Weather Whys: How do the leaves change in the fall?

Weather Whys

Every year, the leaves change from green to yellows, reds, and oranges in the fall. How and why does this process happen?

It’s all thanks to the chemical compounds found within the leaves. Chlorophyll creates the green color we see through most of the year, and is the most dominant. The orange and yellow hues are in the leaf year-round, but covered up by the green. Chlorophyll fuels the plant by changing the sunlight into food for the plant. As fall approaches, there is less sunlight, and that sparks a change within the plant. It shuts off the creation of energy from sunlight and the chlorophyll is broken down.

As the chlorophyll breaks down, it creates a new compound called anthocyanin. This is the only compound not found in the leaf all year long. This creates the red colors we see in fall leaves.

As the green becomes less dominant, the oranges and yellows begin to show through more. The yellow shade is produced by xanthophyll and the oranges is created by carotene. These colors can sometimes be visible all at once in different shades and variations, depending on climate conditions and the type of tree.

The best time to view these colors depends on your elevation and latitude. In Colorado the high mountains approach their peak around mid-September, the Front Range starts around late September, and the plains in mid-October.

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