It’s well known that in a drought, trees near the tops of hills are more likely to die than trees farther down the hill. This is because water runs downhill, and whatever water is captured in the dry conditions is more likely to be stored in valleys. The water table also drops more steeply in higher areas when a drought is underway. Last spring scientists from the USDA Forest Service published some research on two forest plots in the Coweeta National Forest and how they responded to dry conditions in a recent drought. You can read about it at https://www.srs.fs.usda.gov/compass/2017/05/25/topography-and-drought/ and find a link to the original research paper.
