我找到不同的说法了。听谁的?
Why do some years have autumns more colorful than others?
The intensity of autumn leaf coloration each year is different. This is because the amount and exposure of colored chemicals in leaves depend on the weather. Green chlorophyll disappears fastest during an autumn with bright sunlight and cold days. This disappearance quickly exposes the leaves' orange and yellow pigments to view.
Dry weather concentrates sugar in the cell sap, which speeds up manufacture of red compounds. So the most colorful autumns depend on the weather.
Dry, sunny days of an Indian summer that are followed by cool, dry nights will create the best season for the fall leaf show. You can predict good viewing if you analyze the weather conditions.