Model Parameter Estimation Experiment (MOPEX) is an international project aimed to develop enhanced techniques for the a priori estimation of parameters in hydrologic models and in land surface parameterization schemes of atmospheric models. MOPEX science strategy involves three major steps: data preparation, a priori parameter estimation methodology development, and demonstration of parameter transferability. A comprehensive MOPEX database has been developed that contains historical hydrometeorological data and land surface characteristics data for many hydrologic basins in the United States and in other countries. This database is continuing to be expanded to include more basins in all parts of the world. A number of international MOPEX workshops have been convened to bring together interested hydrologists and land surface modelers from all over world to exchange knowledge and experience in developing a priori parameter estimation techniques. This paper describes the results from the second and third MOPEX workshops. The specific objective of those workshops is to examine the state of a priori parameter estimation techniques and how they can be potentially improved with observations from well-monitored hydrologic basins. Participants of these MOPEX workshops were given data for 12 basins in the Southeastern United States and were asked to carry out a series of numerical experiments using a priori parameters as well as calibrated parameters developed for their respective hydrologic models. Eight different models have carried all out the required numerical experiments and the results from those models have been assembled for analysis in this paper. This paper presents an overview of the MOPEX experiment design. The experimental results are analyzed and the important lessons from the two workshops are discussed. Finally, a discussion of further work and future strategy is given
