Impact of Climate Change on River Discharge Projected by Multimodel Ensemble

TLDR

Changes in upstream runoff influence downstream river discharge, mirroring spatial patterns of precipitation and runoff shifts. The study projects 21st‑century river discharge for 24 major rivers using 19 coupled GCMs under the A1B scenario. A weighted ensemble mean of the 19 GCMs is employed to reduce bias and uncertainty in the projections. The weighted ensemble accurately reproduces current discharge and projects that by 2100 precipitation, evaporation, and runoff will rise in high‑latitude regions, southern/eastern Asia, and central Africa while falling in the Mediterranean, southern Africa, southern North America, and Central America, resulting in increased discharge and earlier peaks in high‑latitude rivers and reduced flow in Mediterranean and southern U.S.

Abstract

Abstract This study investigates the projections of river discharge for 24 major rivers in the world during the twenty-first century simulated by 19 coupled atmosphere–ocean general circulation models based on the Special Report on Emissions Scenarios A1B scenario. To reduce model bias and uncertainty, a weighted ensemble mean (WEM) is used for multimodel projections. Although it is difficult to reproduce the present river discharge in any single model, the WEM results produce more accurate reproduction for most rivers, except those affected by anthropogenic water usage. At the end of the twenty-first century, the annual mean precipitation, evaporation, and runoff increase in high latitudes of the Northern Hemisphere, southern to eastern Asia, and central Africa. In contrast, they decrease in the Mediterranean region, southern Africa, southern North America, and Central America. Although the geographical distribution of the changes in precipitation and runoff tends to coincide with that in the river discharge, it should be emphasized that the change in runoff at the upstream region affects the river flow in the downstream region. In high-latitude rivers (Amur, Lena, MacKenzie, Ob, Yenisei, and Yukon), the discharge increases, and the peak timing shifts earlier because of an earlier snowmelt caused by global warming. Discharge tends to decrease for the rivers in Europe to the Mediterranean region (Danube, Euphrates, and Rhine), and southern United Sates (Rio Grande).