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. Don't over-fertilize or use a fertilization the encourages more top-growth (which means more mowing). Keeping water-hungry weeds out of the lawn.
Aerating your yard regularly helps a lawn develop stronger root systems, and reduces thatch buildup. If you have a thatch problem, aerate 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 falljust don't panic.
If you live in an area that frequently has periods of extended droughts, you might think about replanting your lawn with a native grass. Native grasses (i.e. buffalograss). These native grasses require less water and survive extended periods of drought. If native grasses are not a good option for your area, consider switching to a more drought-tolerant grass species such as tall fescue in cool season areas or bermudagrass in warm season areas.