If you can, wet the ground all around the plants, or install some misters.. The evaporation from the wet ground, or misters, will help cool the environment around the tree, and make the air higher in humidity, thus lessening the ability of the air to pull moisture out of the leaves. The worst is to have warm (or hot), dry air and wind. Then you have a convection oven, The moving air will draw the moisture out much quicker. Water late at night, or early in the morning so the plant has time to get fully hydrated before the heat comes. If it is already somewhat depleted when the heat comes, watering will help, but it is then a game of catch-up, rather than keeping-up.