WUCOLS categorized thousands of species of landscape plants in six climate zones by their water use: very low, low, medium, and high. The work relied on the consensus of 36 experts from the public and private sectors, including UC. Since the inception of WUCOLS in 1992, additional species have been added, with major updates in 1994, 1999 and 2014. Currently, WUCOLS includes more than 3,500 plants ; and several teams of UC scientists are engaged in assessing the minimum water requirements of additional landscape species, to add them to the database. The WUCOLS database greatly supplements information from the relatively small number of replicated field studies that have directly measured the water use of individual landscape plant species.AB 2717 further refined landscape water conservation legislation, using recommendations by a task force appointed by the California Urban Water Conservation Council. The final report — Water Smart Landscapes for California: AB 2717 Landscape Task Force Findings, Recommendations, and Actions — was submitted to the Governor and Legislature in December 2005 . It included 43 recommendations regarding best practices to improve water use efficiency in new and existing urban landscapes. The top 12 recommendations are listed in table 2.UCCE’s Laurence Costello and Janet Hartin were appointed to the task force along with 28 members representing CDWR, the California State Water Resources Control Board , the California Bay Delta Authority, the U.S. Bureau of Reclamation and also the landscape, equipment manufacturing, building and construction industries, and urban water suppliers, environmental advocacy and environmental justice groups,mobile vertical farm the League of California Cities and the California State Association of Counties. UCCE’s Lorence Oki, Ali Harivandi and Robert Green served as UC representatives on task force working groups.

A key topic of debate among task force members was whether new landscapes should be required to contain a minimum percentage of drought-resistant plants or if adequate water savings could be realized based on a water budget through a variety of other means. The task force ultimately recommended the more flexible latter approach, leaving plant selection to the property owner. UC task force members and other groups represented on the task force supported exemptions from MWELO’s mandated water budgets for “special landscape areas.” These areas included recreational turf and areas irrigated with recycled water. While synthetic turf is a viable water-saving alternative to natural turf in some instances, it can result in undesirable impacts such as high surface temperatures in inland and desert areas and a greater number of player injuries . Several UC academics and other authors, led by Professor Emeritus Ken Tanji, compiled an extensive review of irrigating landscapes with recycled water in Southern California to reduce reliance on potable water. While irrigating landscape plants with recycled water is viable in many situations, salts tend to occur in higher concentrations in recycled water. Leaching these salts below the root zone to prevent plant damage can increase the net water requirement above 1.0 ETAF, the current MWELO allocation for special landscape areas. UC ANR specialists recently published a white paper in support of increasing the ETAF above 1.0 for areas irrigated with recycled water, to provide enough water for leaching.Many of the recommendations developed by UC and other members of the task force were enacted in this bill. These included requiring selection of plants adapted to specific sites while not prohibiting or requiring specific plant species, encouraging the capture and retention of storm water on-site and the use of recycled water, conducting on-site soil assessment and management to prevent erosion and water runoff, applying mulch around shrub and tree plantings, endorsing education of water users on water conservation practices, and encouraging economic incentives to promote water conservation.

As importantly, the legislation encouraged landscape maintenance practices that lead to long-term water conservation, such as routine irrigation system audits, maintaining functional equipment, and minimizing landscape irrigation over spray and runoff. To that end, classes approved by the U.S. Environmental Protection Agency Water Sense program that increase water use efficiency and decrease water loss are regularly offered by the California Landscape Contractors Association, the Qualified Water Efficient Landscaper program, and Rain Bird. The classes promote the incorporation of water-efficient irrigation practices pertaining to irrigation system design, installation and maintenance, and they often include hands-on demonstrations of irrigation system audits. Attendees gain knowledge of best practices that promote healthy water-conserving landscapes and earn certificates of completion, which may provide career advancement opportunities. The bill also required the California Energy Commission to regulate performance standards and labeling requirements for irrigation equipment to conserve energy and water. Examples of heightened performance standards include requiring matched precipitation rate sprinkler heads and other emission devices; separate valves for tree and turf irrigation whenever possible; and the use of original components for sprinkler repair.Between 2003 and 2015, UC received CDWR funding to conduct two studies to further refine provisions within AB 1881. Both studies involved identifying the relative importance and impact of specific best practices — such as conducting sprinkler equipment performance audits and scheduling irrigations based on climate and plant water needs — that maintain the health, performance and aesthetics of large-scale public and private landscapes under reduced water budgets.

