Monday, 10 February 2003
New Estimates of Continental Discharge and Oceanic Freshwater Transport
New estimates of freshwater discharge from continents were derived using stream-flow records from the world's largest 921 rivers, supplemented with estimates of discharge from unmonitored areas based on the ratios of runoff and drainage area between the unmonitored and monitored regions. The farthest downstream river-flow data were extrapolated to the river mouth using river transport model simulations forced by a runoff field. This new continental discharge estimate was then applied to estimate the meridional transport of freshwater within the oceans. The relatively new estimates of net water fluxes (P-E) over ocean surfaces derived from atmospheric moisture budget analyses based on the NCEP/NCAR and ECMWF reanalyses were used in the calculation of oceanic freshwater transport. Our results, which are improved in many aspects compared with previous estimates, show that global continental discharge is about 37288 km3 yr-1 (1.2 Sv, 1 Sv=1´106 m3 s-1) or about 35% of terrestrial precipitation. Compared with earlier indirect estimates of oceanic freshwater transport, our new estimates derived using the 921-river based discharge and the ECMWF reanalysis based P-E show improved agreement with available direct estimates for the Atlantic, Pacific, and Indian Ocean basins. The new estimates also show increased southward transports in the Atlantic Ocean and increased northward transports in the South Pacific Ocean.