MOLINE, Ill. — We are in the midst of peak leaf-peeping season across the United States, signaling the end of the growing season and a return to a cooler weather pattern ahead of winter. Cathie in Morrison submitted an excellent question regarding the timing of fall colors and whether or not it has a relationship to climate change. She asks, "Is climate change impacting fall color? It seems like trees are turning later than 20+ years ago". Let's dig in!
Yes, autumn is getting longer in the Quad Cities
It should come as no surprise that the autumn season is sticking around much longer than it used to in years past, not just here in the Quad Cities, but also in many other parts of the country.
According to temperature data from here in the Quad Cities, our autumn season has grown by more than a week since the 1970s. This includes the average temperature data for the months of September through November, compared to the climate average from the time period 1991-2020. In fact, look at the graph below and it's easy to see the biggest jump is within the last 25 years.
Not only have we seen an increase in the number of days with temperatures above the average for the season as a whole, but we have also seen an increase in that average temperature of nearly 2.5°. While that may not seem like a big deal, it is when you consider that we are taking a period of three months, not just three days or three weeks. Also, remember that winter is the fastest-warming season in the Quad Cities.
The impact on fall color
Warmer temperatures are strongly linked with later leaf fall and also coincide with later fall color peaks. The time period of the most vibrant color can also be shortened quite significantly.
As warmer temperature patterns shift northward with time, tree species can also shift northward with this pattern. This can also cause earlier leaf color and drop.
Rainfall is a biggie we have been dealing with, especially this year with the ongoing drought. This has led to a couple of weeks delay in peak color being displayed, along with less vibrant color in some spots, too.
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