Abstract: The Range of Variability Approach is used to quantitatively estimate the temporal and spatial variation of the hydrologic regime in the middlesection of the Hanjiang River after the impoundment of the Danjiangkou Reservoir. The results show the highest Indicators of Hydrology Alteration (IHA) in different stations and IHA groups, as well as the corresponding ecological impacts. It is demonstrated that the degree of discharge alteration in the lower reaches of Hanjiang River is rather moderate (range from 47% to 63%)， the degree of water surface elevation alteration is rather high， XiangYang and HuangZhuang have highest alteration of water surface elevation (proportion is 53% and 75%). More specifically， the water surface elevation decreased significantly at all stations (decreased 1～2 m). The frequency and duration of high/low flow pulses in Huangjiagang station of decreased (IHA is -0.49/-0.62 and -0.87/-0.74). The monthly mean and extreme values of discharge and water surface elevation at Huangzhuang and Xiangyang stations decreased, the frequency of discharge reversal magnitude increased (IHA is 1.82 in high RVA range). The occurrence of those Indicators that captured the effects of IHA on the four major Chinese carps was less frequent during the postdam construction period compared to that before the impoundment. The discharge and water surface elevation of the lower reaches decreased during the dry season, thus increasing the possibility of water bloom occurrence.
Key words：Danjiangkou reservoir impoundment; range of variability approach; indicators of hydrology alteration; temporal and spatial variation; ecological impacts