Changes in Continental Freshwater Discharge from 1948 to 2004

• Main Authors: Dai, Aiguo, Qian, Taotao, Trenberth, Kevin E., Millliman, John D.
• Format: Text
• Language: unknown
• Published: W&M ScholarWorks 2009
• Subjects: Freshwater; Streamflow; Precipitation; Rivers; Runoff; Physical Sciences Peer-Reviewed Articles; Fresh Water Studies; Arctic; Pacific; Indian; Uruguay; Yenisey
• Online Access: https://scholarworks.wm.edu/vimsarticles/1968; https://doi.org/10.1175/2008JCLI2592.1; https://scholarworks.wm.edu/context/vimsarticles/article/2966/viewcontent/2008jcli2592_1.pdf

A new dataset of historical monthly streamflow at the farthest downstream stations for the world’s 925 largest ocean-reaching rivers has been created for community use. Available new gauge records are added to a network of gauges that covers ∼80 × 106 km2 or ∼80% of global ocean-draining land areas and accounts for about 73% of global total runoff. For most of the large rivers, the record for 1948–2004 is fairly complete. Data gaps in the records are filled through linear regression using streamflow simulated by a land surface model [Community Land Model, version 3 (CLM3)] forced with observed precipitation and other atmospheric forcings that are significantly (and often strongly) correlated with the observed streamflow for most rivers. Compared with previous studies, the new dataset has improved homogeneity and enables more reliable assessments of decadal and long-term changes in continental freshwater discharge into the oceans. The model-simulated runoff ratio over drainage areas with and without gauge records is used to estimate the contribution from the areas not monitored by the gauges in deriving the total discharge into the global oceans. Results reveal large variations in yearly streamflow for most of the world’s large rivers and for continental discharge, but only about one-third of the top 200 rivers (including the Congo, Mississippi, Yenisey, Paraná, Ganges, Columbia, Uruguay, and Niger) show statistically significant trends during 1948–2004, with the rivers having downward trends (45) outnumbering those with upward trends (19). The interannual variations are correlated with the El Niño–Southern Oscillation (ENSO) events for discharge into the Atlantic, Pacific, Indian, and global ocean as a whole. For ocean basins other than the Arctic, and for the global ocean as a whole, the discharge data show small or downward trends, which are statistically significant for the Pacific (−9.4 km3 yr−1). Precipitation is a major driver for the discharge trends and large interannual-to-decadal variations. ...