How might the urbanization of agricultural land affect greenhouse gas emissions in Yolo County?

Yolo County has been relatively successful at protecting agricultural land from conversion through land preservation programs, incentives for farmers, and land use policies which make it difficult to develop land zoned for agriculture. But by 2050 the county's population may reach 394,000 [4] up from 199,407 in 2010, resulting in pressure to expand the current urban footprint. Urbanization onto agricultural land raises two important issues: a loss of agriculturally productive land that provides food for a growing population, and an increase in greenhouse gas (GHG) emissions from decentralized urbanization. Yet, legislation such as AB32 and SB375 aim to reduce emissions 20% below 1990 levels by 2020 [1]. Thus we need to better understand the interrelationships between urbanization, agriculture, and GHG emissions.

City of Winters

Figure 1. City of Winters in Yolo County is surrounded by agriculture and demonstrates relatively compact growth.

What is UPlan and how can it help?

UPlan is a land use allocation model developed by the Information Center for the Environment at the University of California Davis [7]. More specifically, it is GIS based software suitable for fast, broad-brush urbanization modeling using multiple development scenarios. UPlan has already been used as an urban planning tool by more than 20 counties in California, including a group of rural counties in the San Joaquin Valley [6]. Here we review a recent study conducted by UC Davis using UPlan to examine several hypothetical "storylines" for future urbanization and GHG mitigation in Yolo County, CA (by Wheeler, Tomuta and Jackson in Jackson et al. in review) [3].

What urban growth storylines were used in the Yolo County study?

The study examined the following three storylines between 2010-2050:

A2- Regional Enterprise

The A2 Storyline is a near continuation of current demographic, economic, technological, and environmental trends but reflects some improvements in response to current climate change initiatives and legislation.

Population growth remains high, in line with the A2 emissions projections made by the Intergovernmental Panel on Climate Change [2], thereby doubling the current county population from 197,530 (as of 2009) to 394,000

Continued economic growth and technological innovation lead to a 50% increase in the area of urbanized land

Though some focus remains on generating a greater mix of land uses, higher densities, and more infill, substantial agricultural land is nevertheless lost to urban development

Fossil fuel related-emissions increase as a result of more drivers and larger urban areas as well as the predominance of automobiles for transportation

B1- Global Sustainability

B1 is a relatively "green" scenario in which communities become more conscious of environmental problems and climate change, and sustainable development efforts are implemented.

Population growth slows, reaching approximately 335,000 by 2050

AB 32 enables the reduction of GHG emissions to 1990 levels by 2020 through emission limits and reduction measures, and mandatory reporting

Technological innovation remains robust in the Sacramento region, with an emphasis on small-scale, green technologies

Vehicle miles traveled and transportation-related emissions are significantly reduced as transportation and emission policies become more stringent and the use of high efficiency vehicles and alternative modes become more prevalent

Agricultural land conversion is reduced from the Regional Enterprise (A2) scenario above

AB32 Plus- Precautionary Change

Overall emissions are lowest under AB32 Plus due to a more dense, in-fill oriented land development, less resource intensive lifestyles, and improved transportation options.

Population growth slows even further, reaching only 235,000 from the present population of approximately 200,000

Moderate economic growth focuses on additional value from agricultural products via processing or labeling, small industries, and the rural-agricultural sector

The urban boundary remains nearly unchanged due to land use policies that emphasize efficient and mixed land use, intense infill, increased densities, and growth within the urban core

Alternative modes of transportation, including increased use of zero emission vehicles, result in a reduction of vehicle miles traveled and emissions from transportation

Agricultural producers adopt less GHG intensive management practices, focusing on multicropping, agrobiodiversity-based approaches, and efforts to capture methane emissions from livestock

How much new development is predicted to occur by 2050 in Yolo County?

New development by land use type

Table 1. Summary of new development by land use type under each storyline.

The storylines affect the amount and type of land uses and whether "urban sprawl" will occur. Under A2 (our current trajectory), for example, low-density residential, low-density commercial, and very low-density residential take up 9,081 2,687, and 1,441 acres respectively, and amount to nearly 90 percent of all new development.

