The quick answer is that the sun stays up less during autumn. The leaves need the sunlight for photosynthesis and the trees use the sunlight plus water and carbon dioxide to produce sugars and then chlorophyll. Chlorophyll is green but when sunlight decreases during autumn, chlorophyll breaks down and other pigments take over. Colors like yellows, reds, magentas, oranges and golds appear in the leaves of the trees.
The amount of rain in a year also affects autumn leaf color. A severe drought can delay the arrival of fall colors by a few weeks. A warm, wet period during fall will lower the intensity, or brightness, of autumn colors. A severe frost will kill the leaves, turning them brown and causing them to drop early. The best autumn colors come when there’s been:
- a warm, wet spring
- a summer that’s not too hot or dry, and
- a fall with plenty of warm sunny days and cool nights.