Changes in Flood Regime of the Upper Yangtze River

Abstract

River flooding affects more people worldwide than other natural hazards. Thus, analysis of the changes in flood regime caused by global warming and increasing anthropogenic activities will help us make adaptive plans for future flood management. The nonstationary flood behavior in the upper Yangtze River was examined comprehensively in terms of trend, change point, and periodicity with co-usage of different methods. Results show that there are decreasing tendencies in the corresponding series of annual maximum flood peak flow and flood volume in four out of six control stations, except Pingshan and Wulong stations in the Jinsha River and the Wu River, respectively, and the flood peak occurrence time appears earlier mostly. The uniformity of flood process increases in four main tributaries, while it decreases in mainstream of the Yangtze River (Yichang and Pingshan stations). The rates of both rising limb and recession limb of all the typical flood process flowing through the six stations were analyzed. 77.8% of the rates of rising limb decrease, while 61.1% of the rates of recession limb increase, which is almost consistent with the variation reflected by the uniformity. The change points of most evaluation indicators happened in 1970s–1990s. The first main periodicity of evaluation indicators in Yichang is about 45 years, while that of other stations is about 20 years. Invalidity of stationarity in the flood series can be attributed to the intensified construction on major water conservancy projects, changes of underlying surface, and influences of climatic variables. The contributions of both climatic control and the Three Gorges Dam (TGD) to the variation of the annual flood peak in Yichang station were further quantitatively evaluated, which has verified that the construction of the TGD has played a positive role in peak-flood clipping.

Hydrological Extremes in the Upper Yangtze River Over the Past 700 yr Inferred From a Tree Ring δ18O Record

“…This trend is consistent with the decreasing trends in the annual maximum flood peak flow and flood volume over recent decades based on the hydrological stations in the UYR (Y. Zhang, Fang, et al, 2021). Our findings can be supported by ancient inscriptions evidence which show that severe hydrological droughts have occurred more frequently over recent decades in the UYR (Qin et al, 2020).…”

“…Peak streamflow in the UYR occurs during the summer season (Figure S1 in Supporting Information ). Previous study has shown that this region is dominantly influenced by ISM in boreal summer (Y. Zhang, Fang, et al., 2021; Y. Zhang, Li, et al., 2021). We also used the monthly gridded (2.5° × 2.5°) pressure, wind, and specific humidity (300500 hPa isobar data) data from the NCEP/NCAR reanalysis data set (Kalnay et al., 1996) to analyze the direction and distribution total water vapor flux over the study region and the surroundings.…”

“…Previous study has shown that this region is dominantly influenced by ISM in boreal summer (Y. Zhang, Fang, et al, 2021;Y. Zhang, Li, et al, 2021).…”

“…Zhang, Fang, et al, 2021). However, the short length of observation records makes it difficult to assess the temporal patterns of these hydrological extremes and identify the associated mechanisms involving natural variability and anthropogenic warming (Chen & Wu, 2014;Wei et al, 2013;Y. Zhang, Fang, et al, 2021), especially over decadal and centennial timescales (Fang et al, 2018;Gu et al, 2018;Wu et al, 2021).…”

“…Observations indicate that the annual streamflow and flood volume in the UYR is decreasing (Y. Zhang, Fang, et al, 2021). However, the short length of observation records makes it difficult to assess the temporal patterns of these hydrological extremes and identify the associated mechanisms involving natural variability and anthropogenic warming (Chen & Wu, 2014;Wei et al, 2013;Y.…”