Climate change will lead to wetter US winters, modeling study finds

Most Americans can expect wetter winters in the future due to global warming, according to a new study led by a University of Illinois Chicago scientist. 

Using climate models to investigate how winter precipitation in the United States will change by the end of the 21st century, a team led by Akintomide Akinsanola found overall winter precipitation and extreme weather events will increase across most of the country.  

The study in npj Climate and Atmospheric Science also reported an increased frequency in “very wet” winters — those which would rank in the top 5% of U.S. historical total winter precipitation. By the end of the 21st century, these previously rare winters would happen as often as once every four years in some parts of the country. 

Combined with a shift from snow to rain in many parts of the country, the changes will have dramatic implications for agriculture, water resources, flooding and other climate-sensitive areas, said Akinsanola, assistant professor of earth and environmental sciences at UIC. 

“We found that, unlike summer and other seasons where projected changes in precipitation is highly uncertain, there will be a robust future intensification of winter precipitation,” Akinsanola said. “It will accelerate well past what we have seen in historic data.” 

The team used 19 Earth system models in their study and carried out their analysis over the seven U.S. subregions defined in the National Climate Assessment Report. The study compared projected precipitation at the end of the 21st century (2070-2099) to the present period (1985-2014). 

Across the entire United States, they showed an increase in mean winter precipitation of about 2%-5% per degree of warming by the end of the 21st century. In terms of absolute change, the Northwest and Northeast U.S. saw the largest increases. Six of the seven regions will also experience more frequent very wet winters, with the sharpest increases seen in the Northeast and Midwest. 

The southern Great Plains — states along the southern border such as Texas and Oklahoma — was the only region where projected changes were very small and highly uncertain. In this region, more frequent extreme dry events will offset or outweigh the increasing extreme wet events, Akinsanola said. 

The findings highlight that changes in winter precipitation will have a significant impact nationwide and, in some regions, more impact than expected changes in spring and summer precipitation.  

The mix of precipitation also will likely change in many areas. Previous studies have projected that as temperatures rise, more precipitation will fall as rain rather than snow, resulting in lower snow depth. This reduced snowpack plus higher rain will stress existing systems. 

“There will be a need for updating or upgrading infrastructure, because we’re not just talking about the mean precipitation, we’re also talking about an increase in extreme events,” Akinsanola said. “Drainage systems and buildings will have to be improved to cope with potential floods and storm damage.” 

In current and future work, Akinsanola will use higher-resolution models to predict changes in precipitation, heat waves, compound dry and hot extremes and other extreme events on a more local level. He conducts some of his research in association with the Environmental Science Division at Argonne National Laboratory, where he holds a joint appointment.

Written by Rob Mitchum