Of the five initial variables, the fraction of land in cropland, the soil Storie index, and the land fraction converted to urban had high positive loading values on PC1. The close relationship between these variables is consistent with other studies that show high rates of urbanization on some of the highest quality cropland in the state . Soil salinity and the fraction of land in the 100‐yr floodplain had high positive loadings on PC2. Figure 2.4 shows the spatial distribution of land use vulnerability throughout California as measured by the sub‐ index. While relatively high land use vulnerability occurs throughout the Central Valley, areas of particular concern are the Sacramento‐San Joaquin Delta, and the corridor between the Sacramento and Fresno. In these areas of rapid change from agricultural to urban land uses, sub‐index values were frequently > 2.5 standard deviations above the mean. In the Delta region, the high vulnerability was largely due to the risks posed by both urbanization and flooding on highly productive agricultural soils. In contrast, a combination of increasing urbanization and high soil salinity were the important drivers of vulnerability further south in the San Joaquin Valley. Conversion of prime farmland to urban uses is essentially a permanent loss of agricultural potential, with many consequences for agricultural livelihoods and society at large. When urban development fragments agricultural land, farmers often lose the benefits associated with being part of an integrated farming economy; for example, sources for inputs, information sources, and processing facilities . Farming activities occurring along the urban edge can raise concerns about noise, odor, dust, and spray drift among new suburban residents, while vandalism of farm fields can cause problems for farmers . Regional and local strategies to preserve farmland and manage urban growth include strengthening agricultural zoning policies,hydroponic gutter acquisition of conservation easements on farmland, establishment of urban growth boundaries, and prioritizing infill development .

Given that greenhouse gas emissions from urban land can be more than 70 times greater per unit area than cropland , policies that preserve agricultural land will also help achieve the mitigation targets set by California’s recent suite of climate policies, namely AB 322 and SB 375.3 While the risks of flooding and soil salinization are not new to California farmers, they are likely to be exacerbated by climate change. Declining snow water storage in the Sierra Nevada is expected to increase the frequency and severity of flooding in the Central Valley . As such, efforts to help regional and district water resource managers develop accurate flood forecasts and flexible reservoir operations will further improve adaptive capacity .More than 3 million acres of irrigated farmland in California have soils with an electrical conductivity above 4 dS m‐1, a standard threshold for the occurrence of agricultural impacts . Of the acreage affected, more than two‐thirds is located in the San Joaquin Valley. In these areas, various irrigation methods can be used to leach salts out of the crop’s rooting zone . But since salts can still accumulate along the margins of the wetted area, growers must often apply water in excess of crop needs to ensure that salts are sufficiently leached . The installation of systems to drain, reuse, and dispose of saline effluent are also options, though high costs and a lack of suitable disposal sites remain important barriers .Results of the PCA for the socioeconomic vulnerability sub‐index indicate that 70.3 percent of the cumulative variance among grid cells is accounted for by retaining three principal components . Seasonal and migrant farm workers, loss of farms, and farm disaster payments all had high positive loadings on PC1, while loss of farm jobs and the social vulnerability index loaded highly on PC2. The commodity concentration was largely independent of these other factors, as indicated by its high positive loading on PC3. Three counties along California’s Central Coast all had socioeconomic sub‐index values greater than 1.5 standard deviations above the mean . The high vulnerability of these counties was due to two main factors: the high rate of disaster payments per unit of cropland; and the large number of seasonal and migrant farm workers per unit of cropland. A closer look at the agriculture in these counties reveals that while each have only a small amount of cropland, the mild coastal climate allows them to devote a large fraction to vegetable and berry crops. Since these tend to be high‐value crops that require more labor, it follows that disaster payments and the number farm workers per unit of cropland area are also higher.

Larger counties such as Monterey, San Joaquin, Imperial, and San Bernardino had moderately high socioeconomic vulnerability due to some of the same factors. In Yuba, Sutter, and Madera counties vulnerability was driven by a combination of high disaster payments and a loss of farm jobs. The main factor influencing the high vulnerability in Mendocino County and the moderately high vulnerability in Napa and Sonoma counties was their high Herfindahl index values, which captured the heavy concentration of wine grape production in this region. While disaster payments are used here as an indicator of vulnerability, the federal programs that provide these payments are generally seen as a way to help farmers cope with risk and strengthen their adaptive capacity. Since many fruit and vegetable crops receive no federal subsidies, disaster payments and crop insurance are among the few remaining options for specialty crop producers . However, as agricultural support programs receive greater scrutiny under tightening state and federal budgets, studies that examine the impact of potential reforms and their effects on vulnerability are needed. In contrast to government programs, the advantage of diversification to new crops, products, markets, or income sources is that farmers have more control over the outcome. But while diversification can help spread risk and facilitate a shift toward new crops should the need arise, concerted efforts to improve knowledge‐sharing among stakeholders will be needed to overcome the risks and trade offs associated with unfamiliar cropping systems and market opportunities .Figure 2.6 provides an illustration of total agricultural vulnerability statewide by integrating the four sub‐indices into one total AVI index. Based on this analysis, moderate vulnerability exists in most of California’s agricultural lands, which suggests that there is a need for all agricultural communities to begin to develop adaptation plans that address the potential impact of changing climate, land use and economic factors. Many local and regional governments are now developing climate action plans that accompany updates to their general plans . To date, these climate action plans have mostly focused on greenhouse gas mitigation, but the results presented here suggest that adaptation should hold an equally important place in local planning activities. The total AVI also suggests that there are several regions of concern that merit careful consideration.