The first study examined major causes of water loss on 30 park, school district, commercial and golf course sites in Los Angeles, Riverside and San Bernardino counties. Results identified that over 70% of applied water was lost, due mainly to leaks, sunken heads, improper head tilt, unmatched sprinklers, broken or worn parts, over spray, deflected spray, and improper pressure and line or head placement. The results validated the importance of including best practices targeting irrigation system installation and maintenance in water conservation legislation recommended by the AB 2717 task force. Results of this UC study were also included in a white paper published by CDWR that stressed the importance of best practices in landscape water conservation. The second CDWR-funded study was conducted by us, the authors of this article, in response to the legislative mandate for a UC study to determine the impact of reducing ETAF from 0.8 to 0.7 on plant health, function and appearance. We monitored these factors and the water use of 30 large landscapes with a wide variety of species, microclimates, densities, irrigation schedules and technologies in six climatic zones throughout the state. Of the 30 sites, 21 performed adequately at 0.7 ETAF after implementing best practices that improved irrigation system functioning and decreased water loss ,hydroponic gutter legitimizing the proposed ETAF reduction, which took effect Jan. 1, 2010. Some of the greatest water savings in our study came from improving distribution uniformity and irrigation efficiency. With those improvements, warm season turfgrasses met the 0.7 ETAF standard without impairment to plant health, plant function or aesthetics. Warm-season turf species are more drought resistant than cool-season species; cool-season species did not meet the 0.7 ETAF standard since they are less drought resistant than warm-season species. All 24 shrub sites used considerably less water than the turf sites, although 10 of them increased water use the second year due to malfunctioning valves and management turnover that led to a lack of continuity in site maintenance. Results suggest that drip-irrigated and mulched areas of plants with a mix of medium, low and very low water needs and small areas of warm-season turf can perform adequately at 0.7 ETAF. The results of this study underscored the importance of the MWELO exemptions for special landscape areas. In the absence of an exemption for recreational turf, the options to meet the 0.7 ETAF include reducing the acreage of cool-season turf species, replacing cool season species with warm-season species or irrigating the landscape with non-potable water. Another goal of the CDWR-funded ETAF study was to expand the number of plants listed in WUCOLS. In addition to CDWR, many organizations supported this effort, including the Association of Professional Landscape Designers, American Society of Irrigation Consultants, American Society of Landscape Architects, California Association of Nurseries and Garden Centers, and the California Landscape Contractors Association. The most recent WUCOLS update, WUCOLS IV , includes the water use classification of an additional 1,500 ornamental plants, bringing the total to 3,546 entries. Analytical user data indicates high usage of WUCOLS. During 2014 there were 7,300 users and over 130,000 page views, which increased to over 25,000 users and 538,000 page views during 2016.

There was a slight decrease in hits in 2017, perhaps due to an easing of the drought-related water restrictions that had been imposed by Governor Brown in 2015. Outreach was a major component of the ETAF study. Between 2013 and 2017, our team reached over 7,000 landscape industry professionals through presentations at workshops, symposia, field days and conferences sponsored by UC and industry organizations such as the California Landscape Contractors Association, Irrigation Association, Western Chapter of the International Society of Arboriculture, California Association of Pest Control Advisers, and water districts. In addition, we authored several new UC ANR publications: Sustainable Landscaping in California , Keeping Plants Alive under Drought or Water Restrictions and Drought Tip: Use of Graywater in Urban Landscapes in California .In both UC studies, irrigation system malfunctions resulted in more water loss than could be saved by selecting drought-resistant landscape species . This underscores the importance of proper selection, installation and maintenance of irrigation equipment. Having a landscape contractor firm provide hands-on training to demonstrate these recommended irrigation management practices to site managers significantly reduced water loss following the training in both UC studies .Beginning in 2014 , Governor Brown declared a state of emergency and signed consecutive executive orders to conserve water during the drought and beyond. On April 1, 2015, he imposed statewide mandatory water reductions due to the continuing drought. Important elements impacting urban landscapes included a mandated 25% statewide reduction in residential and commercial potable water use through Feb. 28, 2016 ; replacing 50 million square feet of turf with drought resistant plants; prohibiting the use of potable water for irrigating turf on public street medians and on new landscapes not irrigated with drip systems; requiring urban water suppliers to enact pricing structures consistent with meeting statewide water restrictions; and requiring urban water suppliers to provide monthly information on water usage, conservation and enforcement permanently. In addition, the 2015 order required CDWR to update MWELO to increase water efficiency in new and existing landscapes by using more efficient irrigation systems, gray water, and storm water capture and by limiting turf. Using newer technologies such as precision irrigation hardware and software and renewable energy–powered desalination were also encouraged. On April 7, 2017, Governor Brown lifted the drought emergency in all counties except four but maintained policies that support a core commitment to long-term water conservation through continued mandates on water use reporting, reducing water loss and decreasing the reliance on potable water for landscape irrigation.While comprehensive results and impacts of public policy legislation aimed at increasing landscape water conservation have not been fully evaluated, recent data shows a decrease in urban water use. Total urban potable water use was 20% less in May 2017 than in May 2013 . The U.S. Geological Survey reported a 17% reduction in urban water use throughout California between 2010 and 2015, driven in part by mandatory water restrictions in 2015 . Perhaps more importantly, per-capita water use has fallen steadily over the past two decades, from 232 gallons per day in 1995 to 178 gallons per day in 2010, in response to long-term efforts at conservation, including reduced amounts of water applied to California landscapes . A blip occurred in 2015 when per-capita water use fell to only 130 gallons per day under mandatory conservation. Input from many organizations and stakeholders impacted landscape water use policy and decreased water loss. While UC did provide policymakers with credible and objective research-based information, implementing MWELO and adjusting MAWA required a collaborative effort by a wide variety of groups and individuals vested in maintaining healthy, functional landscapes that perform acceptably under water reductions.In May 2018, Governor Brown signed two bills consistent with his 2017 Making Water Conservation a California Way of Life proposal. SB 606 focuses on landscape water use and AB 1668 focuses on rural and agricultural water use.