The storm affected about 117,000 homes in Harris County, including 25,000 that suffered major damage. It inundated many areas that weren’t designated as being in a 100-year floodplain, which meant that homeowners weren’t required to have federally backed flood insurance. An estimated 45 percent of Houston households that flooded during Harvey earned less than $50,000, according to a Kinder Institute analysis. About 15 percent earned more than $150,000.

Thousands of Harvey’s victims are now scrambling for a piece of a $15 billion federal relief package, a pot that must be shared with survivors of other disasters this year. More than 411,418 Harvey victims have applied for assistance from FEMA, which has given out $591 million to cover their short-term needs, from hotel rooms to personal property replacement to home repairs — about $1,400 per applicant.

Long-term assistance, administered by the Department of Housing and Urban Development and distributed by local governments, is aimed at the rebuilding of homes, apartment buildings and small businesses. It’s likely that aid won’t trickle down for months. Or years.

For a sense of what it might expect, Houston can look to New York and New Jersey, where, five years after the massive storm known as Sandy, many low-income flooding victims have yet to move back into their homes, while upscale shore towns have sprouted massive new houses built for wealthy buyers.

“Losing your home or having a slow recovery is likely to exacerbate the problem,” said Shannon Van Zandt, a fellow at the Hazard Reduction and Recovery Center at Texas A&M University. “Often people are living at the margin, hanging on by a thread, barely able to handle their finances, and when disaster comes, that kind of shock sends them over the edge and causes them to go into a downward spiral.”

‘Trying to do what’s best’

Harrison is among those hoping to avoid that spiral. She is 29, a single mother of two girls, one 6 and the other born in June. She lives in Sunnyside, a historically African-American neighborhood in south Houston that has one of the city’s highest rates of poverty, crime and unemployment. Her $450-a-month apartment, in an area she describes as drug-infested, didn’t flood during Harvey, but one night, as she and her baby slept, her bedroom ceiling began to leak from all the rain, drenching them.

Ebony Harrison, a single mother of two, makes daily trips to visit her infant daughter, who fell ill after their apartment was damaged by Hurricane Harvey. David Butow / for NBC News

While she waited for her landlord to fix the leak, her infant daughter developed a cough and was hospitalized with a respiratory infection. Harrison said she was with her baby in the pediatric intensive care unit when the landlord texted her saying she had a week to leave the apartment because it was uninhabitable.

Harrison, who makes $10 an hour as an attendant at an adult day care facility, applied for aid from FEMA, which gave her $205 to buy a new mattress, and the American Red Cross, which turned her down.

Harrison’s boss offered to let her rent a house she owned, a godsend at $500 a month, but it was only a temporary solution. Her daily routine became grueling: up at sunrise, dropping her older daughter off at school, a day of work, picking her daughter up and dropping her off with relatives, then several hours at the hospital with her younger daughter. It left her no time to research other emergency assistance programs.

“I’m just a hardworking parent that’s just trying to do what’s best for my girls, and it seems like there’s always something,” Harrison said during a recent break at work. “If it’s not one thing, there’s another. If I didn’t have anywhere to go within those seven days, where would me and my babies be?”

Finding the vulnerable

Harrison’s lament describes one of the biggest challenges of post-disaster recovery: whether victims can find a place to live during the months it typically takes for insurance claims to be processed or to receive long-term assistance.

But those who need housing aid the most often don’t know what’s available or can’t access it, advocates say. That can mean the difference between stability and freefall.

“If you don’t have a savings account, and don’t get a loan or borrow from family, you’re at the mercy of those grants,” said Michelle Whetten, a Gulf Coast-based vice president at Enterprise Community Partners, a nonprofit that pushes for more affordable housing in places wrecked by natural disasters. “Whereas a family with means can start making those repairs right away.”

Researchers have developed a method to identify people who need help the most after a disaster, using an analysis of census data to create a “social vulnerability index” of how well communities can withstand calamities.

“The utility of this is to say, OK, these are the areas we need to target first as a way to prioritize resources, which eventually will be scarce,” said Susan Cutter, director of the Hazards and Vulnerability Research Institute at the University of South Carolina, who developed the index.

In Houston's case, maps show that Harvey's floodwaters deluged some of the city's most economically vulnerable neighborhoods, and some of its least.