Mayor Muriel E. Bowser (D) addresses a community meeting at Friendship Baptist Church in Ward 6 on Feb. 11 in Washington, where a discussion was held about replacing the D.C. General shelter with family housing facilities. (Amanda Voisard/For The Washington Post)

The number of homeless families in the District has soared by more than 30 percent compared with a year ago, according to a federal estimate released Wednesday.

For the first time since the annual census began in 2001, homeless children and their parents in the District outnumbered homeless single adults, a population beset by mental illness and disabilities that historically has loomed as the larger and more in­trac­table problem in cities nationwide.

On one day in late January, officials counted 4,667 homeless children and their parents, compared with 3,683 single adults.

It is impossible to know precisely what is driving the increase. But city officials and advocates for the poor agree that rising costs in one of the country’s hottest real estate markets, combined with a policy of helping families without a permanent place to call home, has produced record numbers at city shelters.

“We are in the midst of a very serious affordable-housing crisis,” said Kate Coventry, an analyst at the left-leaning D.C. Fiscal Policy Institute.

[Real estate decisions could imperil Bowser’s new shelter plan]

The District, New York City and Massachusetts are the only major U.S. jurisdictions that guarantee homeless residents a right to shelter. All three are grappling with a substantial increase in the homeless population.

In Washington, the surge in family homelessness began in 2010, amid an economic downturn that coincided with increased real-estate speculation that drove up prices in many working-class neighborhoods. The latest jump can be traced in part to Mayor Muriel E. Bowser’s fulfillment of a campaign pledge to make it easier for vulnerable women and children to receive city services. Her administration dropped a requirement that families must wait until freezing nights to receive open-ended placements in city shelters or overflow motel rooms.

Bowser (D) has proposed spending about $173 million on homeless-related services this year — an increase of about $13 million over last year and more than the combined budgets for libraries, parks and the University of the District of Columbia.

Advocates call the move to year-round access a major improvement. Under Bowser’s predecessor, Vincent C. Gray, restrictive city policies kept many homeless people from getting services and tamped down the numbers in the shelters, said Amber Harding, of the Washington Legal Clinic for the Homeless. “The increase reflects the fact that this administration is actually funding and serving families who are in crisis.”

[Gray’s record on homelessness examined]

But the spike in demand has been so dramatic that even advocates have begun to question parts of the mayor’s approach and whether Bowser can control a problem that by many measures is only getting worse.

The rise in homeless families is tied to a string of social and government failures, observers say. Some of the homeless are foster children who did not successfully transition to adulthood through District programs. Many are young women who became pregnant as teens. Others dropped out of troubled D.C. public schools and have few job skills.

But Bowser’s administration blames housing affordability, saying soaring rents have pushed the poor to the streets.

The mayor has proposed building and leasing new shelter sites for 280 families, which would cost almost $660 million over 30 years. She says the facilities will enable the city to more quickly transition families to permanent housing and jobs.

But the shelters would house just 25 percent of families now in city care, according to the latest homeless count. And although the city would be able to close its dilapidated megashelter at the former D.C. General Hospital, most homeless families would still be warehoused at roadside motels in the city and in Maryland.

[Homeless D.C. families spend blizzard in suburban motel rooms]

Advocates also warn that the new data shows the mayor is falling behind on her pledge to largely end homelessness by the end of 2018. They say the mayor has shortchanged her promise to subsidize permanent housing for the most troubled singles and families by more than $20 million next year and has earmarked far too few slots for affordable housing units for homeless families — about 100, or less than 10 percent of the population now in shelters.

“It’s worrying that there is not a greater investment,” Coventry said.

Laura Green Zeilinger, who oversees the city’s homeless services, warned last year that the homeless census could look worse this year before it gets better. She and Bowser chose to expand access to shelters before implementing new programs to keep the population from growing. That meant 464 families entered shelters before winter, and about the same number as last year — 1,000 — sought shelter during hypothermic nights.

Zeilinger said the administration was determined to meet the needs of the city’s most vulnerable residents even though it would mean a higher tally in the annual census, administered by the U.S. Department of Housing and Urban Development.

“We were able to help families earlier, and because of that, we know that we are providing better services and support than in previous years, and that’s important,” Zeilinger said.

The annual count of the homeless is a snapshot taken in cities nationwide on the same night, often by volunteers scouring under bridges, in woods and elsewhere. In the District, it took place as the city dug out from a massive snowfall in late January. Rather than conduct a physical search, officials counted the number of families in shelters.

The tally doesn’t fully capture the scope of the city’s homeless problem.

Any family that enters a shelter is entitled to stay until it is offered city-subsidized housing afterward, typically for longer than a year. More than 1,100 families are living in such apartments, An additional 1,250 formerly homeless families and more than 4,700 formerly homeless single residents hold permanent housing vouchers because the city has determined that they are unlikely to be able to support themselves.

A spike in vouchers in the city, including over 750 for homeless veterans and paid for mostly by the federal government, helped cut the number of homeless individuals by nearly 4 percent.

Advocates say that if Bowser and the D.C. Council are serious about ending family homelessness, funding must increase significantly, likely across the $200 million threshold — about the amount the city spends annually to run its Fire and Emergency Medical Services department.

“You can’t just say that you have a goal to end homelessness — you have to do something dramatic and huge to accomplish that,” Harding said.