North Carolina’s two largest urban centers—Charlotte and Raleigh—will grow faster than any other large cities in the U.S. over the next fifteen years, according to a projection from a new United Nations study of world population growth.

The U.N.’s World Urbanization Prospects report looks at growth in urban areas across the world, with projections to 2030. John Chesser, the population analyst at UNC Charlotte’s Urban Institute filtered the data down to the U.S., to cities and their surrounding areas larger than half a million.

“I wasn’t expecting them to come out exactly the way they did,” Chesser says.

Charlotte and Raleigh are the two at the top, each projected to grow 71 percent over the time frame.

Rebecca Tippett, director of UNC Chapel Hill’s Carolina Demography program, lists a number of reasons North Carolina is a hotspot.

“The South is new to getting foreign immigration, so that’s driving up population growth,” Tippett says. “You’re seeing return migration to the South, so that’s the reverse of the great migration of African Americans out of the South during the mid-20th century. The cost of living is a little bit lower. There are economically vibrant areas. The weather’s nice.”

Both Tippett and Chesser point out the economy in both cities is growing stronger, which generally pushes up growth.

The projections also push Charlotte and Raleigh past other Southeast cities, which were similarly sized 50 years ago, such as Richmond, Virginia; Nashville, Tennessee; and Charleston, South Carolina.

“I think you’re seeing emergence of two really significant urban centers in the country,” Chesser says.

Austin, Texas, is third on the pared down list. Chesser calls these “adolescent cities,” places large enough to qualify as top cities, but small enough that a growth spurt still creates a big effect.