Study on Ecological Water Requirement Estimation Methods in the Middle and Upper Reaches of the Yalong River Basin (Invited)

To determine suitable methods for estimating ecological water requirements in the middle and upper reaches of the Yalong River Basin, four representative hydrological stations—Ganzi, Zhuba, Daofu, and Yajiang—were selected. Ecological water requirements were calculated using the Q90 method, flow duration curve method, and the modified Tennant method. The applicability of each approach was comparatively evaluated. The results indicate that the Q90 method is computationally simple but fails to reflect the natural hydrological variability. The flow duration curve method (P = 95%) effectively captures seasonal variations in ecological water demand. However, its capacity to satisfy ecological requirements during fish spawning periods is relatively limited. By constrast, the modified Tennant method performs well in terms of ecological suitability during fish spawning periods, while its ecological environment evaluation is comparatively inadequate during regular water-use periods. Based on a comprehensive comparison of the advantages and limitations of the three methods, a time-segmented combined approach is proposed: the flow duration curve method is recommended for regular water-use periods, while the modified Tennant method is more appropriate for fish spawning periods and flood season. These findings provide technical support and a scientific reference for water resources protection and ecological regulation in the middle and upper reaches of the Yalong River Basin.