Physically based, field scale agro-hydrological models provide a robust way to understand the cause-effect relationships of the interrelated variables in the soil-plant-atmosphere system. One weakness of field scale models is their inability to account for the heterogeneity in a system (i.e. a hydrological domain) at the regional level. This is important to overcome because of its broad implications to water management studies. In this book, a methodology was developed to address this problem using Remote Sensing Ð Simulation Modeling approach.