October is here, and fall is in full swing — but those warm autumnal colors many residents look forward to could be a little disappointing this year.Leaves will likely transition sooner in some areas. But overall, the fall hues might not be quite as vibrant as some might like.The culprit?The lack of rain.The Chicago region has been in a moderate drought since August and September. That can have consequences for when and how leaves change colors.Trees in fall are stressed as they begin to shut down for the cold winter months, said Christy Rollinson, forest ecologist at the Morton Arboretum. 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 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.At O'Hare Airport, rainfall in August and September was about half the 30-year average. Just 3.92 inches of precipitation was recorded 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.For the most part, though, the fall colors could hit their peak pretty much on schedule — but that “peak” might not be all that dramatic.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.”But Kyle Cotner, founder and owner of the website The Foliage Report, which tracks leaf color changes nationwide, said even with the drought "peak color" may still be colorful."You’ll still have vibrant colors, they just won’t stay at peak as long," he said. Cotner pointed out last year Minnesota and Wisconsin had dry seasons but still had colorful leaves.But is there enough time for nature to reverse the consequences of the drought to guarantee we 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.”