Phase I also considered agricultural adaptation strategies that addressed regional issues such as hydrology, growers’ attitudes toward climate change, and urbanization versus preservation of farmland. These topics are explored in more quantitative ways here.Since 1960, total crop acreage in Yolo County has been declining. Vegetable and orchard crop areas have increased, while field crop acreage has declined . There has been an increase in higher‐revenue‐per‐acre crops, especially a shift out of barley, and a shift into more processing tomatoes, wine grapes, and walnuts. Many factors affect changes in acreage, including changes in market conditions , input supplies, and climate. Among factors affecting acreage decisions, we investigated whether changes in climate have affected acreage allocations across crops. If responses to climate changes in the past continue to hold in the future, we can use hisorical information to learn more about how crop acreages are likely to change in response to the forecasted Yolo County climate changes from 2010 to 2050. We developed econometric models that relate acreages of each major crop to relative prices and key climate variables . The models are applied to the data including 60 years of acreage for major crops and 100 years of local climate history. Our climate history indicates that during the past century, the increase in annual temperature appears to be mainly due to warmer winters rather than to warmer summers . There was a decrease of about 150 winter chill hours in the last 100 years. Using historical reationships between climate and acreage allows investigation of how forecasted climate changes in Yolo County may affect Yolo acreage patterns. Acreage projections use climate projections for the B1 and A2 scenarios from 2010 to 2050 with GCM data from GFDL‐BCCA. Acreage projections hold constant relevant drivers of crop acreage, except for local climate variables. Among field crops,planting gutter warmer winter temperatures were projected to cause wheat acreage to decline and alfalfa acreage to rise . Thus, future decisions to increase alfalfa acreage present an interesting implication for water use: wheat uses little irrigation; whereas, alfalfa is one of the more intense water users.
By 2050, tomato acreage is projected to increase compared to the current level . This is also related to the increase in growing degree days in the winter months. A warmer climate in late winter/early spring has allowed early planting and provided favorable conditions for establishment. The forecasted climate changes have only moderate impacts on projected tree and vine crop acreage, in part because the climate changes that have occurred have not yet affected key variables enough to induce a significant change in the acreage of perennials when market conditions have been favorable. Almond acreage is projected to increase slightly with warmer temperatures in 2035–2050 . Almonds have a relatively low winter chill hour requirement. Walnut acreage, however, would decline slightly ; it has a higher winter chill requirement. This is consistent with the finding that surveyed orchard growers express concern about a decrease in winter chill hours . These projections rely on using historical relationships between acreage change and climate variables change. They are based actual past responses of acreage to climate. However, no attempt is made to forecast the relative prices, technical changes, new markets, or other factors that will also affect acreage. Water supply vulnerabilities for agriculture and other sectors can be mediated through traditional infrastructure improvements or alternative water policies . Local stewardship that is implemented by water managers and agricultural users tends to be more economical and have less environmental impact than developing new supplies. One tool that has helped water resource managers integrate climate change projections into their decision making process is the Water Evaluation and Planning system . WEAP, a modeling platform that enables integrated assessment of a watershed’s climate, hydrology, land use, infrastructure, and water management priorities , is used here for the Yolo County Flood Control and Water Conservation District service area. It covers 41 percent of the county’s irrigated area and is located in the western and central portion of the county .Recognizing the key role that land‐use planning will play in achieving the goals of AB 32, legislators passed Senate Bill 375 in 2008, requiring sustainable land‐use plans that are aligned with AB 32 .
Local governments must address GHG mitigation in the environmental impact report that accompanies any update to their general plan or carry out a specific “climate action plan” . Emissions of GHG from agriculture are often missing from existing inventory tools geared to local planners. The local government of Yolo County was among the first in California to pass a climate action plan . This project contributed to this climate action plan, and developed a set of guidelines to estimate GHG emissions from agriculture within a local inventory framework . The Tier 1 methods used here have been adapted for local activity data largely from three main sources: the California Air Resources Board Technical Support Document for the 1990–2004 California GHG Emissions Inventory ; the U.S. Environmental Protection Agency Emissions Inventory Improvement Program Guidelines ; and the 2006 IPCC Guidelines for National GHG Inventories . In Yolo County, total agricultural emissions declined by 10.4 percent between 1990 and 2008 .Lower fertilizer use was driven by two important land use trends: a 6 percent reduction in the county’s irrigated cropland; and a general shift away from crops that have high N rates coupled with an expansion in alfalfa and grape area, which require less fertilizer . In both years, emissions of CO2, N2O, and methane from diesel‐powered mobile farm equipment were responsible for 20.0 to 23.0 percent of total agricultural emissions in Yolo County between 1990 and 2008 . Fuel consumption per unit area for several important crops offset the small decline in irrigated cropland. Using the Tier 1 method prescribed by ARB, emissions of CH4 from rice cultivation were estimated to increase from 25.9 to 31.2 kilotons carbon dioxide equivalent between 1990 and 2008, entirely due to an expansion in the area under rice cultivation. Studies also suggest that cultivation practices that combine straw incorporation and winter flooding tend to generate more CH4 emissions than burning rice straw . Thus, estimates generated using the DeNitrification‐DeComposition model showed a larger increase in emissions over the study period because the Tier 3 method accounted for changes in residue and water management made in compliance with the state air quality regulations that have phased out rice straw burning, and the increase in cultivated area .
