Angra dos Reis, Brazil, September 2000

The primary goal of MOPEX (Model Parameter Estimation Experiment) is to develop techniques for improved a priori estimation of the parameters used in land surface parameterization schemes of atmospheric models and in hydrological models. The major effort to achieve this goal is to assemble a large number of high quality historical hydro meteorological and river basin characteristics data sets for a wide range of Intermediate Scale Area (ISA) river basins (500 - 10 000 km²) throughout the world. The MOPEX project began in 1997 with funding by the GCIP project. MOPEX Phase II has been similarly funded for the three years from 2000 to 2002.

The primary focus of the project to date has been to create an initial data base primarily using data from the United States. Some 2000 U.S. basins with substantially unmodified streamflow were examined. The majority of these were too small to qualify as an ISA basin or were found to have insufficient precipitation data to adequately represent this key forcing data. To date around 70 basins have been selected in the Mississippi River basin for which daily average basin precipitation and discharge data have been computed. Currently hourly precipitation data are being prepared these. It is planned to have average hourly precipitation and daily streamflow data available for around 200 ISA basins covering the entire U.S.

The purpose of MOPEX Phase II is to collect additional data from the U.S. and from other countries as well. The additional U.S. data will include both additional basins and additional data for the existing basins, including hourly gage-based precipitation data for all U.S. basins and distributed, hourly, gage + radar multisensor data for selected basins. Data from other countries would include basins in North and South America, Europe and Australasia. Data from Asia and Africa also will be obtained and initial steps have been taken to do this, but the basic data collection strategy being used in MOPEX is to seek the most readily available and highest quality data first. It is hoped that these data will be used by the scientific community to analyze model parameters for selected MOPEX basins and that the results of these analyses will be discussed during a number of workshops and symposia that would be organized by MOPEX. The first MOPEX related symposium, "S5 SVAT and Precipitation Process Modelling at Large Catchment (> 1000 km²), Regional and Continental Scales" - "S5.2 Parameter Estimation of Large-Scale Hydrological Models" will be held as part of the 6^th Scientific Assembly of the IAHS in Maastricht in July, 2001. A stand alone MOPEX workshop is being planned for the middle of 2002.

MOPEX Objectives

Key Scientific Issues

1. How do we develop improved a priori parameter estimation procedures that can be used for large scale land surface process modelling.
2. How do we demonstrate the transferability of land surface models?
3. What type of hydro meteorological data and land/hydrology characteristics data are needed for developing parameter estimation procedures?

 MOPEX Strategy

The MOPEX science strategy is illustrated in Figure1. The first step of the strategy is to develop the necessary data sets The strategy is then to use these data to study each model that would participate in MOPEX using 3 parallel paths illustrated in Figure1. The first path is to make

control runs with model parameters estimated using existing a priori parameter estimation techniques. The second path is to make model runs using calibrated or tuned values of selected model parameters. The third path is to make model runs using new a priori parameters estimated from techniques developed by analysis of possible relationships between basin climate, soils, vegetation and topographic characteristics and calibrated model parameters.

Achievement of the MOPEX goal is then established in two steps. The first is to measure how much of the calibrated model improvement is obtained when the model is operated using new a priori parameters. The second step is to demonstrate that new a priori techniques produce better model results than existing a priori techniques for independent basins not used to develop the new a priori techniques.

MOPEX Contributions to GHP

The GEWEX Hydrometeorology Panel (GHP) endorsed the concept of an international Model Parameter Estimation Project (MOPEX) at its Toronto meeting, August 1996. MOPEX subsequently was adopted as projects of the IAHS/WMO Working Group for GEWEX in November 1996 and of the WMO Commission for Hydrology at its 10^th Session in December 1996. Future MOPEX activities should contribute to several of the objectives of the Coordinated Enhanced Observing Period (CEOP-I) project of the GHP. First, MOPEX data sets in the U.S. can be used to develop improved a priori parameter estimates for models used in CEOP land surface process and modelling studies. Second, MOPEX data sets outside the US can be used to demonstrate the transferability of the results from CEOP land surface process and modelling studies. Third, MOPEX data sets are an important source of climate data that are needed to demonstrate improved skills in climate predictions and in water resources applications.

MOPEX Actions

1. Develop hourly precipitation data sets and additional basin characteristics data for the U.S. basins for which daily precipitation and streamflow data were already compiled.
2. Develop data sets for additional U.S. ISA basins.
3. Develop data sets for additional international ISA basins.
4. Provide all data to the scientific community via the Internet.
5. Develop a priori parameter estimation schemes using the above data sets for the NOAH model (U.S. Weather Service National Center for Environmental Prediction land surface scheme) and the Sacramento soil moisture accounting model (used by U.S. River Forecast Centers).
6. Identify a few basins for detailed testing and evaluation in the GHP CSEs where high quality data sets will be produced during enhanced observing periods (e.g. from GCIP - ARM/CART area, Little Washita River and Des Moines River; and one in each of the MAGS, BALTEX, GAME -Tropics, GAME-Subtropic, GAME-Tibetan Plateau and GAME-Siberian Tundra experiments). These data sets include surface flux measurements, soil moisture and frozen ground and snow measurements (in cold regions).
7. Conduct international MOPEX symposia and workshops to assess progress and provide direction to the MOPEX project and to individual scientists working on the parameter estimation problem.
8. Collaborate with the GEWEX Project for the Intercomparison of Land-Surface Parameterization Schemes (PILPS) to conduct detailed studies using parameters estimated with the assistance of the MOPEX data sets.

Updates

Additional information will be provided on the aforementioned website as the project progresses.

Contacts

John Schaake (), Qingyun Duan () and Alan Hall () NOAA/NWS Office of Hydrology