Climate Change Impacts on Runoff in the Upper Yangtze River Basin

This study examined the climate change and its impacts on water availability, runoff seasonality, extreme monthly runoff, and runoff spatial pattern in the upper Yangtze River basin using Soil and Water Assessment Tool (SWAT) model, based on a subset of five global circulation models under three Representative Concentration Pathways (RCP2.6, RCP4.5, RCP8.5). The projected average annual temperature presents a significant increasing trend, with an increase of 1.5~5.5°C by the end of the 21^st century relative to the reference period 1986-2005, and the overall precipitation is projected to increase since 2030s, with an increase of 5~15% by the end of the 21^st century. There is considerable spatial variation in the projected changes in annual temperature and precipitation across the upper Yangtze River basin, with the upper sub-basins (Jinsha River and Mintuo River) have a generally warmer and wetter conditions comparing with the whole study area. Changes of climate will result in an increase in the simulated mean annual runoff in the upper Yangtze River basin since 2030s, with an increase of 4~8% in middle of 21^st century, and 10~15% increase by the end of the 21^st century. There is no shift in season runoff pattern. Furthermore, the intra-annual distribution of monthly runoff is simulated generally more uniform. However, the inter-annual variation of runoff is simulated increase, which indicates more frequent and severe extreme flood and drought events. Climate change led to spatial differences in simulated runoff, the sub-basins of Jinsha River and Mintuo River show a relative small change in the annual water availability as well as the inter-annual and intra-annual variability, whereas the sub-basins of Jialing, Wu, and mainstream of the upper Yangtze River simulated a larger increase in water availability and hydrological extremes. All these changes in hydrological response reflect the local heterogeneous in sensitivity to global climate change, which is useful for local climate change adaptation and basin management.