Evapotranspiration Adjustment Factor Project

Study Title:

Evapotranspiration Adjustment Factor Study (2014 - 2016)

Background and Purpose:

California’s population exceeded 39 million by the end of 2015 and is expected to reach 45 million by 2020. This projected increase, coupled with a severe multi-year drought and a statewide water distribution problem, necessitates further conservation of an already limited water supply. Landscape irrigation uses a significant amount of water. Approximately 40-50 percent of household water use is used outdoors to irrigate urban landscapes.

2016 marks the fifth year of a major drought in California State Assembly Bill 1881 resulted in California enacting a law on January 1, 2010 reducing the Evapotranspiration Adjustment Factor (ETAF) from .8 to .7 in new landscapes over 2,500 square feet, mandating enhanced water conserving measures in urban landscapes. In December, 2015 a revised ETAF of 0.55 ETo for new landscapes over 500 square feet replaces the previous 0.7 ETo, necessitating even greater conservation. The 0.55 MAWA represents a 21.4% reduction from 0.70. (It is important to note that in some cases recreational turf and water used to produce food crops will remain exempt.)

The goal of our California Department of Water Resources (DWR) project is to measure water use at 30 large urban landscapes in six climate zones that include a variety of ornamental plants with varying water use rates growing under a wide mixture of plant densities and microclimates.  A further goal is to work with site managers to improve irrigation system distribution uniformity (DU) and overall irrigation efficiency at each site.

Confidentiality of Survey and Interview Data Collected

This study is conducted independently of the Department of Water Resources.  As such, the University of California project team will be responsible for collection and analysis of all data used in this study.  Any information shared either through the survey or in an interview will be considered proprietary to the UC project team and will be kept confidential.  The final report will be contain site locations and will be ANONYMOUS.  Companies, organizations and agencies will NOT be identified.


Evapotranspiration Adjustment Factor Study Report



David W Fujino, Ph.D., California Center for Urban Horticulture, UC Davis

Janet Hartin, UC Cooperative Extension

Loren Oki, Ph.D., UC ANR State Extension Specialist, UC Davis


Karrie Reid, UC Cooperative Extension

Chuck Ingels, UC Cooperative Extension



William Baker, William Baker & Associates, LLC