One of the joys of fall is the beautiful fall foliage—the reds, oranges, yellows, and browns. How will weather affect their color? Is it a good year for pretty leaves?
How Does Sunlight Affect Autumn Leaves?
Surprisingly, it is not the weather that is the primary factor that determines when the leaves turn. It’s the amount of sunlight. Leaves manufacture chlorophyll, which stores the energy of the sun. It’s chlorophyll that gives leaves their green color.
When the days grow shorter during fall, less chlorophyll is created. The green fades, and the colors of other leaf chemicals become visible. It’s amazing how pretty these chemicals can be. Anthocyanins make the leaves look red and purple, xanthophyll colors them yellow, and orange leaves contain carotenoids. It’s a rainbow of chemicals.
Weather determines how vivid the fall foliage will be and how long it will last.
How Does the Weather Affect Autumn Leaves?
If the weather is cold enough, it can end the chlorophyll production early. This is why the high mountains in Colorado have an early leaf season. Cold also makes colors more intense.
At the same time, warm weather can increase production a bit, allowing the green to last longer. In the 120 years of US weather records, temperatures have grown warmer, especially in cities, and the leaves now turn a couple of weeks later than they did a century ago. The US east of the Great Plains and most of the Rockies have been warm.
Temperature departures (°C) over the last 30 days. Source: NOAA/CPC
Dry conditions are rough on trees and actually can end chlorophyll production early, especially for trees that turn red. They may turn red early, but the stress also makes the trees shed their leaves sooner. Dry areas have shorter color seasons.
45% of the continental US is dry.
Fall Foliage Predictions 2016
While the Great Plains and Midwest have had good rains, the East and West have been dry.
Bottom-line, thanks to the weather, the leaf season may be short this year. This could be an especially short season for leaf peepers in New England and the Southern Appalachians.
Get out and enjoy them while you can, and let us know how the leaves look in your area!