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The substantial threat of concurrent air pollutants to public health is increasingly severe under climate change. To identify the common drivers and extent of spatiotemporal similarity of PM 2.5 and ozone (O 3), this paper proposed a log Gaussian–Gumbel Bayesian hierarchical model allowing for sharing a stochastic partial differential equation and autoregressive model of order one (SPDE-AR(1)) spatiotemporal interaction structure. The proposed model, implemented by the approach of integrated nested Laplace approximation (INLA), outperforms in terms of estimation accuracy and prediction capacity for its increased parsimony and reduced uncertainty, especially for the shared O 3 sub-model. Besides the consistently significant influence of temperature (positive), extreme drought (positive), fire burnt area (positive), gross domestic product (GDP) per capita (positive), and wind speed (negative) on both PM 2.5 and O 3 , surface pressure and precipitation demonstrate positive associations with PM 2.5 and O 3 , respectively. While population density relates to neither. In addition, our results demonstrate similar spatiotemporal interactions between PM 2.5 and O 3 , indicating that the spatial and temporal variations of these pollutants show relatively considerable consistency in California. Finally, with the aid of the excursion function, we see that the areas around the intersection of San Luis Obispo and Santa Barbara counties are likely to exceed the unhealthy O 3 level for USG simultaneously with other areas throughout the year. Our findings provide new insights for regional and seasonal strategies in the co-control of PM 2.5 and O 3. Our methodology is expected to be utilized when interest lies in multiple interrelated processes in the fields of environment and epidemiology. [Display omitted] • PM 2.5 and O 3 pollutants are jointly analysed in California through a log Gaussian–Gumbel Bayesian hierarchical joint model. • Distinct spatiotemporal interactions are revealed with a shared SPDE-AR structure; common drivers of PM 2.5 and O 3 are identified. • Hotspots at risk of simultaneously exceeding unhealthy O 3 levels are identified. [ABSTRACT FROM AUTHOR]

The licensed cannabis industry represents one of the top five most economically valued agricultural commodities in California, yet farming largely remains on remote, environmentally sensitive, "marginal" lands. Using mixed methods, this paper examines the determinants of this marginalization, their embedded elaboration, and their relation to historical policy regimes. We used Generalized Additive Models (GAMs) to determine the most important predictors of licensed cannabis industry development since the inception of a statewide licensing program in 2018 and to compare the distribution of licensed cannabis to other forms of rural agriculture, including vineyards and pasture, to understand landscape factors and environmental sensitivity of land uses. We found that a county's median income and the extent of traditional (non-cannabis) agriculture, as measured by the proportion of on-farm (non-cannabis) employment, were both negatively associated with its amount of licensed cannabis agriculture. Ethnographic data suggests that cannabis is often excluded from traditional agricultural areas, through formal local-level bans, restrictive zoning, high "prime" farmland values, and cultural exclusions from other powerful resource users. The resulting relegation to "marginal" lands foments conflicts with amenity land users and environmentalists, even as it partly supports "legacy" cultivators whose farms were established under prior policy regimes. Results suggest that cannabis is more likely to be grown under conditions that introduce regulatory hurdles, including farming on steeper slopes, with natural streams onsite, and without access to large groundwater aquifers for irrigation. Our findings suggest that failure to allow licensed cannabis farming in traditional agriculture regions has led to a self-fulfilling prophecy wherein cannabis cultivation is largely relegated to environmentally sensitive areas where cultivation activity has an elevated tendency for environmental impacts. • Cannabis cultivation occurs outside conventional agricultural areas on "marginal" land. • Counties with higher incomes and more traditional agriculture issue fewer licenses. • Non-cannabis land users drive cannabis licensing restrictions. • Marginalization of cannabis produces environmental conflict and marginalizes farmers. • Marginal land use is socially and geographically produced. [ABSTRACT FROM AUTHOR]

