Water your trees during a dry spell!
The best time is at night. The best method is to use a soaker hose so the water gets absorbed directly into the soil. Buy 100 feet or more of soaker hose for large trees. Make a spiral of circles around the tree spaced three feet apart on each go-round. Turn on the hose and watch the water come out to make sure it is dripping off the hose, not spraying into the air. Be sure to let the water run long enough so it penetrates deeply into the soil, which might take several hours. Trees should get about an inch of water a week. You can use a pie pan set under the hose to monitor how much water is getting to the roots.
You can also prepare for a dry spell by mulching your trees to help maintain moisture.