Discharge of major global rivers in the late 21st century climate projected with the high horizontal resolution MRI-AGCMs


Correspondence to: Tosiyuki Nakaegawa, Meteorological Research Institute, Tsukuba, Japan.

E-mail: tnakaega@mri-jma.go.jp


This study used an atmospheric general circulation model (AGCM) with a 20-km grid spacing and a global river routing model with 0.5° grid resolution to project climatological mean river discharges in the late 21st century under a changing climate. We also performed an ensemble simulation with the same AGCM except with a resolution of 60 km and forced with different lower boundary conditions to quantify the level of confidence in the projections. By the late 21st century, projected annual mean river discharges increased in the high latitudes and in India and the southeastern United States but decreased in broad regions of Europe, western Asia, the western United States, Central America, and the southern half of the Amazon River basin. Projected future changes in monthly river discharges include unique seasonal details not present in the annual discharge projections: in the Amazon River, for example, river discharges were projected to increase in the high-water season but decrease in the low-water season. These seasonal changes suggest that monthly river discharge projections should be useful for assessing the human impacts and risks in future planning of water resources and flood control. We devised a way to measure the consistency between the various projections made by our 60-km ensemble simulations and our standard 20-km high-resolution model. Wherever the projected changes were consistent, the future changes also tended to be statistically significant in our high-resolution model. These results encourage a future projection of discharge for a specific river basin in the world. Copyright © 2013 John Wiley & Sons, Ltd.