City of San Diego Water Department - Landscape Watering Calculator Zip code San Diego County has three distinct climate zones: coastal, central, and inland. All of the zip code areas of the county have been grouped into one of these climate zones. When you type your zip code into the Calculator, it automatically uses a 5-year average of weather conditions in your climate zone. This 5-year average has been collected from specially designed weather stations in your area that estimate the amount of water needed by plants each day.