Spatiotemporal variations of inter- and intra-annual extreme streamflow in the Yangtze River Basin

Climate change has led to anomalous fluctuations in extreme streamflow from global river systems, and the superposition of human activities such as damming has compounded the changes in extreme streamflow, affecting floods and river ecosystems. However, muti-temporal scale variations of extreme streamflow and the dominant driving factors were limitedly understood. In this study, we examined the changing patterns of inter- and intra-annual extreme (maximum 1-day, consecutive 3-days and 7-days) streamflow (including magnitude and timing) in the Yangtze River Basin (YRB) from the 1940 s to 2020. Furthermore, the roles of ENSO events and dams on temporal anomalies of extreme streamflow at inter- and intra-annual scales were identified in the whole basin. We found that the annual streamflow extremes increased in the source YRB and the middle and lower YRB but decreased in the upper YRB. The extreme streamflow during spring and autumn was characterized by increasing trends in the source and decreasing trends in other reaches. The occurrence timing of winter extreme streamflow in the upper and middle YRB was significantly delayed. The inter-annual extreme streamflow in the source and upper YRB had a negative relationship with ENSO, while the positive relationship held in the middle and lower YRB. The major anomalies (>50 %) of annual extreme streamflow generally occurred in ENSO (1+2) yrs, while precipitation contributes to the seasonal distribution of extreme streamflow. There was a good correlation between precipitation and both annual and summer extreme streamflow in the lower YRB, but the relationship completely shifted in the upper YRB after 2003. Further, the construction of dams has severely affected extreme streamflow, leading to a stepwise drop in annual and summer/autumn flows and a sudden rise in spring/winter flows. This study facilitates the prediction of extreme streamflow and the development of sustainable basin management strategies.