Comparative analysis of historical human and biogeomorphic interactions in large river-floodplain systems under different climate contexts

Abstract

Worldwide, trajectories of deterioration of large rivers’ natural structure and functioning have been described and related to anthropogenic pressures acting at different spatio-temporal scales. However, the variety of methodologies, time-scale resolutions and the lack of standard indicators frequently hinder the comparison of outcomes among rivers in different geographic and climatic regions. Covering between 204 and 36 years, this study applied the same multi-temporal analysis of riverine trajectories (i.e., anthropization, changeless, progression, and regression) in five large river segments within temperate (Rhine River, France and Germany), Mediterranean (Ebro and Tagus Rivers, Spain), and semi-arid climates (Aras and the Zayandeh-rud Rivers, Iran). This transferable GIS-based method includes the assessment of historical balances within natural dynamics (Natural Trajectory Index, NTI), the degree of anthropization (Anthropization Ratio, AR), and the degree of stability (Stability Ratio, SR) in the studied river-floodplain systems.Results show similarities among the European case studies (i.e., Rhine, Ebro and Tagus rivers) in response to hydromorphological impacts, with percentage increases in human-induced changes (i.e., anthropization), and habitat development (i.e., progression). Apart from the Zayandeh-rud River, that presents a marked tendency toward progression, processes of habitat rejuvenation (i.e., regression) have almost disappeared in all case studies, and riverine forms remain unchanged. The differences found between the European and the Asian case studies are considered related to the aims and methods of engineering choices for historical river management, with a long history of river reprofiling and impounding in European rivers, while Iranian regulation is relatively recent, and involves extensive inter-basin water transfers.