The sunshine, infrequent storms, spectacular sunsets, and clear starry nights attract people to Arizona, but such a climate does not produce much surface water. The arid climate also increases water demand, because most crops and urban landscapes mus t be irrigated. The Sonoran Desert of central and southern Arizona is characterized not only by infrequent precipitation but also by extreme temperature swings averaging 35 degrees F between day and night. Annual precipitation varies from 4 inches near Yuma to over 30 inches on mountaintops. The plateau region north of the Mogollon Rim has a cooler but still arid climate.
Summer storms can produce intense downpours, spectacular lightning and flash floods.
More important from a water supply perspective are the gentler winter storms that blanket the mountains and high country with snow, feeding streams and rivers with snowmelt.