Research Paper Migrating rivers, consequent paleochannels: The unlikely partners and hotspots of flooding K.S. Sajinkumar a,b, ⁎, A. Arya a,c , A. Rajaneesh a , T. Oommen b , Ali P. Yunus d , V.R. Rani e , Ram Avatar f , K.P. Thrivikramji g a Department of Geology, University of Kerala, Thiruvananthapuram 695 581, Kerala, India b Department of Geological & Mining Engineering & Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA c Pondicherry University, Port Blair, Andaman and Nicobar Islands 744103, India d Center for Climate Change Adaptation, National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506, Japan e Central Ground Water Board, Thiruvananthapuram 695 004, Kerala, India f Graduate School of Environmental Science, Faculty of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan g Centre for Environment and Development, Thiruvananthapuram 695013, Kerala, India HIGHLIGHTS • Role of paleochannels in floods was deciphered through this study. • Paleochannels were identified through a multitude of methods. • The flood water was extracted through multiple radar datasets. • Paleochannels in midlands have a fast discharge when compared to lowlands. • Paleochannels can be considered as paths for flood discharge during unprec- edented rain. GRAPHICAL ABSTRACT abstract article info Article history: Received 11 August 2021 Received in revised form 3 October 2021 Accepted 3 October 2021 Available online 8 October 2021 Editor: Fernando A.L. Pacheco Furious floods have become an omnipresent reality with the dawn of climate change and its transition to adult- hood. Since climate change has now become an accepted reality, analysing the factors that favour or disfavour floods are an urgent requirement. Here we showcase the role of paleochannels, a product of migrating rivers, in a catastrophic flood in the south-western part of the Indian Peninsula. This study exposes whether these geo- morphic features facilitate or impede floods. For the purpose of extracting paleochannels and floodwater map- ping, we utilized multiple satellite datasets and took advantage of diversified feature selection algorithms. Paleochannels were demarcated viz., initial identification of a few paleochannels from literature and confirma- tion through high-resolution Google Earth (GE) images, followed by Principal Component Analysis (PCA) of Sentinel-2 images using Google Earth Engine (GEE), and a supervised classification of the principal bands 1, 2, and 3. False-positives were eliminated using Object-Oriented Analysis (OOA), which reduced the 964,254 poly- gons to 23,254. These polygons were visually affirmed using GE images that resulted in 115 paleochannels as the final collection. A few locations were verified through Vertical Electrical Sounding (VES) using the Schlumberger method. The features were analysed with the floodwaters of the 2018 catastrophic flood, extracted from Syn- thetic Aperture Radar (SAR) data, which was delineated for different temporal limits including the day of peak flood of August 17, 2018. During the peak flood, the inundation of the study area extended to 534.86 km2 with all the paleochannels getting immersed in floodwater. After 44 days of peak flood, the post-flood analysis Keywords: 2018 Kerala flood Paleochannel River migration Object Oriented Analysis Principal Component Analysis Science of the Total Environment 807 (2022) 150842 ⁎ Corresponding author at: Department of Geology, University of Kerala, Thiruvananthapuram 695 581, Kerala, India. E-mail address: sajinks@keralauniversity.ac.in (K.S. Sajinkumar). https://doi.org/10.1016/j.scitotenv.2021.150842 0048-9697/© 2021 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv