Professor Daniele Zaccaria Applying Science-Based Solutions to Growing Water Concerns in the Central Valley

At the University of California, Davis (UC Davis), and the University of California Cooperative Extension, researchers help growers adopt advanced water management solutions in the face of recurring drought and dwindling water supplies. In this interview, Irrigation Leader speaks with Daniele Zaccaria, an associate professor at UC Davis and an agricultural water management specialist at the University of California Cooperative Extension, about how his work helps growers, state agencies, and regulators.

Irrigation Leader: Please tell us about your background and how you came to be in your current position.

Daniele Zaccaria: I’m an irrigation engineer by training. I completed a PhD in civil and environmental engineering at Utah State University in the irrigation engineering division. Before that, I got an MS degree in land and water resources management for irrigated agriculture at the International Center for Mediterranean Agronomic Studies in Italy, focusing on engineering aspects of the performance of largescale pressurized water delivery systems. The distinctive feature of my background is that I have worked for a long time in irrigated agricultural production under limited and impaired water supplies in semiarid climatic conditions, and I have collaborated with professionals from a variety of fields, including hydrologists, civil engineers, agronomists, horticulturists, soil physicists, and crop physiologists. For the last 9 years, I have been at UC Davis’s department of land, air, and water resources, where I have been conducting applied research, extension education, and outreach activities on agricultural water management and irrigation.

Irrigation Leader: Please describe the geographical and hydrological characteristics of the Central Valley, particularly as they affect irrigated agriculture.

Daniele Zaccaria: Geographically, it’s a pretty large agricultural production area with a range of environmental conditions for growing a wide variety of high-value crops and is characterized by various hydrological setups that result in multiple water-related challenges, including water quantity and water quality issues. The scale and intensity of agricultural production in the valley is distinctive. I’ve seen a similar setup in the Central Valley of Chile, but the competition for water among the environmental, agricultural, and municipal sectors in the Central Valley of California is particularly intense and contentious. The heterogeneity of water use challenges and problems across California’s Central Valley is distinctive, as is the variability of water supplies and sources (surface water, groundwater, and treated wastewater).

Irrigation Leader: Please tell us about the University of California Division of Agriculture and Natural Resources (UC ANR) and the UC Cooperative Extension.

Daniele Zaccaria: The UC Cooperative Extension is the executive arm of the UC ANR. We engage with the community and the agricultural production industry to provide science-based solutions to their problems. We have about 700 academic researchers in 40 departments at 4 campuses, about 130 campus-based Cooperative Extension specialists, and 200 locally based Cooperative Extension farm advisors and specialists. We have nine research and extension centers throughout the state of California and 57 local county offices, where farm advisors and specialists provide support to the agricultural production industry and local communities. We tend to work from the bottom up to anticipate problems and to try to address them before they become too serious or complex.

Daniele Zaccaria installing an energy flux station to measure grapevine evapotranspiration in a vineyard at the UC Oakville Experimental Station in the Napa Valley.

Irrigation Leader: How do you engage with farmers?

Daniele Zaccaria: Sometimes, farmers ask for help or technical support, and we put together a solution to address their specific challenges. Sometimes, we work with crop commodity boards, such as the Pistachio Board, the Citrus Board, the Almond Board, the Walnut Board, or the Avocado and Table Grape Commissions, to address specific production and marketing challenges. We also work on

a regular basis with state agencies, such as the California Department of Water Resources (DWR), the California Department of Food and Agriculture, or the California State Water Control Board, to address specific problems, to help design or implement incentives for growers to adopt sustainable production practices, or to help enforce resourceefficient water management policies and strategies.

Irrigation Leader: What are the main challenges facing agricultural water users in the Central Valley, and how do those differ from challenges elsewhere in California?

Daniele Zaccaria: Water quantity, water quality, and the environmental and economic sustainability of agricultural water use are growing challenges in the face of rising weather and climate variability. The magnitude of these water-related issues in the Central Valley of California is greater than in other areas of the state. The effects of weather fluctuations and weather extremes (droughts, heat waves, and so on) on crop production could normally be mitigated through irrigation. However, the available water supplies are becoming increasingly limited and restricted as a result of more frequent and prolonged droughts and of increasingly stringent environmental regulations.

Irrigation Leader: What are the most important recent advances in water management, and how are UC Davis and the UC Cooperative Extension helping farmers to adopt them?

Daniele Zaccaria: What I see as the most promising water management advances in California are the correct use of microirrigation methods for water and nutrient applications, irrigation system automation, variable-rate irrigation, fertigation, and the use of novel flow regulation and control technologies for improved water distribution among the different zones of districts’ command areas and for on-demand water delivery to farmers. The ability to forecast weather conditions 1–7 days in advance also represents a breakthrough that will help enable prospective irrigation scheduling.

However, there is a large and increasing disconnect between the on-farm water delivery requirements needed to enable the efficient use of microirrigation (in terms of timing, frequency, duration, flow rate, and pressure heads) and the water supply delivery schedules of water agencies and purveyors. This disconnect can only be addressed with diagnostic evaluations of the actual performance of water delivery services relative to on-farm needs and an appraisal of the modernization needs of existing irrigation delivery infrastructure.

Irrigation Leader: How does the Sustainable Groundwater Management Act (SGMA) factor into your work?

Daniele Zaccaria: SGMA aims to enable various overdrafted aquifers across the state to reach environmental balance between water extractions and natural or artificial recharge. That entails some readjustment of either the cropped acreage or of the water management practices for maintaining the current planted acreage. We are still coming to understand how SGMA will change the dynamics of water demand and use over space and time across the state. Some research-based information that I am collecting will help the agricultural and regulatory communities find viable water management solutions to match the available water supplies with the cropped acreage that can be farmed profitably and avoid further environmental degradation. Alternatively, land use will have to be changed to align with the available water supply and to comply with the environmental regulations. Specifically, my research findings aim to increase water productivity (more crop per drop) or to reduce the water footprint of agricultural production through the implementation of resource-efficient farming practices through optimized irrigation management, deficit irrigation practices, the use of winter cover cropping, and reduced tillage, among other methods.

Irrigation Leader: Would you discuss your other recent research?

Daniele Zaccaria: With my team at UC Davis and in collaboration with other UC faculty and academics, I conduct applied research to provide science-based information to help growers respond to drought. We also work on drought preparedness. In addition, I conduct research activities in commercial production fields to measure the actual evapotranspiration of different agronomic and horticultural crops, especially high-value specialty crops such as almonds, citrus, pistachios, and wine grapes. Over the last 6–7 years, my research team has been measuring the actual evapotranspiration in commercial production fruit and nut orchards and vineyards. We help the farming community find new ways to schedule and manage irrigation and implement efficient irrigation systems and practices to reduce the environmental footprint of irrigated agriculture. In 2018, I helped establish the California Crop Coefficient Science Collaborative (3C Science Collaborative), which is coconvened by the UC ANR and DWR and aims to improve the quality and dissemination of crop coefficient information for California crops. In 2020, I received a research grant award from a federal funding program that will enable the 3C Science Collaborative to develop a web repository of quality-ensured crop coefficient information for the 10 most water demanding crops in California, which will enhance agricultural water demand estimations and irrigation scheduling in the water-limited context of California. IL

Daniele Zaccaria is an associate professor in the department of land, air, and water resources at the University of California, Davis, and an agricultural water management specialist at the University of California Cooperative Extension. He can be contacted at dzaccaria@ucdavis.edu.