Various tools and techniques are used by environmental managers and planning agencies to make land use decisions that balance different and often competing goals. Multiple goals, or objectives, are generally challenging to address because there is likely no single optimal solution, but rather a range of possible Pareto (or tradeoff) solutions. Considerable attention has focused on software and approaches that rely on heuristic methods to generate solutions for land use planning problems with multiple objectives. While fast and accessible, there remain uncertainties about the quality of solutions obtained by these heuristic methods and whether they are indeed meeting the needs of environmental managers. This paper explores forest treatment planning for wildfire risk mitigation seeking to balance multiple objectives when the spatial pattern of treatment is restricted. Solution quality of one widely employed forest planning tool is evaluated (using measures of completeness, inferiority, and maximum gap) under a range of geographic settings and problem sizes. The findings indicate that obtained solutions are suboptimal, and fail to represent the full spectrum of tradeoffs possible. • Demonstrates that a forest planning tool may provide solutions which differ significantly from the optimal solution set when balancing multiple objectives • Assesses quality of heuristic solutions across several geographic applications • Presents case study in a national forest in California, USA [ABSTRACT FROM AUTHOR]

Agriculture dominates California's San Joaquin Valley with over five million acres of farmland produces 400 different commodities ranging from nuts, tree fruits, vines, and row crops. During dry years agricultural production in the San Joaquin Valley uses about 53% of total applied water in the state. Implementation of California's Sustainable Groundwater Management Act (SGMA) will restrict groundwater pumping, likely reducing irrigated agricultural land use resulting in conversion to alternative land uses. To promote collaborative and inclusive efforts to repurpose agricultural land, California's legislature established a funding program administered by the Department of Conservation, the Multibenefit Land Repurposing Program (MLRP), in 2021. To ensure that land repurposing plans under the MLRP and SGMA represent San Joaquin Valley community needs this paper examines public perceptions of future land uses under SGMA through a phone survey. Respondents (n = 197) were recruited through a stratified random sample of mobile numbers registered within communities in the San Joaquin Valley classified as disadvantaged communities (DACs) (n = 32). Our results show that most respondents were somewhat (33%) or not at all (54%) familiar with SGMA, highlighting the need for outreach efforts to overcome barriers to representation, translation, and education about future water and land use decisions. Survey respondents identified secure water supplies (e.g., groundwater recharge) (35%) and less-water intensive agriculture (27%) as their top land use priorities to address groundwater overdraft under SGMA, indicating that the status quo for land use is preferred to alternative land uses. Preference for maintaining agriculture as primary land use (27%), we correlated with agricultural identity and lack of interest in community or global benefits such as schools and climate change mitigation. The findings from this study underscore the local variability in land use values and the importance to engaging local communities in land use decision-making, especially as they relate to changing current practices toward a more climate-resilient but agriculturally productive future with less land and less water. [Display omitted] • Most respondents were not familiar with the 2014 California Sustainable Groundwater Management Act (SGMA). • Respondents showed a high level of support for groundwater recharge for economic and community well-being. • Secure water supplies and less water-intensive agriculture were perceived as important land use priorities. • The role of agriculture in the local economy and climate change impacts were given higher priority than other land uses. • Outreach efforts need to overcome barriers to representation related to education and language to increase DAC inclusion. [ABSTRACT FROM AUTHOR]

Agricultural regions in the United States are experimenting with sustainability partnerships that, among other goals, seek to improve growers' ability to manage their vineyards sustainably. In this paper, we analyze the association between winegrape grower participation in sustainability partnership activities and practice adoption in three winegrowing regions of California. Using data gathered from a survey of 822 winegrape growers, we find a positive association between participation and adoption of sustainable practices, which holds most strongly for practices in which the perceived private benefits outweigh the costs, and for growers with relatively dense social networks. We highlight the mechanisms by which partnerships may catalyze sustainable farm management, and discuss the implications of these findings for improving sustainability partnerships. Taken together, we provide one of the most comprehensive quantitative analyses to date regarding the effectiveness of agricultural sustainability partnerships for improving farm management. [ABSTRACT FROM AUTHOR]