Urban growth in Yolo County

Figure 2. Urban Growth in Yolo County, 2010-2050, A2 Scenario, Detail of Cities

In the B1 storyline, medium-density residential development takes up a larger percentage of newly developed land area, while in AB32 Plus, most development is either medium or high-density residential. One of the most striking findings is just how little land is required to house future populations at these higher densities. The B1 and AB32 Plus scenarios require 44 and 7 percent of the land of the A2 scenario respectively. Even holding population constant at B1 levels, the B1 and AB32 scenarios use 63 and 38 percent of the land of the A2 scenario, and they confine most or all of the growth within existing urban areas.

How is agricultural land likely to be impacted by future urbanization?

A map with the county's crop distribution was overlaid on to maps with UPlan results to determine crop acreage lost to urban growth under each storyline. Under A2, 72 percent of development takes place on agricultural land. Under B1 development on agricultural land makes up 52 percent, and under AB32 Plus only two percent. Crop and rangeland acreage lost to development varies greatly among the three storylines, ranging from 10,562 in A2 (16.5 square miles) to 3,363 in B1 (5.3 square miles) to 23 in AB32 Plus (0.04 square miles). These results reflect the lower total population growth and stricter urbanization policies in the B1 and AB32 Plus storylines.

Total acres under development

Table 2. Total acres of development on agricultural land under each storyline by 2050 in Yolo County.

How does this new development contribute to transportation and residential energy related GHG emissions?

Not surprisingly, transportation emissions related to new development vary greatly across the three storylines. Under the A2 scenario, transportation-related emissions are approximately 789,229 metric tons of GHG equivalent annually. The B1 scenario produces 254,243 metric tons of emissions, and the AB32 scenario produces just 63,244 metric tons. Even holding population, vehicle efficiency, and household size constant, the GHG emissions between the three scenarios are profoundly different.

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.

Residential transportation greenhouse gas emissions

Table 3. Residential transportation greenhouse gas emissions by storyline.

Residential energy-related GHG emissions also show large differences among the three scenarios, due to the lower energy usage of multifamily units compared with single family homes, as well as other assumptions about efficiency improvements and electric portfolio composition between the scenarios. Again, the storylines show just how large a reduction in emissions can be achieved through a combination of initiatives. Annual electricity-related emissions from residential development within the 2010-2050 time period range from 132,104 metric tons in the A2 scenario to 60,548 in the B1 scenario and just 11,536 metric tons in the AB32 Plus scenario. Holding population constant across the three scenarios diminishes differences only slightly.

Overall, the AB32 Plus scenario produces by far the lowest amount of emissions from residential development and also results in lower conversion of agricultural land, and management to reduce agricultural GHG emissions and support carbon sinks via restoration. The B1 scenario also produces substantial greenhouse gas savings. Emissions in this scenario are about 36 percent and 50 percent of those in A2 under the two different population levels, demonstrating that the preservation of agricultural land is essential if the county is to reduce its GHG emissions.

Overall residential GHG emissions

Table 4. Overall (transportation plus residential) GHG emissions from new residential development (2010-2050)

Where can I find more information on UPlan, GHG mitigation, and local land use policies?

UPlan - Model website from the Information Center for the Environment (UC Davis)
Yolo County General Plan - Explains county’s goals by 2030
Yolo County Climate Action Plan - Yolo County Planning Department website


[1]California Air Resource Board. 2008. Climate Change Scoping Plan.
[2]Intergovernmental Panel on Climate Change. 2000. IPCC Special Report Emissions Scenarios.
[3]Jackson, L.E., V.R. Haden, A. Hollander, H. Lee, M. Lubell, V. Mehta, T. O'Geen, M. Niles, J. Perlman, D. Purkey, W. Salas, D. Sumner, M. Tomuta, M. Dempsey, and S. Wheeler. Agricultural Mitigation and Adaptation to Climate Change in Yolo County, CA. In preparation for California Climate Change Center Report.
[4]Johnson, H. 2008. California Energy Commission Scenarios Analysis Project. Public Policy Institute of California.
[5]Johnston, R.A., N. Roth, and J. Bjorkman. 2009. Adapting Travel Models and Urban Models to Forecast Greenhouse Gases in California. Transportation Research Record Board, 2133, 23-32.
[6]Richter, K. 2009. Sharpening the focus of Yolo County land use policy. University of California Agricultural Issues Center.
[7]Walker, W. Thomas, S. Gao, and R.A. Johnston. 2007. UPlan: Geographic Information System as Framework for Integrated Land Use Planning Model. Transportation Research Record, No. 1994, 117-127.