- Author: Joanna Solins
Front yard with water-wise landscaping. Photo Credit: Cadenasso Lab, UC Davis
California's urban water agencies have long relied on conservation measures to promote reliability and manage costs. Since landscapes are a large portion of water demand in California cities, many water agencies encourage water conservation by incentivizing the replacement of water-intensive turf lawns with water-efficient or “water-wise” landscaping.
In California's Mediterranean climate, traditional turfgrass lawns require irrigation to maintain their appearance through the hot summer months. Inefficient, poorly managed spray irrigation systems can also result in considerable water loss from runoff and evaporation. Replacing turf and overhead sprinklers with low-water-use plants, alternative ground covers like mulch and kurapia, and more efficient drip irrigation systems can potentially save hundreds of gallons of water per square meter every year.
Although the water savings from turf replacement can be substantial, generating widespread buy-in is a challenge. Landscape renovation can be expensive and intimidating, requiring residents to learn new landscape management practices or pay for professional assistance. In addition, many people appreciate their lawns as spaces for children, pets, or entertainment. Some prefer the look of turfgrass, especially where neighborhood norms promote a unified lawn aesthetic.
To help overcome cost barriers and encourage water-wise landscaping, government agencies and water suppliers commonly offer “cash for grass” programs, in which residents are offered a rebate for landscaping expenses based on the amount of turf they replace. These programs also aim to promote neighborhood adoption of water-wise landscaping by providing attractive examples. Turf replacement incentive programs are likely to expand under proposed new water use efficiency regulations, Making Conservation a California Way of Life (AB1668 - SB606).
While large-scale, regional turf replacement programs in Southern California have been evaluated in peer-reviewed studies, questions remain about the extent and impact of these programs in other parts of the state. How widely are turf replacement programs utilized, and by whom? Are these programs responsible for a substantial amount of water-wise landscaping?
Water-wise landscaping in Sacramento
With these questions in mind, we wanted to understand how both rebate recipients and houses with independently installed water-wise landscaping were distributed across an entire city in inland Northern California. The study was recently published in the Journal of Urban Ecology.
We visually surveyed the front yards of all single-family homes in 100 census tracts across the city of Sacramento—109,062 homes in total—and compared the prevalence of water-wise landscaping with the city's turf replacement rebate data. We especially wanted to understand how this landscape water conservation measure was being adopted by communities of varying socioeconomic and demographic characteristics, and which communities were benefitting from the rebate program.
Front yard with traditional turf. Photo Credit: Cadenasso Lab, UC Davis
In Sacramento, the City's Department of Utilities has offered a rebate of (typically) $1.50 per square foot of turf removed since the summer of 2014. To qualify for the rebate, replacement landscapes must meet several criteria, including efficient irrigation systems and approved plants that cover more than half of the area at maturity. The planting requirement addresses an important concern with turf replacement—the potential for an increase in urban heat. Lawns have a cooling effect through evapotranspiration, and if they are replaced primarily with non-living groundcovers, temperatures could increase. However, such program requirements can make some residents reluctant to participate.
When we conducted our visual survey of front yards in 2018, we found that approximately 10% of Sacramento's single-family-homes had water-wise yards, while 88% had conventional lawns. Only around 3% of water-wise yards were rebate recipients, though, meaning that the vast majority—97%—of water-wise yards were landscaped independently from the city's rebate program. We also found support for neighborhood adoption effects, with clustering of water-wise yards at the city block scale.
The prevalence of independent water-wise yards should be good news for water conservation, since it would not be feasible for the city to fund many thousands of turf replacement projects. However, independent turf replacement projects don't need to comply with the city's requirements for plant coverage or irrigation system efficiency, meaning that they could be contributing to increased urban temperatures or failing to save water.
Our study also showed that water-wise landscaping was more common in census tracts with less diverse, more highly educated, and more affluent populations, as well as fewer households with children. Rebate recipients followed the same trends, suggesting that rebates weren't overcoming barriers to adoption. The uneven distribution of resources necessary for turf replacement—money, time, and information—is likely an important driver of this pattern, along with cultural or functional preferences for lawns. Lawns may play a particularly important role for families as spaces for children to play.
Photo Credit: Cadenasso Lab, UC Davis
A Tool in the Toolbox
Turf replacement is one important tool in the water conservation toolbox, and our research suggests that many residents voluntarily install water-wise landscapes even without a rebate. However, adoption is not equal across communities. The roots of this disparity likely reflect uneven distributions of resources and preferences.
