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New England may see a colorful fall because of our rainy growing season

Boston and the rest of New England could be treated to colorful fall foliage this season. Stan Grossfeld/Globe Staff

It’s that time of the year again when folks start asking about the upcoming foliage season.

While every year is a little bit different, there’s never going to be a year where the leaves don’t change and you’ll always be able to find some nice color. The main differences year to year are because of the amount of precipitation during the growing season, how quickly cool weather arrives, and whether there are any big storms that can take down leaves later in the fall.

Unlike last year when we were experiencing a drought, this year has seen adequate precipitation. This means that the trees are full of leaves and most of them are very healthy. I have noticed bacteria and fungal issues on some maple trees because of this year’s rain, and this could lead to some trees losing their leaves without much color. But this will be the exception.

Leaves change colors in the fall due to a predictable set of processes. – NOAA

Let’s look at a bit of science as to why the leaves change in the first place. The purpose of the leaves is to manufacture food for the plants. Basically, chlorophyll is the green pigment in leaves harvesting light energy. This along with CO2 from the air and water coming up from the roots makes sugars for the plant. There’s that added benefit of oxygen for us as a byproduct.

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In fall, the green chlorophyll becomes less efficient, revealing other pigments that are actually always there and working throughout the growing season. Carotenoids, which lead to orange leaves, and a subset of these called xanthophylls and are yellow, start to show through as the chlorophyll wanes. Additionally, a new pigment called anthocyanins is newly produced as the weather turns colder and the days darken. All of these work together to create our fall palette across the landscape. As a side note, anthocyanins also appear in things like apples, which is why many varieties go from green to red.

The long-range outlook has a strong likelihood of warmer-than-average conditions through the rest of September and actually into November. This would be in keeping with more recent autumns, which have trended warmer. Such warmth would delay the average onset of colors from say 20 years ago by a couple of weeks.

The Northeast is likely to have a warmer-than-average autumn this year. – NOAA

What is predictable is the decreasing sunlight down to the second, unlike the temperatures which are less consistent.

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A warmer fall will slow down the process and move the peak foliage deeper into the season. Conversely, an early cold snap can speed things up. As the climate has changed over the past couple of decades, so too has the average date of what we tend to refer to as peak foliage.

The term peak is very misleading. I prefer to think of the foliage season in terms of which trees are changing. The sugar and red maples will tend to turn early, with the oaks coming on much later. In Southern New England there is always some color by early October lasting into the first week of November. Columbus Day weekend is generally a good one to find pockets of perfect color. Cloudy days are great for photographing the color of the leaves but the sunny ones give us those quintessential fall photos. And maybe as we get deeper into the season an early snowfall can even bring some snowliage to the region!

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