We obviously can't control extended droughts, but we can minimize the damage they cause if we act before they occur. The biggest factor in why lawns fail during extended dry spells, is that they weren't healthy going into the drought. Therefore, you need to do everything you can to make your lawn as healthy as possible when conditions are good for growing lawns.
Regular fertilization that develops strong roots enables your lawn to better survive the dry days. The emphasis here is on regular fertilization. Avoid over-fertilizing or using a fertilization product that encourages more top-growth (which also means more mowing). Keep water-hungry weeds out of the lawn.
Having your lawn aerating regularly helps a lawn develop a stronger root system and reduces thatch buildup. If you have a thatch problem, have your lawn aerated twice a year for several years (once in the spring and again in the fall). If aerating in the spring, do so before applying a pre-emergence herbicide, typically used to control crabgrass. Thatch buildup reduces the amount of water penetrating the soil and encourages shallow root development.
Increase your mowing height as the temperatures increase. This will conserve soil moisture and strengthen root development.
Remember, just as lawns turn brown from extreme water shortages, they will also return to their natural thick green state when conditions improve, usually in the fall—just don't panic.
