Evapotranspiration (ET) is the term used to describe the loss of water to the atmosphere by the combined processes of evaporation (from soil and plant surfaces) and transpiration (from plant tissues) and is needed for irrigation scheduling. Vegable retrieves ETo from CIMIS to calculate ETc for plantings/crops. If the CIMIS ETo can not be obtained, the ETr for your zone is used.
Choose the zone that most accurately represents the micro climate at your location.