A Development Framework for Two - Dimensional Large Basin Operational Hydrologic Models

Large-scale operational hydrologic models are essential tools in support of multiple water resource applications such as flood control, navigation, irrigation, and habitat management, etc., at the regional or continental scales. These models, unlike micro scale watershed models, are defined over large areas (>10 km) and long time scales (typically for use over monthly and annual or longer time scales at a daily interval). Often constrained by limited data availability, computational requirements, and model application costs over larger areas, large-scale models must have few parameters, use easily accessible meteorologic and hydrologic databases, and be user-friendly. Horberger and Boyer (1995) found that better representation of spatial and temporal variability and appropriate parameterization of hydrologic processes have become critical in recent years. They reviewed recent advances in watershed modeling pertinent to use of Geographic Information Systems (GIS), remotely sensed data, and environmental tracers for micro scale modeling. This paper addresses the needs and challenges of large-scale operational hydrologic models through the development of a modeling framework. It focuses on advances in parameterization of the infiltration and evapotranspiration processes and on the representation of large-scale spatial variability. It first reviews recent developments in hydrologic modeling and then proposes a developmental framework for integrating remote sensing, multiple databases, and emerging hydrologic algorithms in twodimensional large-scale runoff modeling. Finally an application of the proposed framework is made for the Laurentian Great Lakes by spatially extending the lumped-parameter large basin runoff model (LBRM) developed at the Great Lakes Environmental Research Laboratory (GLERL).