During drought years, deep soaking of the root zone with water will help reduce tree stress. In periods of extreme drought, deep watering should occur approximately once a month. The water needs to reach the fine feeder roots which are located approximately 6-12 inches below the soil surface. It is very helpful to apply mulch to the root zone to help keep the water from evaporating.
Your arborist will help you determine an optimum watering schedule and method of application. Usually soaker hose or inline emitter hose is preferred to oscillating sprinklers. This is because water should not spray onto the trunks of trees to help prevent root collar diseases.