SWAP

General Description

The Statewide Agricultural Production Model (SWAP) is a multi-region, multi-input and output model of agricultural production, which self-calibrates using the method of Positive Mathematical Programming (PMP). PMP simulates the effects of policy changes on cropping patterns at the extensive and intensive margins by integrating observed data into model calibration. The model chooses the optimal amounts of land, water, labor, and other input use subject to these constraints and definitions. Profit is revenue minus costs, where revenue is price x yield per acre times total acres.
http://swap.ucdavis.edu

Model Domain

Agricultural economics of California

Developer

Howitt, Medellin-Azuara, MacEwan, Lund. Originally at UC Davis

Hardware computing requirements

Not specified

Code language

GAMS

Original application

Developed as an agricultural economic component of CALVIN model of California water systems. http://calvin.ucdavis.edu

Public/proprietary and cost

For research-related applications available through UC Davis Center for Watershed Sciences or UC Merced (public).
Business application through ERA Economics (proprietary).

Physically or empirically based

Empirical

Mathematical methods used

Based on Positive Mathematical Programming (Howitt 1995) calibrated to a base datasets on crop production input use, prices, costs and yields. Constant Elasticity of Substitution (CES) production functions are generated for every crop in every region.

Input data requirements

(brackets include example datasets)

• Land Use
• Crop prices (county ag commissioners)
• Crop Yields (UCCE crop budgets)
• Interest rates (UCCE crop budgets)
• Land Use costs (UCCE crop budgets)
• Supply costs (UCCE crop budgets)
• Labor costs (UCCE crop budgets)
• Surface water costs (USBR/DWR/water districts)
• Irrigation water (DWR)
• Available water (CVPM/DWR/USBR/water district)
• Crop Pricy Supply Elasticities (Russo et al. 2008)

Outputs

Outputs for 27 base regions (21 CVPM regions) in the Central Valley for 20 crop groups.

• Allocation of acreage per crop type
• Economic value

Pre-processing and post-processing tools

None specified

Representation of uncertainty

None specified

Prevalence

Used in policy analysis by both academic and state agencies

Ease of use for public entities

Requires knowledge of GAMS software and access to program through UC Davis. Alternatively, ERA Economics provides paid access to model interface and modelling services for SWAP.

Ease of obtaining information and availability of technical support

Through UC Davis Center for Watershed Sciences for research purposes.
ERA Economics provides services to run scenarios. Freely available manuals or information on technical model runs is not currently available.

Source code availability

Not freely available

Status of model development

Model Version 6.1 is available for research and other application through UC Davis Center for Watershed Sciences. Version RTS (decreasing returns to scale) available through ERA economics.

Challenges for integration

Currently integrated with CALVIN, IMPLAN, and CALSIM II models. Detailed inputs. Constrained crop groups may not map well to other models. New crop groups or updated crop valuation requires calibration for economics as well as land use. Model is data driven, can be run without recoding by changing input data. Model output scale may not match with other models.