father, a teacher, an older sibling.

Dr. Fothergill and Dr. Peek published a book laying out their thinking, “Children of Katrina,” told through the lives of several children.

Five years later, as those children have moved into young adulthood, it’s clear that trajectories are not always smooth lines. Jordan Bridges, 29, evacuated with his mother and siblings ahead of Katrina to a friend’s place near Washington, D.C. His father stayed behind to work. Mr. Bridges’ life in Washington was a fire-shower of emotion.

“My mom was overwhelmed. I had to get my little brother to school every day; it was like every day I woke up and had to forget everything that had happened to day before,” said Mr. Bridges, who now works for a New Orleans social justice nonprofit, and sings in a band, Melomania. “Homework – forget it. Nothing.”

Although “trauma” can mean many things, and is generally considered destructive, its demands can force people to learn what their abilities are and which are most useful when all seems lost. Studies by Roxane Cohen Silver, a psychology professor at the University of California, Irvine, and others have found that adults who report having taken no serious hits – like, say, the death of friend, a serious illness, a natural disaster – generally do not score as highly on measures of well-being as people who have survived traumatic events. It is people who have been through at least two traumas, and less than six, who score highest.

After returning to Louisiana, Mr. Bridges said he got blindsided again, this time in Baton Rouge, where he got a degree in biology from Louisiana State University. He and his brother tried to stop a fight, he said, but they never got the chance. The police arrived and beat them both, he said, and shattered his jaw. He spent months in the hospital with his jaw wired shut.

“I honestly believe that having been through Katrina helped me get through that,” he said. “I don’t know that I would take either of those back, honestly. It’s part of who I am. I became a storyteller. I’m an optimist; going through those things, I know nothing can put my light out.”

This city still bears visible scars of Katrina, buildings that stand empty, crippled monuments to the flooding. But the young men and women interviewed for this story had one thing in common. They all came back.

They returned not home, but to a permutation of it, one with an existential uncertainty that is no abstraction.

“Now I know, I’ll never stay in any big storm,” said Shaysa Shief, 22, who was trapped with her family for days after Katrina, with no power, little food or water. “No one’s going to come help you; you are on your own.”

You look over your shoulder here, they said, literally and mentally. And you watch the weather forecast.