According to the Maryland DNR website:
How does weather affect autumn color?
"Temperature and moisture are the main influences......
Picture of a tree with leaves changing color.A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular color displays......
The amount of moisture in the soil also affects autumn colors. Like the weather, soil moisture varies greatly from year to year......
A late spring, or a severe summer drought, can delay the onset of fall color by a few weeks. A warm period during fall will also lower the intensity of autumn colors. A warm wet spring, favorable summer weather, and warm sunny fall days with cool nights should produce the most brilliant autumn colors. "
According to another site (NCSU) describing drought effect on foliage (poor),
"adequate" soil moisture is needed to ensure that trees hang onto their leaves long enough for a decent fall.
Sorry I can't find anything more specific.
MR