Factors such as the degree of diversification in a region’s economy, prosperity in the region, as well as the size, number, and conditions of the transfers play a role in influencing the magnitude of the regional impacts. Concerns over third-party effects were instrument in IID’s decision to put conditions on its water transfers under the QSA—they limited the extent of land fallowing and required that water transfers to eventually be sourced from on-farm conservation. Strategies to combat such concerns over third party effects likely involve a variety of approaches including social programs and support for land repurposing . Land repurposing as a response to the likely reductions in irrigated cropland is gaining significant attention in California . Developing solar energy, restoring desert and upland habitat, or riparian and wetland areas, expanding water-limited crops, or developing water-efficient urban development in formerly irrigated areas are all possible options for repurposing . In addition, conservation incentive programs could help mitigate the impacts of fallowing on ecosystems and people, and redistributing irrigation water onto fewer irrigated acreage should consider ecosystem services of alternative uses to maintain multifunctional landscapes in a changing climate.Augmenting water supplies through importing water from other regions, or further tapping into local surface or groundwater supplies, are limited at best. Yet supply augmentation options do exist, albeit likely at a higher cost . A portfolio of options needs to be considered, plastic grow pots including better capture and use of flood water, maintaining healthy soils, and more effective monitoring, surveillance, and response to extreme weather events.

Groundwater recharge , water recycling and reuse, and desalination provide opportunities to enhance supply. Increasing the operational efficiency of surface or groundwater storage and transport can also increase water availability. Last, water trading can help reallocate water supplies to reduce costs of both temporary and long-term shortfalls . Groundwater recharge. Managed aquifer recharge is the intentional recharge of water to aquifers for subsequent recovery or environmental benefit . MAR practices have been used in California in its operation of water banks–aquifers used for underground storage–and to avoid saltwater intrusion in aquifers in coastal zones. There is now renewed interest in developing MAR efforts to catch flood flows, especially for its low financial and environmental cost compared to other alternatives . The California Department of Water Resources found that an annual average of almost 2,000 hm3 is available for recharge using current infrastructure without interfering with environmental regulations. Adding new infrastructure could increase recharge opportunities in nearly all California regions over time, and particularly in the Sacramento Valley where significant opportunities exist . The flows that comprise the recharge are often available in large magnitudes for short periods and thus present challenges due to regulation and infrastructure. Current storage and conveyance infrastructure as well as operational and regulatory practices need to be expanded and improved to make full use of this water supply augmentation option. Although most water volumes have been recharged in dedicated basins in California, there is also much interest for on-farm recharge . By recharging water directly on farms, current irrigation infrastructure could be used, thus reducing the costs. Institutional challenges include lack of incentives for farms to accept flows because the individual farm benefits may be small relative to the public benefits.

Additionally, some crops likely are better suited for this than others, e.g., crops that are dormant in winter–such as almonds and vines–may not be negatively impacted by this practice. Additional research on recharge issues is needed to better understand the effects of on-farm recharge on crop yields, water quality, and soil health, among other factors .Wastewater recycling . The California State Water Resources Control Board estimates that 900 hm3 of wastewater was recycled in California in 2020 , with 250 hm3 being used for agriculture. In 2020, the state published its California Water Resilience Portfolio , which aims to recycle and reuse 3,100 hm3 over the next decade. Most of the wastewater in the CV is already being used with further treatment by downstream users or the environment. Therefore, the most promising locations for wastewater reuse and recycling are in Coastal California, where much of the wastewater is not being reused. Furthermore, while wastewater quality varies significantly across sources with more highly polluted water needing more costly treatment, some of those costs might be avoided for some farm uses . Desalination. Salty water can be treated to make it suitable for urban or agricultural use. In California and other western states, desalination has mostly been used to remove salts from brackish water. The lower constituent concentrations in brackish water make the process less costly than ocean desalination and, thus, more feasible for farm use. Currently, 14 seawater desalination plants are spread across California producing 110 hm3 , with another 23 brackish groundwater desalination plants producing 173 hm3 . There are plans to desalinate another 35 hm3 of seawater by 2030 and 104 hm3 of brackish water by 2040. These quantities contribute a small fraction to the overall water supply in California. Also, the infrastructure and energy costs of seawater desalination remain high particularly for agriculture, even without consideration of the likewise costly mitigation of negative environmental effects. Some have identified inland non-seawater desalination as lower cost alternative , yet brine disposal costs at the operation scale needed for irrigation may remain a challenge.

