A Histogram Comparison Approach for Assessing Hydrologic Regime Alteration

Abstract

The histogram comparison approach (HCA) is proposed to assess the alteration of hydrologic regimes, which are characterized by the hydrologic metrics, for example, the indicators of hydrologic alteration. The HCA method considers alterations within the whole range of the hydrologic regime and estimates the alteration degree by comparing the pre‐impact and post‐impact histograms. A key parameter of the HCA method is the similarity degree, which considers both the class‐by‐class and cross‐class information of histograms and reflects how many features of the pre‐impact histogram remain in the post‐impact histogram. The alteration degree is defined as the mathematical maximum similarity degree, that is, 100%, subtracted by the actual similarity degree in the HCA method. Comparing the HCA method to the existing range of variability approach and histogram matching approach through theoretical analysis and case studies, the HCA method can eliminate some limitations of the range of variability approach and histogram matching approach methods and can more accurately and effectively assess the hydrologic regime alteration. The Ob and Yangtze Rivers, which are located in different climatic zones, are used as case studies. Hydrologic regime alterations impacted by reservoirs with different regulation abilities (daily, seasonally and yearly) were assessed using the HCA method, the results of which verified its rationality and practicability. More sites with a wider range of flow variations will be examined in the future to assess the applicability of the HCA method. Copyright © 2017 John Wiley & Sons, Ltd.

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

“…Suen et al (2010) analyzed the relationship between climate change and hydrological regime alteration in Taiwan. Hydrologic parameters Group 1: Magnitude of monthly water conditions However, RVA does not fully assess the hydrological alteration because only the occurrence changes in the middle range are considered to represent the hydrological regimes [Huang et al, 2017]. Here we verify this argument by a set of real discharge data (Figure 1).…”

Estimation of Hydrologic Alteration in Kaligandaki River Using Representative Hydrologic Indices

“…The HCA method is based on class by class correspondence and cross-class correspondence of the information in data [23]. Histograms for 32 IHA indices are constructed and their frequency vectors are compared using two similarity metrics.…”

“…Those two similarity metrics are combined to form a single similarity metric, which is used to calculate the dissimilarity and in turn the alteration. Alteration by the HCA method is discussed in detail by Huang et al (2017) [23]. The overall degree of alteration is calculated using a group average technique as given by Xue et al (2017) [43] and the final value is represented by "A".…”

“…The RVA method, however, does not consider the variation of parameters falling within the target range and those outside the range, sometimes seriously underestimating the degree of alteration [22]. Using IHA indices, the Histogram Matching Approach (HMA) and its subsequent extension Histogram Comparison Approach (HCA), we considered the alteration on whole flow regime, unlike the RVA approach which only considered alteration within a predefined target range [22,23]. Furthermore, HCA performed better than HMA in providing judgment on alteration because it considered cross-class correspondence in addition to class-by-class correspondence [23].…”

“…Using IHA indices, the Histogram Matching Approach (HMA) and its subsequent extension Histogram Comparison Approach (HCA), we considered the alteration on whole flow regime, unlike the RVA approach which only considered alteration within a predefined target range [22,23]. Furthermore, HCA performed better than HMA in providing judgment on alteration because it considered cross-class correspondence in addition to class-by-class correspondence [23]. HCA also considered the alteration related to the hydrologic year types (HYT) i.e., wet, average and dry years, however, it failed to consider the alteration of their order.…”