SWAP

General Description

The Statewide Agricultural Production Model (SWAP) is programming optimization model of agricultural production and water use, which self-calibrates to a base input dataset using Positive Mathematical Programming (PMP). SWAP predicts the effects of land, water, economics and/or policy scenarios, on cropping patterns with respect to baseline calibration conditions. The model chooses  amount of land, water, labor, and other input use in agricultural production such that net returns to land and management are maximized within resource constraints or economic parameters including production costs, crop yields and prices.  The model website is at: http://swap.ucdavis.edu

Model Domain

Agricultural economics of crops in California

Developer

Howitt, Medellin-Azuara, MacEwan, and Lund. Originally at the University of California at Davis (UC Davis)

Hardware computing requirements

Runs in MS windows environment.

Code language

Generalized Algebraic Modeling System (GAMS)

Original application

Developed as an ancillary model to the CALVIN model of California water supply system ( http://calvin.ucdavis.edu ), providing economic value of water in agriculture. 

Public/proprietary and cost

For research-related applications available through UC Davis Center for Watershed Sciences or UC Merced Water Systems Management Group

Business applications through ERA Economics (proprietary).

Physically or empirically based

Empirical calibrated to predetermined baseline agricultural land and water use conditions.

Mathematical methods used

Based on Positive Mathematical Programming (Howitt 1995, Howitt et al. 2012) 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

Input data requirements include (values in parentheses refer to source datasets, these can vary):

• Land use (USDA-NASS County Agricultural Commissioner's Reports, and DWR).
• Crop prices (USDA-NASS County Agricultural Commissioner's Reports)
• Crop yields (USDA-NASS County Agricultural Commissioner's Reports)
• Land rental costs (UCCE crop budgets)
• Supply costs (UCCE crop budgets)
• Labor costs (UCCE crop budgets)
• Surface water costs (USBR/DWR/water districts)
• Applied irrigation water (DWR)
• Available water (CVPM/DWR/USBR/water district)
• Crop Price Supply Elasticities (Russo et al. 2008)

Outputs

Cropping patterns for 27 regions (within 21 CVPM regions) in the Central Valley, and irrigated agriculture in selected coastal and inland areas (Medellin-Azuara et al. 2015) for 20 crop groups following DWR and CalSIMETAW classification.

• Allocation of acreage per crop type. Input use: land, water, labor and other agricultural production supplies.
• Economic value of production

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 code through the University of California. Alternatively, ERA Economics provides paid access to model interface and modelling services for SWAP.

Ease of obtaining information and availability of technical support

Selected modeling applications can be obtained through the University of California, Center for Watershed Sciences or the Water Systems Management group at UC Merced (Medellin-Azuara). 

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 collaborative research and other application through UC Davis Center for Watershed Sciences. Version RTS (decreasing returns to scale) is available through ERA Economics. Model continues updating and development as new land, water, and economic information is available. 

Challenges for integration

Currently integrated with CALVIN, C2VSim and CALSIM II models in various applications, but running simultaneously within other platforms can be a challenge due to the GAMS native platform. Nevertheless, models outputs such as cropping patterns and economic value can be easily cascaded into other models (e.g. REMI, IMPLAN). Model spatial scale is easily changeable, yet the native temporal scale is annual cropping decisions. Substantial changes with respect to the baseline input use conditions may require a model recalibration.