Obviously, the hotter it is the more moisture is lost. You can sometimes see that in the behavior of the plant. Many plants show their need for water. Their leaves become dull, drooping or wilted. When that happens, plant growth is delayed.
Irrigation is used by farmers to cool plants during extreme weather.
If the temperature exceeds 90 degrees even a five minute spray will refresh the plants and not waste much water. Your soil type can also effect the retention of water. A mix of part clay and part humus can hold water for more than two weeks without rain. Sandy soils, on the other hand, might need watering every day when it is hot. Of course, that is why many gardeners mulch.