Historical ET is the estimated ET for an average year. In California's Central Valley, ET does not vary greatly from year to year, especially when ET is collected across a number of days.
Historical ET tables for mature:
Immature Trees do not use as much water as mature orchards, so the ET information must be adapted.
For more information on using Historical ET for irrigation scheduling, see the following:
"Scheduling Irrigations: When and How Much"- ANR Pub 3396
Click here to download a free copy of the complete document:
"Reducing Runoff from Irrigated Lands: Understanding Your Orchard's Water . . ."- ANR Pub 8212