The second of these layers includes existing residential neighborhoods, which typically consist of small parcels of land owned by residents who are highly resistant to redevelopment, unless in the context of adding second units to existing houses. Even the process of creating secondary units tends to be slow and to produce relatively few units, despite some municipal programs to encourage it. Commercial and industrial land uses and apartment buildings are likely to be located near major and minor arterials and freeway ramps. Low‐density residential development is more likely to occur at a distance from these roads due to noise and traffic concerns. Mid‐ to high‐density residential development is likely to be attracted to downtown locations, neighborhood centers, and shopping centers; especially in the low‐GHG emissions scenarios in which public policy focuses on redeveloping and building up existing urban centers. Mid‐ to high‐density residential development is also likely to be attracted to railroad stations in these scenarios as new passenger service is added and public policy emphasizes “transit‐oriented development.” Some industrial development is likely to locate near railroad lines in these scenarios, since rail offers more energy‐efficient transportation of many goods. We assumed that locations currently slated for development that are distant from existing cities County, such as the Dunnigan area along Interstate 5 in the north of the county, will serve as urbanization attractors only in the scenario with higher GHG emissions. Census blocks with recent development are distributed fairly evenly between rural and urban areas of the county. We assumed that these blocks with recent growth would attract more urbanization in the future. This is in part because these areas are likely to possess infrastructure such as roads, water lines, sewer mains, and power lines which make development easier and cheaper.
It is also because these areas are likely to contain previously subdivided parcels of land that are not yet built upon,nft hydroponic and land owners that are more interested in subdividing, selling, or building on the land. In scenario with higher GHG emissions, in which planning controls are weaker, census blocks with growth will be a stronger attractor, particularly in exurban locations. In the lower GHG emissions scenarios they will play a weaker role in attracting urbanization, since public policy is more likely to protect non‐urban land, and less left‐over land is likely within urban areas. Previously, our larger research team developed a set of story lines for scenarios reflecting different climate change and urbanization policies for Yolo County in 2050 . These were intended to emulate for the county story lines developed in 2000 by the IPCC , with the addition of a scenario with very low GHG emissions corresponding to an even more stringent policy direction than established by California’s AB 32 legislation. Each scenario corresponds to a broad‐brush story line, which is built upon a set of political, economic, institutional, and demographic assumptions. Each story line is a possible future for urban growth and emissions for the county.As in IPCC scenario A2 , our A2 scenario assumes that population growth would remain high, with an approximate doubling of the current county population to 394,000 . With an increase in population, continued economic growth and technological innovation, the county would see urbanized areas increase by 50 percent. Current preservation and land use policies would remain in place and although new suburban subdivisions would be built, there would be some focus on improving land use through greater land use mix, higher densities, and more infill, and limiting sprawl. Agricultural land would be lost to urbanization while less participation in farmland preservation programs, such as the Williamson Act, would result in less farm acreage and fewer farmers. Even with an increase in population, vehicle miles traveled would remain stable through land use and pricing changes, increased use of alternative modes, and greater fuel efficiencies. Still, the A2 story line would be fossil fuel intensive as a result of more drivers and the dominance of automobiles as the main transportation mode.
In terms of climate, under A2, average temperatures are predicted to increase between 1°C and 3°C for 2050. Changes in cropping systems and technological support for agriculture would continue in about the same way as present, without major societal investment in alternative options to deal with the impacts of global warming. The A2 story line is a near continuation of current demographic, economic, technological, and environmental developments with some improvements and responses to current issues being addressed and implemented. We should emphasize that in terms of suburban sprawl, the A2 story line is by no means a worst‐case scenario. Rather, it should be seen as a continuation of practices in the 1990 to 2010 period. If this story line had been based on prevailing development patterns from 1950 to 1990, suburban densities would be in the range of 4–6 units per acre instead of 8, less development would occur in medium‐ and high‐density forms, and a higher percentage of larger 1–10 acre ranchettes would be created. Suburban sprawl would cover a much larger percentage of the county in that case, taking far more agricultural land out of production. In IPCC scenario B1 , societies become more conscious of environmental problems and climate change, and sustainable development efforts are implemented. Under our Yolo County B1 story line, population would grow slowly, reaching a mid‐range population size of 335,000 by 2050 . Economic development would be moderate, with a shift from the production of goods to a more service‐based economy that is connected to the larger global economy. Technological innovation remains high in the Sacramento region, with an emphasis on small‐scale, green technologies. B1 is a relatively low GHG emissions scenario in which the urban area extends only 20 percent as a result of compact growth through higher densities, increased infill, and a focus on small, locally owned retail stores rather than big box developments that require more driving. As current transportation and emission policies become more stringent and the use of high‐efficiency vehicles and alternative modes increases, vehicle miles traveled would be significantly reduced and transportation emissions with them.
