WISCONSIN — Thousands of U.S. cities, including some in Wisconsin, are in danger of becoming ghost towns by 2100 due to a multitude of issues, ranging from the decline of industry to lower birth rates to the impacts of climate change, according to a study published recently in the journal Nature Cities.

These and other factors could cause further erosion in the populations of about 15,000 cities nationwide — in every state but Hawaii and the District of Columbia — making them virtual ghost towns with only a fraction of the population they previously had, according to the study.

Overall, the researchers from the University of Illinois Chicago found that population projections for 2100 suggest that nearly half of 30,000 cities nationwide could experience population losses of between 12 percent to 23 percent, and in 27 percent to 44 percent of the populated area.

In Wisconsin, the study said areas around Milwaukee, Green Bay, Wausau, and Superior could all see massive population drops.

But the Madison area will likely see increases.

Depopulation creates enormous, unprecedented challenges for planners, including possible disruptions in basic services like transit, clean water, electricity and internet access, the authors wrote.

Urban planning now is based on growth, but nearly half of U.S. cities are depopulating, senior author Sybil Derrible, an urban engineer at the University of Illinois Chicago, told Scientific American.

“The takeaway is that we need to shift away from growth-based planning, which is going to require an enormous cultural shift in the planning and engineering of cities,” Derrible said.

The authors said the exit from cities for the suburbs creates additional strain and possibly limits “access to much-needed resources in depopulating areas, further exacerbating their challenges.”

Also, they added, immigration could play a vital role in reversing the trend, but also that “resource distribution challenges will persist unless a paradigm shift happens away from growth-based planning alone.”

The Northeast and Midwest are the most likely regions to see big population losses, with Vermont and West Virginia the hardest hit, with 80 percent of cities between the two states expected to shrink.

Five states — Illinois, Kansas, Michigan, Mississippi and New Hampshire — could see population declines in about three-fourths of their cities, according to the study.

Around 40 percent of cities are growing, including New York City, Chicago, Phoenix and Houston. Most of the places projected to see population growth by 2100 are located in the South and West, according to the study.

Most previous studies were based on big cities like Chicago, New York and Los Angeles, “but that doesn’t give us an estimation of the scale of the problem,” lead study author Uttara Sutradhar, a doctoral candidate in civil engineering at the University of Illinois Chicago, told the Scientific American.

The study was based on U.S. Census data from 2000 to 2020, data from the Census Bureau’s American Community Survey and five future climate scenarios, called the Shared Socioeconomic Pathways. That model shows different ways demographics, society and economics could change by 2100, depending on how much global warming the world experiences, according to Scientific American