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The amount of water used for irrigation varies as a function of the local weather conditions and soil type, crop and cultivar selection, crop management, and irrigation strategies, including the timing and amount of irrigation applications. Among these factors, weather conditions and the soilwater holding characteristics are often the most important factors that define the spatial variability of irrigation in a specific region. In Georgia, the amount of water used by agriculture for irrigation is largely unknown because of the lack of reporting requirements. Recent droughts and a water dispute with the neighboring states, including Alabama and Florida, highlighted the need for an accurate estimate of water use by agriculture. The goal of this study was to characterize the spatial variability of the monthly irrigation water use for cotton in Georgia using the Cropping System Model (CSM) of the Decision Support System for Agrotechnology Transfer (DSSAT) Version 4.0. Farmers' monthly irrigation applications for cotton during the 2002 growing season were obtained from selected sites of the Agricultural Water Pumping program. We selected farmers fields that were located within 15 km from the nearest weather station of the Georgia Automated Environmental Monitoring Network or the Cooperative Observer Program (COOP) network of the National Weather Service. We then compared the spatial and temporal distribution of irrigation amounts predicted by the CSM model with the amount of water that the farmers actually applied. The most successful model for spatial estimation of monthly total irrigation was the Spherical model, followed by the Exponential model. The smaller number of sample sites in certain parts of the study area had a significant impact on spatial estimates of monthly total irrigation. This study demonstrated the potential of using a crop model combined with geostatistical techniques for estimation of regional water use.