A revised range of variability approach considering the morphological alteration of hydrological indicators

Abstract

A reasonable assessment of the hydrological regime alteration is a prerequisite for river utilization, restoration, and protection. The hydrological alteration is quantified as changes in different indicators (IHAs) identified by Range of Variability Approach (RVA). However, RVA is unable to reveal the morphological characteristic which demonstrates the overall hydrological regime. This will lead to an incomplete assessment of the hydrological alteration. To supplement the current assessment, this work proposed a revised RVA method in three main steps: (1) to identify the morphological characteristics of each IHA; (2) to quantify the morphological alteration by comparing the Hasse matrices of different time series; (3) to combine the frequency alteration and morphological alteration of IHAs for reflecting overall hydrological alteration. A case study of the upper Yellow River shows that the revised RVA method outperforms RVA in the assessment of the hydrological regime not only because revised RVA captures the hydrological changes of certain IHAs that are not reflected by conventional RVA, but also the alteration identified by revised RVA shows more apparent differences at two stations upstream and downstream the dam than conventional RVA can provide. The revised RVA is more applicable to identify the hydrological alteration due to dam construction which could have negative impacts on river ecosystem since the morphological alteration of time series is considered. As a whole, the new method offers a better understanding of the alteration in hydrological regime, which gives beneficial guidance to river management.