With thoughtful program design and outreach, incentive programs could help overcome some of these barriers, although funding and staffing limitations in water agencies pose a challenge for implementation. For instance, carefully crafted direct installation programs could reach lower-income residents who find it difficult to pay up-front costs associated with rebates. Tailoring efforts to the needs of lower-income and marginalized communities will be important to ensure that they do not end up with unirrigated, high-heat landscapes instead of attractive, water-wise yards.
In the Sacramento region, focus groups conducted for the Regional Water Authority revealed that some residents have a very strong preference for lawns. In these cases, water suppliers may have greater impact by promoting efficient irrigation practices, turfgrass varieties that use less water, and climate-appropriate shade trees. Partial lawn conversions are also a viable water-saving strategy, and one that Sacramento's rebate program supports.
As California's cities grapple with climate change, water reliability, cost effectiveness, and meeting new water use efficiency standards, reducing high-water-use turf lawns will continue to be an important adaptation strategy. Figuring out how to support effective and equitable landscape water conservation programs must be a focus of future research and evaluation studies to promote a California where everyone benefits from climate adaptation measures.
Joanna Solins is an Environmental Horticulture Advisor with UC Cooperative Extension, serving Sacramento, Solano, and Yolo Counties, and is an Affiliate Researcher with the California Institute for Water Resources and the UC Davis Department of Plant Sciences.
Acknowledgments: Many thanks to Erik Porse, Amy Talbot, Jasmin Green, and Mary Cadenasso for their input and assistance with this post.
Additional Reading
Green, J. C., Solins, J. P., Brissette, L. E. G., Benning, T. L., Gould, K., Bell, E. M., & Cadenasso, M. L. (2024). Patterns of water-wise residential landscaping in a drought-prone city. Journal of Urban Ecology, 10(1), juae003. https://doi.org/10.1093/jue/juae003
Alliance for Water Efficiency. (2019). Landscape transformation: Assessment of water utility programs and market readiness evaluation. https://www.allianceforwaterefficiency.org/impact/our-work/landscape-transformation-assessment-water-utility-programs-and-market-readiness
Matlock, M., Whipple, R., & Shaw, R. (2019). Just for the turf of it: Turf replacement as a water conservation tool. Journal of Soil and Water Conservation, 74(5), 449–455. https://doi.org/10.2489/jswc.74.5.449
Pincetl, S., Gillespie, T. W., Pataki, D. E., Porse, E., Jia, S., Kidera, E., Nobles, N., Rodriguez, J., & Choi, D. (2019). Evaluating the effects of turf-replacement programs in Los Angeles. Landscape and Urban Planning, 185, 210–221. https://doi.org/10.1016/j.landurbplan.2019.01.011
Simpson, S.-A., Altschuld, C., Ortiz, A., & Aravena, M. (2023). Green to gold mile: An environmental justice analysis of drought and mitigation policy impacts on home landscapes in Sacramento California. Landscape and Urban Planning, 234, 104729. https://doi.org/10.1016/j.landurbplan.2023.104729
- Author: Jeffrey P. Mitchell
CASI's Mitchell helps with KVPR interview on climate change
January 16, 2022
CASI's very own Jeff Mitchell, along with UC ANR colleagues Mae Culumber, George Zhuang, Karl Lund, and Bob Hutmacher, helped with information on their research that is related to climate change in an interview with KVPR reporter, Kerry Klein, at the UC West Side field station on January 14th 2022. The segment was part of the Valley Report on KVPR and was titled, “Climate change resilience begins with water say these UC ag researchers.” An audio recording and a copy of the report written by Klein are available at https://www.kvpr.org/environment/2022-01-14/climate-change-resilience-begins-with-water-say-these-uc-ag-researchers
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- Author: Jeffrey P. Mitchell
December 28, 2021
KMJ580's Don York, who produces the daily “Ag Report” on the Fresno-based radio station, interviewed Alyssa DeVincentis and Jeff Mitchell about work they and a larger team of researchers at UC Davis conducted on water-related impacts of winter cover crops throughout the Central Valley. The interview aired at 5:05 AM on York's Tuesday, December 28th, broadcast and can be heard by clicking on the link here below.
The work that DeVincentis and Mitchell summarized with York involved ten almond orchard and tomato field sites in which side-by-side comparisons of soil water content during the winter cover cropping period from November through March were conducted from 2017 through 2019. The study sites spanned San Joaquin Valley sites in Arvin, Shafter, Five Points, and Merced, as well as Sacramento Valley locations in Davis, Durham, Orland, and Chico. Basic conclusions stemming from the work include the finding that cover crops grown in the winter growing window do not lose more soil water than fallow bare ground despite considerable dogma about the likelihood that they deplete soil water reserves during the winter growing period.
