There is little doubt that summers are getting warmer--areas with sufficient rainfall in the past may receive inadequate supplies now. Demands for water seem to be increasing with rising populations, so that while we cope with climate change we must also manage the problem of equitably allocating available resources. Dr. Jeffrey Sachs, one of the architects of the Millennium Development Goals of the United Nations, said in a March 2009 interview at Columbia University's State of the Planet Conference, "No one will take water for granted in the future." However, people have survived dry conditions from time immemorial, so there is reason to be optimistic that with effort, your garden can survive drought too.
Evaluate your garden for wasteful sprinklers that throw water into the air where much of it evaporates, or leaky hoses that lose water before reaching plants. Get rid of those and replace them with water saving drip irrigation systems or soaker hoses that put water directly where it is needed, when it is needed.
Replace thirsty plants with species requiring less water--native plants from arid climates are particularly good choices. Mediterranean culinary herbs like rosemary, oregano, and thyme are excellent as they are adapted to arid conditions and make wonderful additions to the larder. Okra, sunflowers, many bean varieties, amaranth, mustard greens, New Zealand spinach, purslane, native (heirloom) corn varieties from the southwest, sweet potatoes, peanuts, eggplant, Swiss chard and even a few melon varieties all do well in hot dry conditions.
Eliminate patches of bare soil open to the heat of the sun--cover with mulch or plant drought tolerant living mulches to shade soil and retain moisture. Herbs such as prostrate rosemary, roman chamomile or sweet woodruff are good choices. For paths where foot traffic is heavy, use ground cooling flagstones interspersed with creeping thyme.
Introduce shade to the garden--plants need a certain amount of sunlight per day, (some as much as eight hours) but more than six hours of sun are generally not necessary for most plants, and definitely unhealthy for water retention during droughts. Block sunlight with shade cloths, taller plants or even just propped squares of cardboard on south or west facing sides to reduce the impact of hot afternoon sun. If a more permanent solution is necessary, build a fence on that side.
Save water from other than the tap sources, for recycling in the garden--collecting rain in rain barrels is an obvious choice, but you can also filter (through a sieve or window screen) water from dishes, baths and even laundry (provided it does not contain chlorine bleach or harsh detergents). Collect in buckets and use to spot water when the whole garden does not need to irrigation.
Use containers to garden as much as possible--though they will require more frequent watering, they ultimately use less water since it is not soaked up by surrounding soil. Containers can also be moved into the shade when they become too hot.