基于生态径流指标的水文情势变化评估新方法

基于流量历时曲线计算生态径流指标的方法存在诸多不足，也未形成相应的河流水文情势变化评估方法。采用流量过程线重新定义了月、季和年三种时间尺度的生态径流，构建了包含12个月生态盈余和12个月生态赤字的生态径流指标体系，提出了衡量这些指标在建库前后变化度的计算公式，基于月生态赤字发展了月生态风险评估方法，形成了一种河流生态水文情势变化评估方法。将其用于长江宜昌站，评估三峡工程在建库前后的生态水文情势变化。结果表明：重新定义的月、季、年生态径流之间消除了不一致性，香农多样性指数与年生态赤字的年际变化具有更高的相似度，变化度计算公式完全适用于衡量建库前后的变化程度，生态风险图使生态径流指标的实用性大为增强。

New method for evaluating changes in hydrologic regimes based on eco-flows metrics

The method for calculating eco-flows metrics based on flow duration curves has some limitations, and no evaluation system is yet available for the alterations of hydrologic regimes based on eco-flows metrics. This paper first constructs an index system including twelve month eco-surpluses and twelve month eco-deficits, through refining monthly, seasonal and annual eco-flows metrics based on discharge hydrographs. A formula measuring the degrees of change in these indexes is derived, and an ecological risk assessment method based on monthly eco-deficit is worked out. Then, we develop a new method for assessing the alterations of hydrologic regimes, apply it to the Yichang hydrologic station of the Yangtze River as a case study, and evaluate the changes in its hydrologic regimes caused by the Three Gorges project. Results show that the redefinition of the monthly, seasonal and annual eco-flows metrics eliminates the inconsistencies, significantly improving the similarity of the diversity index of Shannon to its annual eco-deficit based on discharge hydrographs. The formula is effective in evaluating the degree of regime changes, and the ecological risk graph helps greatly in enhancing the applicability of eco-flows metrics.