Using existing measurements of streamflow data, we present a new data set of fiver discharges to the ocean, for use in validating climate models. This data set includes annual mean discharges for 981 rivers, representing approximately 824,500 m3/s of global river discharge. This is about 65% of contemporary estimates of continental precipitation minus continental evaporation (P-E). Using our new data set, we present a self-consistent water budget over continents. We find that rivers with annual mean discharges between about 250 m3/s and about 20,000 m3/s closely follow a power law size distribution. We estimate the total flow from rivers smaller than 250 m3/s by assuming they obey the same power law size distribution. Under this assumption, the estimated total flow from these rivers is about 33% of P-E. Including an existing estimate of soil moisture entering the ocean underground, our estimated total flow into the ocean is within about 2% of contemporary estimates of continental P-E. Our data set is available in digital format. flux of fresh water into the oceans affects the ocean thermohaline circulation. Land-surface hydrology partially controls the rates of growth and decomposition of most vegetation species, and hence affects the global carbon cycle. Despite its importance, large-scale hydrology is typically treated with less sophistication than other aspects of global climate models. One reason for this is that validation of largescale land-surface hydrologic calculations is difficult. Most of the physical processes being modeled (evapotranspiration, soil moisture content, surface runoff, etc.) are extremely heterogeneous, and hence are difficult to measure on the large scale; thus, it is difficult to determine if model calculations agree with the observed hydrologic properties.The hydrologic cycle in climate models can be validated in part by using observed river discharge data. Computed continental river discharge can be compared to measurements of river discharge at gauge stations near significant river outlets. If the simulated flows agree closely with the observed river discharges, then confidence in the simulated hydrologic system is increased.
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