DAP (Delta Agricultural Production Model)

General Description	Based on SWAP, DAP is used to model agricultural land and water use and economic performance but unlike SWAP, DAP disaggregates by agricultural islands and includes the effects of salinity in the water supply on crop yields. http://swap.ucdavis.edu
Model Domain	Agricultural economics of the Delta
Developer	Howitt and Medellin-Azuara (UC Davis) based on SWAP model
Hardware computing requirements	Not specified
Code language	GAMS
Original application	Developed for use in PPIC report "Envisioning Futures for the Sacramento-San Joaquin Delta" (Lund et al., 2007).
Public/proprietary and cost	Based on SWAP model, modifications to algorithms available in Lund et al. (2007), runs on GAMS.
Physically or empirically based	Empirical
Mathematical methods used	Expansion of SWAP methods, which use positive mathematical programming (PMP) (Howitt, 1995). Salinity response in DAP is based on the Van Genuchten & Hoffman (1985) inverse sigmoid yield response function.
Input data requirements	(brackets include example datasets) Salinity data (monitoring station data from DWR) Land Use Crop prices Crop Yields Interest rates Land costs Supply costs Labor costs Surface water costs (USBR/DWR/water districts) Irrigation water (DWR) Available water (CVPM/DWR/USBR/water district) Elasticities (Russo et al. 2008)
Outputs	Outputs for 71 regions in the Sacramento San Joaquin Delta 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, private consultants, and state agencies
Ease of use for public entities	Requires knowledge of GAMS software, economic optimization and production economics theory, and access to program through UC Davis in addition to DAP algorithms.
Ease of obtaining information and availability of technical support	Manuals or information on technical model beyond policy publications runs is not currently available.
Source code availability	None
Status of model development	Several iterations use different disaggregation units, or additional areas of the Central Valley.
Challenges for integration	Similar to those of SWAP, however, DAP is also disaggregated into 71 smaller regions of the Delta. Model output scale map not match outputs of other models.

References:
Howitt, R. (1995). A calibration method for agricultural economic production models. Journal of Agricultural Economics, 46(2), 147–159. https://doi.org/10.1111/j.1477-9552.1995.tb00762.x
Howitt, R. E., Macewan, D., Medellín-Azuara, J., & Lund, J. R. (2010). Economic Modeling of Agriculture and Water in California using the Statewide Agricultural Production Model. California Water Plan Update 2009, 4, 1–25.
Lund, J., Hanak, E., Fleenor, W., Howitt, R., Mount, J., & Moyle, P. (2007). Envisioning Futures for the Sacramento-San Joaquin Delta. Public Policy Institute of California. San Francisco, CA. https://doi.org/10.1007/s13398-014-0173-7.2
Medellin-Azuara, J. M., Howitt, R. E., Lund, J. R., & Fleenor, W. E. (2008). The Economic Effects on Agriculture of Water Export Salinity South of the Delta: Technical Appendix I. Comparing Futures for the Sacramento-San Joaquin Delta.
Medellín-Azuara, J., Hanak, E., Howitt, R., Lund, J., Ferrell, M., Kramer, K., … Stryjewski, E. (2012). Transitions for the Delta Economy Appendix A: Estimates of Acreage and Land Use. Public Policy Institute of California. San Francisco, CA.
Medellín–Azuara, J., Howitt, R. E., Hanak, E., Lund, J. R., & Fleenor, W. (2014). Agricultural Losses from Salinity in California's Sacramento-San Joaquin Delta. San Francisco Estuary and Watershed Science, 12(1), 1–16.
Van Genuchten, M., and G. Hoffman. 1985. "Analysis of Crop Salt Tolerance Data." In Soil Salinity under Irrigation, Processes and Management, ed. Shainberg, I., and J. Shalhevet (Berlin: Springer: Ecological Studies), 258–71.