A key component of California's cap-and-trade program is the use of carbon offsets as compliance instruments for reducing statewide GHG emissions. Under this program, offsets are tradable credits representing real, verifiable, quantifiable, enforceable, permanent, and additional reductions or removals of GHG emissions. This paper focuses on the permanence and additionality standards for offset credits as defined and operationalized in California's Compliance Offset Protocol for U.S. Forest Projects. Drawing on a review of the protocol, interviews, current offset projects, and existing literature, we discuss how additionality and permanence standards relate to project participation and overall program effectiveness. Specifically, we provide an overview of offset credits as compliance instruments in California's cap-and-trade program, the timeline for a forest offset project, and the factors shaping participation in offset projects. We then discuss the implications of permanence and additionality at both the project and program levels. Largely consistent with previous work, we find that stringent standards for permanent and additional project activities can present barriers to participation, but also, that there may be a trade-off between project quality and quantity (i.e. levels of participation) when considering overall program effectiveness. We summarize what this implies for California's forest offset program and provide suggestions for improvements in light of potential program diffusion and policy learning. [ABSTRACT FROM AUTHOR]

Expansive clays are found in many countries worldwide, and they exhibit inherent volume change during the seasonal moisture variation causing cracks, heaves, and damages to the overlying pavements. Chemical stabilisation is one of the most used approaches to treat the expansive clay subgrades. Cement, Lime and Fly ash are the most commonly used stabilisers, in which fly is cheaper and a by-product obtained from the coal power plant. This paper reviews fly ash stabilisation on various clay types, including low plasticity clays, high plasticity clays, silty clays, organic clays, and peats. The review begins with the properties of fly ash, followed by the characteristics of fly ash stabilised subgrades. The micro-level mechanism, physical, mechanical, and hydraulic characteristics of stabilised pavements are presented graphically for the Class C, and F fly ashes. The micro-level studies reveal that the pozzolanic reaction is stronger than the cation exchange during the fly ash stabilisation. The unconfined compressive strength (UCS), California bearing ratio (CBR) and resilient modulus (M r) increased with the fly ash addition and curing time for most soft soils except peat clays. Based on the mechanical and hydraulic characteristics, using 15% class C fly ash with 7 days of curing is recommended for optimum performance. Although few research studies confirm that the leachate limit of stabilised soil is within the acceptable limit, further studies are required to investigate the uptake of heavy metals and other certain carcinogenic contaminants. This study will provide key information for researchers and Engineers on the selection of fly ash stabilisation measures for expansive subgrades. • The effects of fly ash stabilisation on different types of expansive clays are compared. • The mechanical, hydraulic and durability characteristics after stabilisation are reviewed. • Both class C and F fly ashes drastically reduce the swelling potential of clays. • The pozzolanic reaction is more influential than cation exchange in fly ash stabilisation. [ABSTRACT FROM AUTHOR]

In this paper, we ask how the written composition of public policies structure an environmental governance system. We answer this question using semi-automated text analyses of 22 state-level policies governing oil and gas development in California between 2007 and 2017. The findings portray an environmental governance system that is both partitioned and connected into different focal areas (called "targeted action situations") through certain actors, issues, and rules. We conclude with substantive insights about California's oil and gas governance system, as well as theoretical and methodological contributions for analyzing the composition of public policy to advance knowledge about hybrid governance. • A coercive or regulatory form of governing system can appear responsive to signals in its environment. • Policy-making venues produce policies that connect actors in the broader governance system via targeted action situations. • Interdependent action situations are connected in multiple ways. • The actors, issues, and rules in a governance system tend to partition or connect the system. • The institutional grammar can be adapted to study public policies. [ABSTRACT FROM AUTHOR]

