Climate change effect on hydrological processes over the Yangtze River basin

Abstract

In order to investigate how the hydrological processes in the Yangtze River basin will be affected by climate change in the future, the regional climate model (RegCM3) nested in one-way mode within a NASA/NCAR finite volume element AGCM (FvGCM) is used in this study to generate IPCC SRES A2 emission scenario. Two sets of multi-decadal simulations at 20-km grid spacing for present day (1961–1990) and future climate (2071–2100, A2 scenario) are conducted. The results of the control experiment from 1961 to 1990 indicate that both the simulated annual averaged temperature and precipitation in the Yangtze River basin have distinct topographic characters and agree with the observations since the detailed topography of Yangtze River basin is incorporated into the high resolution of RegCM3. The simulated temperature of the Yangtze River basin is quite consistent with the observed one. It can reproduce more detailed structures of surface temperature distribution in annual, winter and summer average, which decreases from southeast to northwest and the cold bias is less of 1–2 °C. The simulated annual precipitation is less than the observation, while the result is better in summer than in winter although it may overestimate rainfall induced by topographic forcing at the Tibetan Plateau margin. Then the RegCM3 and a large-scale routing model (LRM) are linked to project the future climate change effects on hydrological processes over the Yangtze River basin. The results show that on average the evapotranspiration augments with a significant increase in temperature and a decrease in precipitation, while the spatial distribution is greatly inhomogeneous over the whole basin. The streamflow will also decrease especially in flood season from May to September which may aggravate the crisis of water resources shortage over the basin in flood season. The temperature increase will also lead to the augmentation in snow melt runoff, which may arise more often and earlier than spring runoff, and finally will provoke more changes in the seasonal rainfall-runoff processes and the allocation of the intra-annual water resources. The flood disaster should decrease in the main stream of the Yangtze River which may increase in the Hanjiang River basin.