Validating the Estimates of Grobal Water Balance by Global River Runoff Dataset

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As one effort to estimate the global soil moisture distribution, the Global Soil Wetness Project (GSWP) was conceived. A gridded 1 degree by 1 degree global river channel network, named Total Runoff Integrating Pathways (TRIP) is used to calculate mean runoff estimated by the LSMs for drainage areas upstream of 250 operational gauging stations. Runoff observations from these stations in 150 major river basins of the world have been collected for years in 1987 and 1988, and were compared with the LSM products. It was found that LSMs estimated annual runoff fairly well with a relative root mean, square error of 40 [%] for drainage areas with a fairly high density of raingauge observations (30/lmil. sq. km) which was used to prepare the forcing precipitation. The error corresponds to approximately 18 [%] of annual evapotranspiration. LSMs are also found to have a tendency to underestimate the annual runoff. It may be caused by underestimation of raingauges under strong wind conditions, especially for snow, as all of the LSMs underestimated the runoff for most of the drainage areas located in higher latitudes. A linear river routing model was applied for the global runoff products from the LSMs and analyzed at 250 gauging stations. The correlations between observed and simulated monthly runoff were improved for most of the LSMs by introducing the routing. River runoff information was found to be effective for the validation of water cycles on the continental scale.A database for the GSWP products was developed with graphical user interface, and opened for the public accesses through the Internet. These global datasets consisting water and energy balances drew magnificient attention from public and the number of the access to the dedicated web page is increasing since its opening. Currently the access to the database is more than 5,OOO request per month.