‘Temperatures trigger fall colors A warming climate could be bad for fall foliage in years to come. As fall days grow shorter and temperatures drop, the chlorophyll in a leaf breaks down. That causes the leaf to lose its green color.’ There are even YT videos on it, which are mildly interesting and also alarming.

Trees drop their leaves whenever there is not enough water. This is often in winter, because they can’t absorb ice. But any water shortage will do. If you are often in nature you may see warning signs such as rolling or folding of the leaves in an attempt to preserve water before the trees decide to just get rid of them early.