Seawater desalination is mostly used in urban areas of Southern California and the Central Coast, where alternatives are even more expensive. Water trading. California has a small active water market where buyers and sellers trade water . These trades– ranging from 2 to 5% of all water used by cities and farms, reduce the economic costs of shortfalls during droughts and accommodate geographic shifts in water demand, enhancing flexibility in water management . Studies have found that trading could bring significant benefits to agriculture, the environment, and urban users in California . The benefits of an expanded water market grow as water scarcity intensifies, which is likely given the transition to sustainable groundwater use and the reduction in water availability driven by climate change . But a combination of aging infrastructure and complex, conflicting regulatory structures, including volume limits, hinder the expansion of trading . Improving market design, addressing impacts on third parties, securing stakeholder buy-in, and reducing transaction costs are needed to improve California’s water market . Of course, increasing water demand by cities may further drive water from agriculture to cities through water trading agreements . The Mix of Supply- and Demand-Side Options. The combination of supply- and demand-side options will shape the evolution of California’s agriculture. With the expected water availability declines, expanding supplies could mitigate the reduction of California’s agricultural output. But economic pressures constrain supply expansion, as most supply options are too expensive for crop irrigation, which is profitable only if the revenues of the expansion outweigh the opportunity costs . Water trading should incentivize supply expansion, as trading allows water to move to higher profit cropping locations. Federal and state investments can also propel supply expansion. An economic assessment of supply- and demand-side options in the SJV found that around 500 hm3 of supply expansion might be efficiency enhancing—i.e., willingness to pay for supplies is greater than the costs. While 500 hm3 only represents a quarter of the expected decline in water availability, demand reduction will comprise most of the adaptation. Other regions will have different constraints and options. In the Sacramento Valley there will be less water availability declines and more options for groundwater recharge, resulting in less demand reduction. In the Central Coast, high-value crops are more likely to pay for expensive supply options , but even there some demand reductions are likely. In the South Coast, growth of urban demands and the reductions in Colorado water allocations will likely be met by reduced irrigated acreage, although supply expansion partnerships between local farms and urban interests might be feasible . Cropping System Design. For better performance, big plastic pots water stewardship must be accompanied by cropping system adaptations to climate change that reduce water use while regenerating natural resources, maintaining food production, and allowing farms and ranches to build resilience mechanisms. Adapting crop management practices are a main entry point for adaptation through changes in crop location, planting schedules, genotypes, and irrigation . The large range of crops grown in California allows for crop switching based on vulnerability assessments and ecosystem service provision . Management complexities, response to market demand, and downstream infrastructure often make such system adjustments difficult to implement and coordinate at the watershed scale to improve water use and conservation measures. Reallocation of water resources to perennial crops has increased in recent decades with drought-year fallowing of annual cropland.

More comprehensive system-based solutions would create incentives to keep soil covered to provide cobenefits for long-term sustainability with low potential tradeoffs for water use . With climate change, perennial crops are increasingly exposed to year-long stressors that increase their need for irrigation and present growers with less adaptation options to annual variability, such as Relocation and replacing tree species/cultivars . Careful implementation of low-volume irrigation systems is crucial to avoid negative implications on groundwater recharge. Moreover, while subsurface drip irrigation enhances field and plant scale water use efficiency compared to flood irrigation, drip systems can degrade soil health properties important for water infiltration and runoff control, salinity mitigation, and carbon sequestration within the soil profile . While efficiency and technology replacements have a role to play in optimizing water use; they seldom address the ecological, economic, and social drivers of vulnerability Effective adaptation measures must therefore be system based and consider the complex socioecological interactions at play to ensure climate smart outcomes . There is growing evidence that ecosystem-based adaptation options such as cropping system diversification can support adaptation while storing carbon, supporting biodiversity, and securing ecosystem services . This is especially relevant for both California’s organic crop production, and horticultural systems which tend to be more reliant on ecosystem services for pollination and bio-control than field crops. Managing for diversity and flexibility rather than simplification and consolidation enhances adaptive capacity by improving responsiveness to climate changes, lowering vulnerability, and allowing portfolio effects to mitigate impact of disturbances . Diversification using inter-cropping, longer crop rotation, or integrated crop livestock designs have been shown to support water regulation and buffering of temperature extremes as well as other ecosystem benefits which can in turn mediate yield stability and reduce risk of crop loss . Improvements in soil health associated with organic carbon inputs, soil cover, and diversification can mediate groundwater recharge and water and nutrient retention to mitigate yield loss under drought . However, tradeoffs and benefits of ecosystem-based approaches for adaptation and mitigation are context specific, and rigorous assessments of adaptive gains and water footprints are needed. As water scarcity and associated changes in crops and landscape structures unfold, developing approaches that exploit the interconnectedness of diversity at fields, operations, landscapes and food system scales with healthy ecosystems and communities will be critical for sustainable and equitable transitions.Responding to climate change and the accompanying challenges facing agriculture in California is most effectively accomplished with inclusive and innovative approaches involving farm and rural stakeholders and policymakers using information and tools from researchers and advisors. With effective adjustments in response to climate and related water supply and demand concerns, California agriculture can become more economically, socially, and environmentally sustainable in the future. Water is central to that future. Government water management and planning in California has long been institutionally and geographically decentralized. Many local irrigation districts and SGMA groundwater sustainability agencies develop, implement, and maintain plans to weather recurrent droughts and floods. Agencies attempt to facilitate system-wide flexibility in water allocation, which can improve resilience in the case of climate extremes. There is also a role for agencies to improve coordination among stakeholders and facilitate flexibility to allow water to flow where it contributes most to economic, environmental, and social goals. Unfortunately, these broad benefits often are not within the mandate of local agencies. Furthermore, devolution in water management to local agencies rather than to watershed-level governance, creates natural conflicts where one agency’s goals or actions may create conflict and externalities with another nearby agency given water often extends beyond any single agency’s political boundaries.