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Weather Whys – Why do leaves change color in the fall?

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ABILENE, Texas (KTAB/KRBC) – Fall is usually signified by piles of leaves that were green all summer long, now on the ground in shades of brown, yellow, red, and orange. But have you ever wondered why this change in color happens?

Leaves get their green color from chlorophyll, the main component in the process of photosynthesis, which is how trees make their food. In the summer months, chlorophyll dominates the other chemicals that are present in the leaves. But when the seasons begin to change and days get shorter, and temperatures get cooler, this is a signal for the chlorophyll to change from green to colorless.

As it changes to a colorless compound, this allows for other chemicals present in the leaves to take over the color. If you see a yellow or orange colored leaf, this comes from chemical components like xanthophyll or carotene. These are both carotenoids, which are responsible for the color of – you guessed it – carrots.

If red is the primary color, the compound anthocyanin is responsible. Anthocyanin does more than just change the color of the leaf red; this also plays a large role in preparing trees for next spring. It acts as a kind of sunscreen to protect leaves from bright seasonable light. Some research shows that anthocyanin may even ward off pests.

While color changes are not always guaranteed, there is a good “recipe” for vibrant colored leaves in the fall, and it starts in August. You need to have sunny days, as well as temperatures in the evening steadily getting cooler. This allows for the leaves to make sugars that stimulate the leaves to make anthocyanins. Too many clouds, too much rain, and too much heat in August can make for a much duller fall season.

We tend to see more fall colors earlier in the season starting at higher latitudes. These colors then work their way down through the country as we go through the season. But seeing these colors is a lot like real estate, it’s all about location, location, location. It is also highly dependent on timing. If you try and see them too early, everything will still be green. But if you go too late, then you’ll just see a bunch of dead leaves.

As you head further south across the country, there typically isn’t much to “rake home about” in terms of fall foliage. The state of Texas doesn’t see too much change in color in part because we stay so hot throughout the month of August. But that isn’t the only factor in play. Drought is the enemy of a good fall in terms of foliage. Trees need to be in a healthy state, not water stressed, in order to change colors.

This could be a reason why the Big Country won’t see as much fall-like foliage this season. We have seen at least one category of drought in the Big Country since August 10, 2021. With multiple months sitting in a category of drought, this will definitely affect trees changing colors this season.

Drought monitor from August 10, 2021 compared to the latest drought monitor from October 5, 2021

Keep in mind that not all trees lose their leaves at this time of year. In fact, most conifers – pines, spruces, firs, hemlocks, and cedars – are evergreen. It doesn’t matter where in the United States they are located – they won’t change colors or drop many leaves as the seasons change. But if you want to see more colors in your neck of the woods around fall for next year, consider planting some of the following trees:

  • Flowering Dogwood – produces red during the fall months
  • Redbud – produces yellow during the fall months
  • Japanese Maple – produces orange during the fall months

If you would like to take a trip to see some fall foliage or are curious when we’ll see our peak here in the Big Country, you can check out this fall foliage forecast map.

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