Hydrologic alteration and possible underlying causes in the Wuding River, China.

Understanding hydrological alteration of rivers and the potential driving factors are crucial for water resources management in the watershed. This study analyzed the daily runoff time series at six gauging stations during 1960-2016 in Wuding River basin, northwestern China. The Mann-Kendall test and Lee-Heghinian method were employed to detect the temporal trends and abrupt changes in annual streamflow. The flow duration curve (FDC) and the index of hydrologic alteration (IHA)/Range of Variability Approach (RVA) were applied to assess the daily streamflow and degree of hydrologic alteration (DHA). In addition, we analyzed the changes of index of hydrological connectivity (IC) and reservoirs/dams (RI) in 1990, 1995, 2000 and 2015 in the basin. The relationship between IC, RI and DHA were assessed to investigate the potential influences of land use changes and constructions of reservoirs/dams on hydrological alteration. The results indicated that annual streamflow at five stations showed significant downward trends (p < 0.01) from 1960 to 2016, and an abrupt changing point appeared in the beginning of 1970s in Wuding River basin. Exception is Qingyangcha station without significant changes, and Hanjiamao station with changing point in 1967. FDC analysis indicated that both high and low flow indices reduced greatly. The integral DHA were higher than 70% at all the stations in the Wuding River basin, suggesting great variation in the magnitude, duration, frequency, timing and rate of change of daily streamflow. Both IC value and RI had close relationship with DHA, implying that DHA was highly affected by land use changes and dams/reservoirs constructions, and was more sensitive to the land use change (p < 0.01). This study provides good insight to understand the effects of soil and water conservation measures on hydrological regime.