Understanding Controls on Historical River Discharge in the World’s Largest Drainage Basins

Long-term (20 yr) river discharge records from 30 of the world’s largest river basins have been used to characterize surface hydrologic flows in relation to net precipitation inputs, ocean climate teleconnections, and human land/water use patterns. This groundwork study is presented as a precedent to distributed simulation modeling of surface hydrologic flows in large river basins. Correlation analysis is used as a screening method to classify * Corresponding author address: Dr. Christopher Potter, NASA Ames Research Center, Moffett Field, CA 94035. E-mail address: [email protected] Earth Interactions Volume 8 (2004) Paper No. 2 Page 1 eint-07-07-08 Wednesday, 28 January 2004 1:45 pm Allen Press, Inc. Page 1 river basins into categories based on major controls on discharge, for example, climate, land use, and dams. Comparisons of paired station records at upstream and downstream discharge locations within each major river basin suggest that the discharge signals represented in upstream discharge records are sustained in the downstream station records for nearly two-thirds of the drainage basins selected. River basins that showed the strongest localized climate control over historical discharge records, in terms of correlations with net basinwide precipitation rates, are located mainly in the seasonally warm temperate and tropical latitude zones, as opposed to river basins located mainly in the higher latitude zones (above 458N). Ocean climate indices such as the Niño1þ2 and Niño3þ4 correlate highly with historical interannual patterns in monthly river discharge for only four of the selected discharge station records, namely, on the Amazon, Congo (Zaire), Columbia, and Colorado (Arizona) Rivers. Historical patterns of cropland development and irrigated areas may explain the weak climate correlations with interannual patterns in monthly river discharge rates for at least one-third of the major river drainages selected from the historical discharge dataset. This paper is part of a special theme issue on land use and ecosystems.