In regions experiencing aquifer depletion, planning for groundwater sustainability requires both accurate accounting of current groundwater budgets and an assessment of future conditions, with changes in recharge and pumping. Hydrologic variability, climate change effects on water flows, changing water infrastructure operations, and inherent uncertainties in modeling, challenge the plans to achieve groundwater sustainability. This paper examines the importance, magnitude, and policy implications of uncertainties in groundwater overdraft estimation for water management in California. We review water balance estimates from two regional-scale groundwater models—C2VSim and CVHM—for sub-regions within California's Central Valley, and examine the variability and uncertainty in historical and future estimates of groundwater overdraft. Assuming reductions in agricultural water use for sub-regions with overdraft, we estimate the probabilities of ending groundwater overdraft for different periods. We also obtain the economic costs associated with these reductions in agricultural production. Results from both groundwater models show significant inter-annual variability in flows affecting groundwater storage, and our model comparison highlights the uncertainty in water budget estimates for Central Valley sub-regions given the differences between models. The analysis of the probabilities of achieving sustainability at the sub-regional scale show that the average overdraft rate is important and that greater variance in annual groundwater storage increases uncertainties in ending overdraft, especially for shorter periods. Greater reductions in annual net water increases the reliability of achieving groundwater sustainability, but rising rapidly agricultural economic losses. Setting management thresholds below groundwater levels can ease meeting sustainability criteria, but also can introduce a false pathway to sustainability. Finally, we discuss policy implications for the design of local groundwater sustainability plans and state assessment and regulation of local plans. • Many regions in California's Central Valley use groundwater unsustainably. • Uncertainty in models and future hydrology challenge groundwater sustainability. • Comparison of models shows significant uncertainty in estimates for water budgets. • Less water use increases sustainable paths but also agricultural economic losses. • Consideration of uncertainty and costs is essential for planning for sustainability. [ABSTRACT FROM AUTHOR]

The process of expanding a network of conservation areas includes identifying valuable areas for conservation, devising policies and implementing conservation actions on the ground. While the first two components are often analyzed in conservation science, the literature seldom focuses on the implementation process, particularly, how the governance structure acts as driver of conservation outcomes. In this paper, we analyze the process of development of the conservation network in California between 1910 and 2010 to test whether governance structure explains the variation in the attribution of land for conservation over time. We find that governance structure does play an important role in the development of the conservation network over the century. We find evidence that polycentric and diverse governance structures result in better conservation outcomes (i.e. more area of land acquired for conservation). Arrangements that included multiple levels of agencies (e.g. Federal, State, and County) better predict the area of conservation land per decade. Location of conservation action per county had an effect on conservation outcomes over the last decades, and we also find a strong negative effect of per capita income in the implementation of conservation actions. These results suggest that it is possible to leverage governance structure to meet future conservation challenges through the maintenance of a diverse and polycentric governance structure. • We conduct a longitudinal study on polycentric governance for conservation. • We find evidence for polycentric governance leading to more conservation outcomes. • Different governance structures matter in different points in time due to legacies. • Conservation outcomes are hindered by economic factors and land competition. • Governance structure might be leveraged to meet future conservation challenges. [ABSTRACT FROM AUTHOR]

Winter cover crops could contribute to more sustainable agricultural production and increase resiliency to climate change; however, their adoption remains low in California. This paper seeks to understand barriers to winter cover crop adoption by monetizing their long-term economic and agronomic impacts on farm profitability in two of California's specialty crop systems: processing tomatoes and almonds. Our modeling effort provides a present, discounted valuation of the long-term use of winter cover crops through a cost-benefit analysis. A net present value model estimates the cumulative economic value of this practice. We then explore how the long-term trade-offs associated with winter cover crops can affect an operation's profits under a spectrum of hypothetical changes in California's agricultural landscape. Our analysis sheds light on the barriers to adoption by reporting benefit-cost ratios that indicate profitability across several scenarios; however, benefits and costs accrue differently over time and with long planning horizons. At the same time, a small portion of gained benefits are external to the grower. Findings from this study reveal that winter cover crops in California can be profitable in the long-term, but the extent of profit depends on the cropping system, extent of irrigation savings due to improved soil function, access to financial subsidies and climate change. Winter cover crops can return positive net benefits to growers who have flexible contractual obligations, can wait for the long-term return on investment and manage cover crops as closely as cash crops. This analysis contributes to the study of conservation agriculture practices by explaining possible reasons for low adoption through an economic valuation of the implications of soil management choices and policy counterfactuals. • Net present value models were used to understand winter cover crop adoption in California. • Winter cover cropping can increase baseline profits in specialty crop systems sometimes. • The value of winter cover crops accrues over many planting seasons. • Reduced irrigation and increased subsidies can increase adoption of cover crops. [ABSTRACT FROM AUTHOR]