QUANTIFYING ANTHROPOGENIC AND CLIMATE CHANGE IMPACTS ON HYDROLOGIC REGIME ALTERATIONS

Abstract

Anthropogenic interventions and climate change have altered the natural flow regime of river systems around the world. A comprehensive understanding of specific contributions and influences made by each of these factors in the hydrologic alteration is vital for sustainable water resources development and management. The present study analyses the flow regime changes in few significant river basins due to human-induced activities (e.g., dam construction, landuse change, etc.) and climate change. The study focuses on analysing the flow regime alterations through various scenarios defined according to the pre- and post-impact datasets using Indicators of Hydrologic Alteration (IHA) quantified through the traditional and improved Range of Variability Approach (RVA), Histogram Matching Approach (HMA), and Histogram Comparison Approach (HCA). The study also investigated the potential of the sample entropy method as an information measure to evaluate the alterations in the river system in addition to the ecologically relevant IHAs. The present study was carried in the Roanoke River Basin located in the United States and the Godavari and Krishna River Basin in India. In the first part, the degree of hydrologic alteration of the Roanoke River was quantified under three different scenarios using the traditional and improved RVA which incorporates indices of periodicity (IP), trend (IT), and symmetry (IS) of the IHA parameters. For this purpose, different scenarios were defined as scenario-I (containing pre-impact series from 1913-1949 and post-impact series from 1956-1991) as used by Richter et al. (1996), scenario-II (having pre-impact series from 1913-1949 and post-impact series from 1991-2016) representing the extended post-impact period, and scenario-III (having pre-impact series from 1913-1949 and post-impact series from 1956-2016) indicating the whole length of data available for the analysis. The alterations results obtained with the traditional and improved RVA approach were compared with the HMA method for a comprehensive analysis. The principal component analysis (PCA) was used to identify the most ecologically relevant hydrologic indicators (ERHIs). The improved RVA analysis reveals that many IHA parameters exhibited a higher degree of periodicity (IP), trend (IT), and symmetry (IS) in comparison to the alteration values obtained by using the traditional RVA, underscoring the inadequacy of the traditional RVA approach to estimate the hydrologic alterations correctly. The comparative analysis of RVA and HMA also indicates that the adoption of the combined approach provides a more comprehensive assessment of the flow regime alteration.