We provide herein a water and energy budget synthesis (WEBS) for the Global Energy and Water Cycle Experiment’s (GEWEX’s) Continental Scale International Project (GCIP) over the Mississippi River Basin from observations and models for the period 1996-1999. The synthesis includes a general description of the Basin climate, physiographic characteristics, a brief description of available observations, types of models used for GCIP investigations, and a comparison of water and energy variables and budgets from models and observations.

Observations cannot adequately close budgets since too many fundamental observations are missing. Models, especially analysis models are required for many individual processes that are not really measured in any meaningful way on a continental scale. For example, soil moisture and evaporation are measured at only a few sites, although there are intensive efforts to develop satellite-derived products. High-resolution atmospheric moisture and dry static energy convergence cannot easily be derived from radiosonde observations. Models that properly represent complicated interactions may ultimately provide better overall descriptions of the budgets than any attempt to grid observations of a single variable from only knowledge of only the observations. Models will also be required for predictions.

Therefore, as part of the general synthesis, the purpose of this talk is to compare different classes of models with available observations. We compare a global general circulation model with a regional climate model along with global and regional analyses, a macroscale hydrologic model and observations. There does appear to be a clear advantage to using a regional analysis over a global analysis or a regional simulation over a global simulation to describe the budgets. There also appears to be some advantage to using a macroscale hydrologic model for at least the surface water budgets although the surface energy budgets may still be better simulated by the atmospheric analyses.