Many agricultural practices to mitigate GHG emissions offer agricultural co‐benefits. For example, economic factors are prompting local farmers to shift more of their land to crops that happen to require less N fertilizer and diesel fuel, and to adopt practices that reduce these inputs. Growers cite rising cost and market volatility of inputs, rather than mitigation per se, as a more immediate motivation to use fertilizer and fuel more efficiently. In 1990, emissions sources associated with urban areas accounted for approximately 86 percent of the total GHG emissions countywide,gutter berries while unincorporated areas supporting agriculture were responsible for 14 percent . If calculated on an area‐wide basis the county’s urban areas emitted approximately 152.0 tons CO2e per hectare per year . By contrast, this inventory results indicates that in 1990 Yolo County’s irrigated cropland averaged 2.16 t CO2e ha‐1 yr‐1 and that livestock in rangelands emitted only 0.70 t CO2e ha‐1 yr‐1 . This 70‐fold difference in the annual rate of emissions between urbanized land and irrigated cropland suggests that land‐use policies that protect existing farmland from urban development are likely to help stabilize and or reduce future GHG emissions, particularly if they are coupled with “smart growth” policies that prioritize urban infill over expansion .Many factors affect farmers’ perceptions and response to climate change; for example, characteristics of the individual farmer and their farm; social networks and involvement in programs run by local institutions, agricultural organizations, and extension services; and views on government programs and environmental policies. The goal of this sub-project is to: examine Yolo County farmers’ perceptions of climate change and its risks to agriculture; and develop a better understanding of how such factors might influence farmers’ adoption of proposed adaptation and mitigation practices. We conducted semi‐structured interviews with eleven farmers and two agricultural extension workers in the fall of 2010. The sampling strategy recruited respondents from a cross section of farm sizes, local cropping systems, and market orientations. Interviewers followed a set of open‐ended questions to minimize prompting and interviewer bias, and were used to develop a quantitative survey which was mailed to farmers in Yolo County during February and March of 2011. The survey sample was drawn from a list of 572 individuals who have submitted conventional or certified organic pesticide use permits to the Yolo County Agriculture Commissioner’s office. The final response rate was 34.0 percent. Results of the survey indicated that 54.4 percent of farmers agreed to some extent with the statement “the global climate is changing” . A minority indicated that local summer temperatures had decreased over time, while only 5.6 percent observed an increase. While contrary to statewide mean temperatures, this corresponds with local climate records which show little change in maximum summer temperature over the last century . A majority of farmers indicated that rainfall, drought, and flooding had not changed over the course of their career, but a sizable minority reported water availability had decreased and <1 percent said it had increased. In 1976, the newly constructed Indian Valley Reservoir began supplementing the District’s surface water supplies to local growers.
However, a recent drought in 2009 and 2010 reduced water releases in those years to less than 40 percent of the average for the preceding decade . The memory of this recent a drought may therefore occupy a central place in farmers’ perception of water related trends. Respondents with greater concern for drought and less reliable water were more likely to pump groundwater, drill new wells, and adopt drip irrigation . A farmer’s views on climate change affected the inclination to implement voluntary mitigation practices. More specifically, farmers who disagreed with the statement “The global climate is changing” were less likely to adopt mitigation practices than those who agreed with the statement. Likewise, skepticism that human activities are an important cause of climate change meant less inclination to adopt mitigation practices. Farmers who had frequent contact with local agricultural organizations were more likely to implement mitigation strategies Farmers are often more concerned about the future impact of government regulations than they are about the direct impacts of climate change. This ranking of concern is not surprising given the gradual nature of climate change. However, it does underscore the importance of understanding how farmers view environmental regulations and the information needed to influence their likelihood to adopt mitigation and adaptation practices. Strategies to expand the reach of local agricultural organizations and government conservation programs by improving farmer participation in their activities are thus seen as an important way to strengthen adaptation and mitigation efforts.UPlan relies on a number of demographic inputs . Attractors are given a positive value . Discouragements are given negative values . A system of weights is used to rank the attractive or discouraging property of each variable. We modified UPlan to allow development within existing urban areas, on the assumption that a significant urban redevelopment is likely within the 2010–2050 time frame. The A2 scenario loses two times more acreage of high quality soils to urbanization compared to B1 . One of the most striking findings is just how little land is required to house future populations at higher densities. The B1 and AB 32+ scenarios require 44 percent and 7 percent of the urbanized land of the A2 scenario, respectively. Even holding population increase constant at B1 levels, these scenarios use 63 percent and 38 percent of the land of the A2 scenario, most or all of it within existing urban areas, and also greatly reduce GHG emissions from transportation. These results suggest that the most important climate change mitigation policy that Yolo County could adopt would be to restrict urban development to infill locations within existing cities, and to keep existing farmland in agriculture.