Fall foliage at Mount Auburn Cemetery in Cambridge, Mass. The region’s recent dry spell may mean a less impressive autumnal display in New England. Photo via Unsplash/ana_essentiels

Fall

Boston’s Rain-Free Month May Mean Fall Foliage Will Come Early This Year

BU biologist explains how recent long stretch of little to no precipitation is impacting Boston area forests and how this pattern is in line with climate change predictions

Like the reds, yellows, and oranges on a painter’s palette, the trees in New England will soon be a lively, bright backdrop that exemplifies all things autumnal, from pumpkin picking to hayrides to apple cider donuts to a cozy flannel. Around Boston, leaf-peeping is a short but sweet couple of weeks, with peak colors typically lasting from the second or third week of October to early November.

Up until a few days ago, environmental experts were predicting a strong fall, with dazzling foliage fueled by the right temperatures and normal summer rain levels in early August. But as of Wednesday, September 18, Boston had not had any significant rain for over 30 days. It’s the city’s fifth-longest dry period on record, with much of New England, including regions in New Hampshire and Maine, experiencing zero to significantly less than average rainfall over the last month. 

“This was an exceptionally dry period,” says Richard Primack, a Boston University College of Arts & Sciences professor of biology who researches the conditions of Boston area forests, including how a warming climate affects the leafing times of plants and wildflowers, historical conservation records, and how noise pollution from traffic affects ecosystems. Although there are sometimes dry periods in New England, Primack says that the impact of this one is very noticeable in local forests. 

“When I walk through the forests, I can see that most of the leaves of the blueberry and huckleberry bushes have dried out and turned brown. In a normal year, the leaves of these plants would still be green, and later turn to yellow or red as the weather cooled in autumn,” he says. “The leaves of black birch are also showing the effects of the drought, and have mostly lost their green color and have turned yellow. In many places, the forest floor has a yellow carpet of fallen birch leaves. This is pretty unusual for mid-September.”

So, what does a lack of rain mean for fall foliage—and for the health of the forests? 

According to Primack, drought often causes leaves to go through the color-changing process called leaf senescence—when green-producing chlorophyll breaks down, revealing yellow, orange, or red pigments—earlier. This is especially true for trees that live in drier areas, like roadsides, hills, or rocky slopes. But for trees that need wetter environments—like red maples or ash—warm, dry weather might cause a delay in fall color.

This means that, well, peak leaf-peeping might not be as vibrant as initially predicted, since different trees will be changing and dropping their leaves at different times. Even with rain in the forecast, some experts are suggesting leaf peepers get out and start enjoying the fall colors earlier than usual, since some trees may soon start losing their leaves as a result of the dry spell. Unfortunately, this may become a more common occurrence as a result of climate change. 

“Dry periods like this are one of the predicted features of global climate change,” Primack says. In general, a warmer atmosphere holds more moisture, which is why climate change is linked to more rainfall in many places and stronger storms, like quickly intensifying hurricanes. For New England, it’s predicted that climate change will not only increase the average amount of annual precipitation, but also make it more variable, with periods of heavy downpours followed by long stretches of little to no rain. 

“So, while we are getting more average rainfall and snow, it will tend to fall in more concentrated events, most dramatically as intense rainstorms, with occasional weeks or even months without rain,” like this recent period, Primack says. 

Boston is far from alone—shifts in precipitation patterns and extreme temperatures due to human-caused climate change will impact every part of the Earth in one way or another, according to the latest Intergovernmental Panel on Climate Change assessment, threatening and disrupting life as we know it. This change in the leaves is just one small reminder of the shifting climate.