When Connecticut's changing leaves will be most brilliant
Analyzing the spectrum of fall foliage

Climate change could cause Connecticut's leaf-peeping season to come earlier, according to researchers.

The peak time to witness the leaves changing colors depends on what part of the state you live in but generally happens during October.

This year, forestry officials say the best time in the northern part of the state will be the first half of October while the southern half of the state will wait until the second half of month.

However, researchers said there is evidence that this year’s drought has caused some tree species, such as maples, to start changing colors and dropping leaves in September.

Their foliage estimation map is based on the observations and experience of forestry workers at the Connecticut Department of Energy & Environmental Protection.

For science, Trend CT determined the daily dominant color of leaves between 2012 and 2015 by scraping and analyzing thousands of images from the state’s outdoor haze and visibility cameras on Cornwall Mohawk Mountain and Talcott Mountain Science Center in Avon that overlooks Hartford.

Below you can use the slider to compare photos from the same day of four years of data. White spaces represents gaps where photos were not available.

Around Talcott Mountain, the leaves begin to turn orange and yellow in early September and those become the dominant colors in mid October.

Connecticut stands out among the other New England states because it’s where the northern hardwoods meet the central hardwoods, said Chris Donnelly, urban forestry coordinator for the state’s Division of Forestry.

This effectively gives Connecticut two color peaks – one in the first two weeks of October and the second in the second two weeks.

“There’s more diversity in terms of number of trees in Connecticut than in most parts of the country,” said Donnelly. There are nearly 20 different types of trees across Connecticut with different fall color tendencies.

On Mohawk Mountain, some leaves began to turn orange as early as mid-September. Green doesn’t stop being the dominant hue until mid-October.

The chemical chlorophyll in the leaves is what gives them their green color. In the fall, when temperatures cool, trees begin to block the flow of water to their leaves so the chlorophyll breaks down, revealing vibrant yellow, orange or red.

A variety of factors contribute to changing the colors – from temperature to moisture to light exposure. Generally, the more light trees get and the lower the temperature – as long as it’s above freezing – the more brilliant the foliage will be, said officials. A dry year can help the fall colors linger longer than usual.

Autumn phenology, what researchers call the changing of the colors and falling of the leaves, also can be affected by factors such as drought, heat, and rainfall between spring and fall.

Weather change

Donnelly recalled that 2011 was a particularly dull year because of Hurricane Irene and rain storms that followed throughout the season. The leaves dropped prematurely, and a fair amount of fungus prevented the colors from reaching their full potential, he said.

Weather has a powerful impact on fall color, particularly changing weather patterns and climate change, according to research published by Yingying Xie while at the University of Connecticut. Based on climate projections, Connecticut and New England’s color changes will happen over a shorter time and earlier in the year because of more extreme weather patterns in coming decades.

Previously, researchers said the fall colors would change later in the year because of warmer evening temperatures, said Xie, who is now a post-doctoral research associate at SUNY Buffalo. But record-breaking summer heat, heavier rainfall and stronger storms, as well as periods of drought will cause trees to start the nitrogen-preserving process of dropping leaves earlier.

The more trees are stressed, the earlier they shut down for the year.


It’s very difficult to determine in a given year the timing and vibrancy of fall leaf changes, said Donnelly.

While this year’s drought has caused some trees to drop some of their leaves early, that doesn’t necessarily predict the rate at which other leaves on that tree will follow. Some leave fall to give the tree extra water to power through the rest of the season, especially if recent rainfall encourages them to stick around.

“If we get a lot of rain and wind close to the peak, that could put a damper on it,” said Donnelly. “If we get temperatures near to, but above freezing during the last month – the reds may become more pronounced.”

The summer of 2016 was particularly sunny, which can mean more opportunity for photosynthesis if a tree can find adequate moisture.

“The short answer with the drought is that it will likely be at least a factor – but how much of a factor depends upon all of these other things” said Donnelly.

Check our work — The data and analysis for this story are available in Trend CT’s GitHub repository. Read about our philosophy on reproducibility and open data.