The present paper discusses a coupled gridded crop modeling and hydrologic modeling system that can examine the benefits of irrigation and costs of irrigation and the coincident impact of the irrigation water withdrawals on surface water hydrology. The system is applied to the Southeastern U.S. The system tools to be discussed include a gridded version (GriDSSAT) of the crop modeling system DSSAT. The irrigation demand from GriDSSAT is coupled to a regional hydrologic model (WaSSI). GriDSSAT and WaSSI are coupled through the USDA NASS CropScape data to provide crop acreages in each watershed. The crop model provides the dynamic irrigation demand which is a function of the weather. The hydrologic model responds to the weather and includes all other anthropogenic competing uses of water. Examples of the system include an analysis of the hydrologic impact of future expansion of irrigation and the real-time impact of short-term drought. The GriDSSAT model presented in this paper was developed with the Decision Support System for Agrotechnology (DSSAT), a software application program that comprises crop simulation models for over 28 crops and is supported by data base management programs for soil, weather, and crop management and experimental data, and by utilities and application programs. The latest version can be obtained free at: http://www.dssat.net. The WaSSI model is an integrated, process-based model that was originally developed by the U.S. Forest Service. More information is available at: http://www.forestthreats.org/tools/WaSSI. 
An integrated crop and hydrologic modeling system to estimate hydrologic impacts of crop irrigation demands