With climate change causing more extreme weather across the state — intense rainstorms, floods, droughts and powerful derechos — Iowans have never needed trees more, experts say.

That need comes as the state continues to recover from losing 7 million trees when a 2020 derecho swept across Iowa — an event the National Weather Service termed the most damaging thunderstorm in U.S. history. And the impacts of climate change are expected to become more severe in the decades ahead without action to lower greenhouse gas emissions.

An annual state climate assessment, endorsed by about 200 university scientists, researchers and faculty at Iowa higher education institutions, said trees can help offset severe weather tied to a warming planet. "But trees are not going to solve the problem," Heather Sander, a University of Iowa associate professor of geographical and sustainability sciences, said in an online news conference Wednesday.

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"Our trees store and take up significant amounts of carbon, helping us to offset some of our carbon emissions," Sander said. "However, the magnitude of these emissions is so great that this benefit of trees in offsetting carbon emissions is relatively small.

"The greatest benefits of Iowa's trees in addressing climate change will come in helping us to handle the extreme heat and weather that we will face in the years ahead," she said.

Trees cool the air by releasing water vapor from their leaves and shading the land beneath them. They also absorb "huge volumes of water" during intense rainstorms, Sander said, reducing flooding. And "their roots hold soil in place, keeping it from washing away," she said.

Their benefits will be needed in so-called urban "heat islands" that could grow in size and intensity. By 2050, Des Moines is expected to see 35 days with temperatures over 95 degrees Fahrenheit, up from the current four, according to Jerry Schnoor, co-director of the UI's Center for Global and Regional Environmental Research. That number will grow to 95 days by 2080, he said.

Climate change threatens the trees themselves, however.

"By midcentury, that's 2041 to 2061, five to 15 days per year will exceed 106 degrees," Schnoor said. "Such heat waves will create a huge problem for trees in Iowa."

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At the same time as Iowa faces extreme weather challenges — including a historic derecho in December 2021 that spawned 61 tornadoes — the state is struggling to replace about 7.2 million trees lost in the 2020 derecho, which swept through the middle third of Iowa.

Iowa cities lost about 4.5 million trees, or 13%, of the state's 34 million urban trees, according to a 2021 Iowa Department of Natural Resources report. The state's rural lands lost 2.7 million trees, and the storm damaged an estimated 32,773 acres of urban tree canopy.

State Sen. Joe Bolkcom, an Iowa City Democrat who participated in the news conference, said the Legislature appropriated $500,000 to help cities and towns replant the lost trees.

The state money, however, "doesn't come close to meeting the state needs," said Shannon Ramsey, CEO at Trees Forever, a nonprofit group that helps communities, volunteers and civic organizations plant trees and bushes.

The cost to replace the lost trees in especially hard-hit Cedar Rapids is estimated at $37 million over a decade, she said. Des Moines and Davenport also suffered some of the largest tree losses in the storm, with winds that surged up to 140 mph in some counties. It damaged thousands of homes, business and vehicles, along with millions of acres of cropland.

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Linn County, which includes Cedar Rapids, lost 953,224 trees, the DNR report says. The city of 132,000 people previously said it lost 669,000 mature trees, roughly 70% of its urban canopy. Polk County and Des Moines lost 642,348 trees, and Scott County and Davenport lost 514,163 trees, the state report estimated.

Even when the trees are replaced, it will take years for them to provide many of the benefits that the lost mature trees did, said Jan Thompson, an Iowa State University professor of natural resource ecology and management.

“In the face of climate change we should both plant more trees and provide essential care for the precious trees we already have,” Sander said.

Donnelle Eller covers agriculture, the environment and energy for the Register. Reach her at deller@registermedia.com or 515-284-8457.