Leaves changing in August?

[DLK55]

A good chance it's stress. Another marker for that would be somewhat smaller leaves than normal and producing more seeds than usual. The tree gets stressed (Commonly by drought) and goes into survival/reproductive mode by producing many seeds. Sort of the tree's way of saying "I believe my time is near, go forth and propagate little helicopters, ensure I live on."

Unfortunately, most of them around here end up in lawn mower bags.

[§AB]

If there is drought here, the trees keep their leaves. Only in very cold Februaries (equiv. to northern August) do the trees loose their leaves, like they did this Feb, which was amongst the coldest on record.