This finding adds important information that may help local Groundwater Sustainability Agencies (GSAs) create groundwater management plans that are required for compliance with SGMA, the Sustainable Groundwater Management Act. If remote-sensed imagery is used to determine a farm's overall water use, winter cover crop vegetation may appear on satellite images as a net water loss, while in actuality, because cover crops perform other functions such as improving soil water infiltration from rain, increasing soil aggregation and water holding capacity, and reducing the energy available at the soil surface by providing shade by the cover crop canopy, the net effect tends to be no additional water loss relative to a bare soil surface during the winter period.
The team that worked together on this research included then UC Davis PhD student, DeVincentis, her major professor, Samuel Sandoval-Solis, Daniele Zaccaria, Anna Gomes, then an undergraduate student at Davis and now a PhD student at Stanford University, and CASI's Mitchell.
The project is summarized in a manuscript that will be published in an upcoming issue of UC's quarterly peer-reviewed journal, California Agriculture, in 2022. A pdf copy of the research article is also available below.
- Author: Jeffrey P Mitchell
July 7, 2020
“Generating and preserving surface residues on the soil – despite being one of the core principles of just about all of the soil health movements and government programs these days – has had very little play in most agricultural fields in California now for nearly ninety years.” That stark assertion come from experienced Cropping Systems Extension Specialist and leader of the State's Conservation Agriculture Center, Jeff Mitchell, who's been in the trenches tinkering with systems that couple residue-preserving and reduced disturbance practices for nearly 30 years.
“The body of research knowledge and experiences on the values of high residue systems is enormous,” Mitchell says, “ and yet most folks in California have not come around to them.” Scientific theory supports the role of residues in reducing soil water evaporation and weed emergence, cooling the soil, and increasing soil carbon gain. “And this theoretical underpinning is now guiding our expanded work with high residue systems to better understand the value they may have in improving biodiversity as well as the efficiency of the carbon, nitrogen and water cycles in California's food production systems,” says Mitchell about the new work that is now underway at several farm study sites throughout the State.
Most annual crop fields that you'll drive by in California typically have close to zero residue on them. “Residues are pretty much managed to make them disappear,” Mitchell observes. Yet, several studies from both irrigated and rainfed regions around the US and including our own work in Five Points have shown that when no-tillage is coupled with high residues, annual irrigation savings can be as much as 4 to 5 inches. In several areas including the Central Great Plains of the US, no-till, high residue practices have positively affected agricultural management and local farm economies with both the intensification and diversification of cropping systems. “What we're doing at this point is trying to figure out just how these residue practices might actually work in various California production systems and minimizing risks associated with transitioning to them.”
More information on these types of systems will be shared on July 23rd as part of the Desert Southwest Soil Health Webinar (https://www.eventbrite.com/e/desert-southwest-soil-health-webinar-tickets-107732693386), slated for July 23rd from 8 AM through 6 PM.
Accompanying photo caption
High residue, no-tillage and cover cropped surface soil conditions achieved in 21-year conservation agriculture research study in Five Points, CA showing the extent of residue cover that can be achieved when these practices are coupled together.
- Author: Ben Faber
Here's a pretty technical report of water efficiency in avocado - the amount of water it takes to make fruit. It looks like there might be some varieties that could produce more fruit with less water. It's a promising start to selecting a tree that could produce under the increasing drought conditions found in avocado growing areas.
Evaluation of leaf carbon isotopes and functional traits in avocado reveals water-use efficient cultivars
Plant water-use efficiency (WUE) describes the ratio of carbon gain to water loss during photosynthesis. It has been shown that WUE varies among crop genotypes, and crops with high WUE can increase agricultural production in the face of finite water supply. We used measures of leaf carbon isotopic composition to compare WUE among 24 cultivars of Persea americana Mill (avocado) to determine genotypic variability in WUE, identify potentially efficient cultivars, and to better understand how breeding for yield and fruit quality has affected WUE. To validate carbon isotope measurements, we also measured leaf photosynthetic gas exchange of water and carbon, and leaf and stem functional traits of cultivars with the highest and lowest carbon isotope composition to quantify actual WUE ranges during photosynthesis. Our results indicate large variation in WUE among cultivars and coordination among functional traits that structure trade-offs in water loss and carbon gain. Identifying cultivars of subtropical tree crops that are efficient in terms of water use is critical for maintaining a high level of food production under limited water supply. Plant functional traits, including carbon isotopes, appear to be an effective tool for identifying species or genotypes with particular carbon and water economies in managed ecosystems.
Read the article:
https://www.sciencedirect.com/science/article/pii/S0167880918301828