The Cares Act, which the model does not yet take into account, will spend $2 trillion to prop up the economy. It will send most Americans emergency checks ($1,200 per adult and $500 per child) and add $600 a week to unemployment benefits through July. While much of the money will go to people unlikely to fall into outright poverty, its impact on poverty rates is still expected to be substantial.

“It’s unlikely we’ll see poverty numbers as bad as these” in the Columbia model, said Scott Winship, who as executive director of the Joint Economic Committee of Congress works for Senator Mike Lee, a Utah Republican. “This a baseline for how bad things could get if policy didn’t respond. But it’s certainly the case that there will be a lot of hardship experienced — probably more, if I had to guess, than we saw in the Great Recession.”

The researchers will include the Cares Act in future simulations. Among the outstanding questions is whether or how promptly the aid will reach its intended beneficiaries, with many jobless people currently unable to file claims at overwhelmed government offices. “There are so many unknowns at the moment it would be hard to model precisely,” Mr. Parolin said.

Robert Greenstein, president of the Center on Budget and Policy Priorities, a research group that supports anti-poverty spending, said that the Cares Act would lower poverty in the short run, but that the Columbia model pointed to the long-term peril if the crisis endured. “We need to make sure the key provisions don’t expire as long as unemployment stays elevated,” he said.

The Columbia data does underscore the extent to which the safety net reduces poverty. At the start of the pandemic, the poverty rate would have been 25 percent without programs like food stamps and tax credits. That aid lifted 41 million people from poverty and halved the rate, to 12.4 percent.

The pandemic threatens a sharp reversal of fortune for the neediest Americans, who had benefited from the recent years of strong economic growth. Poverty among children, African-Americans and Latinos had fallen to record lows. Still, poverty — and child poverty in particular — remained higher in the United States than in most rich countries, which generally have stronger safety nets.