Again, I can say with confidence that the water drops themselves aren't focusing light energy effectively enough to create a 'burn'. After that it's a guessing game I suppose. I assume a lot of maples in your neck of the woods get wind/sunburned by this time of year, with the characteristic browning to the edges of the leaves. The more established a given tree is, whether it is in a pot or planted in the ground, the less it will be effected, as its ability to transpire effectively at higher temps will be greater. Off the top of my head, things that affect transpiration include root mass/health along with soil water content, the overall health of the tree, ambient heat and humidity, exposure to direct sun and wind...I'm sure there are many more. Some of these things may have a role in the browning of those leaves. It might not even be just related to the heat, meaning insects, fungus or viruses maybe playing a role, as well (don't worry, I'm just playing devils advocate now, though it is something to consider). Anyway, when I see leaves like that, the first thing I think of is wind/sun burn which can be exacerbated by root zone issues. Maybe some of the folks living in your neck of the woods and south of you with experience growing maples/tridents might be able to chime in with their experiences. Good luck with the heat,
Dave
I just reread your post. You say the trees most affected are near your house. I thought of two things to consider. Wind may actually be periodically(depending on the prevailing direction of the wind) more intense in the area immediately around the house then further away from the structure. Secondly, your house/deck may actually be reflecting heat onto those trees, particularly if they are on the south/west side of the house.