SWAPDefault

	Principal Investigator Richard E. Howitt, Professor and Chair Agricultural and Resource Economics University of California, Davis howitt@primal.ucdavis.edu
Reasearch Collaborators
Jay R. Lund, Ray B. Krone Professor Department of Civil and Environmental Engineering Director, Center for Watershed Sciences University of California, Davis jrlund@ucdavis.edu	Josue Medellin-Azuara, Research Scientist Department of Civil and Environmental Engineering, Center for Watershed Sciences University of California, Davis jmedellin@ucdavis.edu	Duncan MacEwan, Ph.D. Student Geography Graduate Group University of California, Davis macewan@primal.ucdavis.edu
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The Statewide Agricultural Production Model (SWAP) was developed by Howitt and collaborators in 2001 and continues to be improved upon. The original use for this model was to provide the economic scarcity cost of water for agriculture to CALVIN (Jenkins et al. 2001), a statewide economic engineering optimization model for water management in California. More recently, SWAP has been used to estimate economic losses due to salinity in the Central Valley (Howitt et al. 2008), economic losses to agriculture in the San Joaquin Delta (Appendix to Lund et al. 2007) and economic losses for agriculture and confined animal operations in California’s Central Valley (Appendix to Lund et al. 2008).

SWAP is an optimization model for major crops and agricultural regions in California and uses Positive Mathematical Programming (or PMP, after Howitt 1995).
Implicit in this model is the assumption that farmers optimize their production input use to maximize their own profit.

To generate more accurate results, this version of SWAP contains several innovations including:

Endogenous crop group prices for the year 2050
Geo-referenced land use information
Updated price and production cost information
Use of an exponential constant elasticity PMP cost function
Updated information on yield reduction due to climate warming

PMP is a deductive approach to evaluating the effects of policy changes on cropping patterns at the extensive and intensive margins. SWAP is a three-step, self-calibrating programming model that assumes that farmers behave in a profit-maximizing fashion. In the first step, a linear program for profit maximization is solved. In addition to the traditional resource and non-negativity constraints, a set of calibration constraints is added to restrict land use to observed values. In the second step, the optimization first order conditions are used to derive the parameters for an exponential cost function and a non-linear Constant Elasticity of Substitution (CES) production function. The third and last step incorporates the parameterized functions from step two into a non-linear profit maximization program, with constraints on resource use.

SWAP Model Overview

SWAP Water Markets Schematic

	Coverage of SWAP includes: The CVPM regions in the Central Valley Initially 21 regions Reconfigured to 26 regions Agriculture in the Central and South California coasts including: Salinas Ventura Santa Ana San Diego Agriculture in the Colorado River Region Coachella Palo Verde Imperial Valley
Applications of SWAP Employment Impacts of California 2009 water drought Report Appendices Salinity in the Central Valley SWAP Lite (upcomming) SWAP Applications in Mexico Economic value of agricultural water shortages (CALVIN-SWAP 2001). Economic Cost of Salinity in the San Joaquin Delta