After Thursday it appears that we are headed back into a relatively dry pattern. The big question is if this will have an effect on how brilliant the leaves will be this Fall.
Kishwaukee Gorge, Fall 2012
There are a few things that affect the bright, colorful leaves we see during the upcoming season: the weather, of course, but also the pigments found in the leaves. The amount of daylight we receive, believe it or not, has the main impact on the changing leaves.
On September 18th, Rockford sees 12 hours and 26 minutes of daylight. By October 18th, that dwindles to 10 hours and 56 minutes of daylight. As our days grow shorter and nights grow longer, the trees naturally know to slow down and eventually stop their production of chlorophyll.
Chlorophyll is a pigment found in trees that helps photosynthesis to occur. Photosynthesis is the process where plants use the sun’s energy to produce sugars, which nourish the plants. During Fall, the trees begin to store those sugars for the Winter months.
When trees stop producing chlorophyll—the pigment that makes the leaves green—two other pigments take over. Carotenoids and anthocyanins become the dominant pigments in a leaf. Carotenoids give us the oranges, yellows, and browns while anthocyanins give us the bright reds and deep purples we see in October.
Peak Color during a Normal Year
Warm sunny days, cool nights, and near normal rainfall in the weeks just before Autumn are perfect conditions for the most vibrant colors.
Last year’s hot and dry weather kept the trees from producing enough sugars to sustain the pigments that produce the most vivid colors. We saw many leaves turn brown and yellow and fall to the ground quickly.
This year, our rainfall has been below average since July. So the colors will not be as bright as they could be. But, they will be much more colorful than last year! Even with the drier than normal conditions, we are still looking at the middle of October for peak color in northern Illinois and southern Wisconsin.
Get those cameras ready!
Posted under First Look, science, statistics, sunlight, weather
This post was written by Joe Astolfi on September 18, 2013