These include the Sacramento‐San Joaquin Delta, the Salinas Valley, the corridor between Merced and Fresno, and the Imperial Valley, which all had a mix of high and very vulnerability. While the sub‐indices discussed above help to highlight the location‐specific factors contributing to these regions’ overall vulnerability, the indexing method used in this study is inherently coarse. Given this limitation, future studies that follow a “place‐based” approach will be needed in order to understand the unique local characteristics, both biophysical and socioeconomic, that may contribute to improved resilience within agricultural communities. The recently completed case study of agricultural adaptation to climate change in Yolo County, summarized in Section 3 below, is an early example of how to integrate these elements .While the AVI presented above represents an early a proof of concept, significant gaps remain in the set of potential variables that could be included in the index. In particular,u planting gutter future iterations of the AVI will need to consider additional variables that more fully assess the vulnerabilities to California’s water resources and livestock systems in a spatially explicit manner. For livestock, studies that evaluate statewide spatial variation in the season length of adequate forage and its links with winter precipitation may be a useful addition . These are but a few of the many types of spatial datasets that might be integrated in to the California AVI. In its current form, the AVI is designed to assess “present” agricultural vulnerability. However, going forward there is potential to modify the AVI so that it can accommodate future projections of climate, land use, and socioeconomic variables. For example, integrating down scaled climate projections into the climate vulnerability sub‐index, or integrating statewide UPlan runs into the land use vulnerability sub‐index, are very feasible next steps . Yet, since many of the biophysical and socioeconomic factors included in the sub‐indices can vary unpredictably over time, and in some cases have not been accurately modeled into future, use of the AVI to examine future scenarios may have inherent limitations. To overcome the potential limits, contributions of expertise and data from a broad range of stakeholders, government agencies, and academic disciplines will no doubt be required.Preservation of agricultural land is a priority in Yolo County, and planning is focused on regional land use guidelines that maintain land in agricultural production and concentrate new development into urban areas. Regions within Yolo County are distinguished by their land forms , proximity to the Sacramento River and Delta , water availability , and the influence of small towns and cities . There is greater prevalence of wine grapes along the river, processing tomatoes in the alluvial plains, and organic fruits and vegetables in an isolated, narrow valley to the north. Flooding along the Sacramento River poses the most significant regional hazard from climate change; water flows will increase by at least 25 percent by 2050 due to a decrease in snow pack in the Sierra Nevada . As for most of California during the past few decades, there has been a trajectory toward less crop diversity, larger farm sizes, but fairly stable markets for commodities . Most commodities are managed with high intensification of agricultural inputs . The number of organic farms, however, is growing. A recent survey showed that many riparian corridors have low scores for soil quality and riparian health , and there is concern about transport of pesticides to the San Francisco Bay delta .

Environmental quality is now receiving more attention with active grower participation in programs from several agencies.Phase I of this case study examined possible effects of increased temperature and decreased precipitation on Yolo County crops . The horticultural “warm‐season” crops in the county will experience more stress than field crops, due to greater environmental sensitivity of their reproductive biology, water content, visual appearance, and flavor quality. New horticultural crops may include “hot‐season’ crops in summer, and “cool‐ season” crops that prefer warmer winters. Expansion of citrus and of heat and drought‐tolerant trees are likely partly because fewer winter chill hours will be difficult for some stone fruits and nuts . Forage production for livestock in upland grasslands may increase with warmer temperatures during the winter rainy season, but field experiments with elevated carbon dioxide do not corroborate this expectation . More nitrogen limitation will likely occur under eCO2 , unless N‐fixing legumes become more abundant. During the past 25 years, crop diversity has decreased across Yolo County , but resilience to extreme events, such as heat waves, may be enhanced in the future by a more diverse crop mix that varies in stress tolerance. Water supply has been considered the most uncertain aspect of climate change for farmers in Yolo County, who rely on groundwater for about 30 to 40 percent of their supply in a normal water year .Discussions with the Yolo County UC Cooperative Extension farm advisors indicate special concern for stripe rust on wheat , insectpests on nuts, medfly, corn earworm on tomato, tomato spotted wilt virus, stem nematode on alfalfa, and earlier activity of perennial weeds such as bindweed . Crop management is subject to change to improve production and environmental quality. Phase I evaluated a set of practices and found that most practices either benefitted GHG mitigation or benefitted adaptation to a changing climate. More comprehensive analysis of these complex relationships is needed.