Do your leaves hang low? Do they wobble to and fro? Do they fall to the ground? Do they end up in a mound?
A number of tree species drop their leaves in response to heat stress. Particularly when the weather makes a sudden change to really hot temperatures, trees are not able to pump water up to their leaves fast enough to replace moisture losses. This can be true even when there is adequate moisture in the ground!! Poplars and maples are particularly prone to leaf drop. But if the conditions are right, other species such as birch and ash may drop leaves as well. Fortunately, temporary leaf drop due to hot weather does not usually affect the long-term health of the plant. Make sure soil moisture is adequate. Mulch the root zone to help keep it cool. Prune trees every three to five years to maintain a healthy balanced crown. Then, head in for the air conditioning.