Comprehensive evaluation of watershed ecohydrological risk and ecohydrological satisfaction characteristics from the perspective of hydrological variability

Abstract This study quantifies the degree of hydrological regime alteration in the middle and lower reaches of the Yangtze River (MLYR) by incorporating the indicators of hydrologic alteration (IHA) along with six additional indicators. The ecohydrological risks are analyzed using the eco-surplus and eco-deficit indicators. Furthermore, the ecohydrological satisfaction index (ESI) is proposed to characterize the degree to which hydrological conditions meet the eco-water demand of rivers. The results indicate that the concentration period is delayed, and the complexity of hydrological processes is increased in the MLYR. Regarding the variability of hydrological conditions, except for Datong station with a change degree below 0.5, the other stations have experienced high changes. At the annual scale, the eco-surplus and eco-deficit of the MLYR basin have changed with the alteration degree of 0.41 and 0.37, respectively, and the eco-deficit of the mainstream exceeds the eco-surplus, indicating high ecohydrological risks. The ESI at Yichang station has significantly decreased, with the most pronounced decrease occurring in February (−0.35). The ESI of tributaries in the MLYR remains stable, with periods when the ESI at Huangzhuang station exceeds 0.8 accounting for more than 80% of the period from 2004 to 2021.