Agricultural land conversion would be lower in this story line as a result of less urban expansion and the use of farming easements and other incentives to maintain land in farming. Though long‐term temperatures may be lower than in the A2 story line, average temperatures in 2050 do not differ . Consistent with AB 32, voluntary actions in agriculture would place more emphasis on increasing carbon sequestration and decreasing N2O emissions through multiple crops per year, more ecologically intensive practices, reduction of fertilizer use, and efforts to capture methane emissions from livestock. Moreover, there would be greater societal investment in preparing ahead for climate change adaptation options, such as crop breeding, pest management, and resilience to intermittent droughts. Under B1, Yolo County experiences the benefits of slower population growth and improved urban land use practices, resulting in preservation of agricultural land and reduced GHG emissions.To the two IPCC‐based story lines, we add a third scenario with more stringent GHG emissions regulation than AB 32. Under our AB32+ story line, Yolo County experiences slower population growth reaching only 235,000 in 2050, which would have to occur through policies or voluntary actions that affect family planning and migration . In this story line, moderate economic growth focuses on value‐added production economic viability of the local rural sector, and support for ecosystem services generated by closer alignment between the rural and urban sectors . A less resource‐intensive lifestyle would dominate, coupled with an increase in the quality of life through an increase in ecosystem services in both sectors. Priorities would be placed on both regulating services and cultural services . The urban boundary remains at the current extent through strict land use planning policies and development emphasizing efficient use of land, mixed use, intense infill, increased densities,hydroponic gutter and growth in the urban core. More compact development patterns and the promotion of local development and payment for ecosystem services, coupled with many alternative modes of transportation and increased use of zero emission vehicles, would result in a reduction of vehicle miles traveled and GHG emissions from transportation. Although long‐term temperatures may be lowest under this scenario, 2050 temperatures are essentially the same as in the other story lines. In order to both mitigate and adapt to the changing climate, agricultural producers would make major changes in management practices, focusing on ecological intensification rather than on non‐renewable inputs. This would require substantial societal investment in development of new renewable technologies and for diversification of cropping systems to fit site‐specific situations. Practices such as farm scaping and revegetation of riparian buffer zones to mitigate and reduce GHG emissions would also be promoted for their co‐benefits, such as improved water quality .
Markets for products may become more locally based, and efforts would be made to reduce GHG emissions from processing and transport of agricultural products. Overall emissions would be the lowest under AB32+ with a reduction from urban areas due to denser, more balanced land development, less resource‐intensive lifestyles, and improved transportation options. Changes in crop choice and management practices would likewise reduce GHG emissions from agriculture. In addition to modeling these three scenarios using UPlan, we modeled additional versions of A2 and AB32+ in which population was held constant at the B1 level. This step allows us a more analogous comparison of the three story lines.After using UPlan to produce urban growth footprints for the above scenarios, we calculated two main categories of GHG emissions for the new urbanization produced by each. These calculations are very approximate, but help to give a sense of the magnitude of variations that can result from different policy approaches. One category of GHG emissions was from transportation. Household travel surveys done by SACOG show that household vehicle miles travelled vary by a factor of six between households in low‐density per acre and high‐density locations . Some of this difference may be due to household size and composition, but much is likely due to proximity to jobs, shopping, schools, and alternative transportation modes. In addition, many other policy steps in the lower GHG emissions scenarios are likely to reduce driving in the 2050 time frame. These other factors include rising gas or carbon taxes; improved balance of jobs, housing, and shopping within communities; improved bicycle, pedestrian, and public transit options; and other economic incentives such as higher parking charges and tolls. Transportation emissions are also of course dependent on the fuel efficiency of motor vehicles. Average fuel efficiency of American vehicles remained more‐or‐less unchanged from the mid‐ 1980s through 2010, and so for purposes of illustration, this was assumed in the A2 scenario until 2050. In the B1 scenario, we assumed modest efficiency increases of 2 percent a year , and for the AB32+ scenario we assumed improvements of 4 percent a year . Rather than continually improve conventional gasoline engines, these scenarios would most likely see increasing percentages of the motor vehicle fleet converting to hybrid or all‐electric propulsion, with an increasing proportion of the electricity produced by renewable sources.Household energy use was a second category of calculated GHG emissions. In Yolo County domestic energy comes almost entirely from electricity or natural gas, as oil heating is rare in California and use of wood stoves is also low and increasingly discouraged due to local air pollution concerns. Here again we can expect substantial differences in GHG emissions between infill urbanization and new residential development on agricultural land, due to larger unit sizes and a much higher percentage of stand‐alone single family homes in the former case. To calculate household energy use for the three scenarios, we used data from the 2009 California Residential Appliance Saturation Study , a collaboration of the state’s five largest utility companies that surveyed detailed consumption habits of nearly 26,000 households. This study breaks households down by climate zone, and compares energy consumption for single‐family homes, town homes, small multifamily buildings, large multifamily buildings, and mobile homes by California Energy Commission climate zone. Both electricity and gas use for the middle three categories were approximately half that of single family homes, probably in large part because average unit sizes were smaller, and perhaps also because shared‐wall construction tends to be more energy efficient than stand‐alone single‐ family homes.