With October’s arrival and fall in full swing, many people get excited to see tree leaves transition to their warm autumnal colors. But experts say this year may be different.
That’s thanks to the Chicago region being in a moderate drought in August and September. That can have consequences for when and how tree leaves change colors.
Christy Rollinson, forest ecologist at the Morton Arboretum, said trees in fall are stressed as they begin to shut down for the cold winter months. Drought only exacerbates that stress, and thus forces trees to change color early.
“It was kind of questionable at the end of August, but as September evolved we were seeing a kind of pronounced browning and color across the region,” Rollinson said.
Moderate droughts are expected to take place once every five to 10 years, according to Brad Rippey, a U.S. Department of Agriculture meteorologist and author of record for the U.S. Drought Monitor, which declared the moderate drought.
At O’Hare Airport, rainfall in August and September was about half of the 30-year average. It received just 3.92 inches of precipitation over the two months compared with an average of 7.44 inches.
More severe droughts can lead to leaves turning brown and dropping faster. Rippey said that’s happening in Kentucky and Ohio, which are experiencing worse droughts than Chicago.
Rollinson said trees in the Chicago area that have suffered from this dry spell have mostly been in urban environments, where the sun and surfaces absorbing heat combine to accelerate the color-changing process.
Typically, “peak color” — when the leaves are at their most vivid — happens in mid-to-late-October. Jacob Burns, curator for plant collections at the Chicago Botanic Garden, said the peak is likely to fall in that range, but the colors may not be as eye-catching.
“Trees kind of have to have the perfect adequate moisture, and then cool nights, and when you’ve got drought and warm nights you’re not going to get that color shift that everyone desires,” he said. “They’re going to turn yellow or brown and not those vibrant colors.”
Burns said he recently traveled to Wisconsin and noticed trees there were showing signs of drought, too.
Trees in environments or with irrigation systems to keep them moisturized will be the best chance to see the colors this season, Burns said.
Is there enough time to reverse the consequences of the drought and still have vibrant colors this fall?
“The science of fall color is complicated,” Rollinson said. “A lot of it is going to depend on what happens over the next few weeks. If temperatures stay more moderate, and we can get a little bit more precipitation then I think average color is best guess.”