Satellite-based assessment of the August 2018 flood in parts of Kerala, India

Abstract

From 1 June to 29 August 2018, Kerala, a state in southwestern India, recorded 36% excess rainfall than normal levels, leading to widespread floods and landslides events and resulting in 445 deaths. In this study, satellite-based data were used to map the flood inundation in the districts of Thrissur, Ernakulam, Alappuzha, Idukki and Kottayam. Specifically, flood delineation was enabled with Sentinel-1A radar data of 21 August 2018 and was compared with an average pre-flood, water-cover map based on Modified Normalized Difference Water Index (MNDWI) that was developed using a January and February 2018 Sentinel-2A dataset. A 90% increase in water cover was observed during the August 2018 flood event. Low lying areas in the coastal plains of Kuttanad and the Kole lands of Thrissur, had marked a rise of up to 5 and 10 m of water, respectively, during this deluge. These estimates are conservative as that the flood waters had started receding prior to the August 21 Sentinel-1A imagery.

Keywords:

• Kerala flood
• August 2018 flood
• Sentinel-1A
• Flood Inundation Mapping
• Modified Normalized Difference Water Index

Acknowledgements

Oommen and Coffman thankful to the National Science Foundation (NSF, USA) sponsored Geotechnical Extreme Events Reconnaissance (GEER) Association for underwriting the cost of travel to Kerala, India, to verify and document the flood footprint that is reported herein. Authors acknowledge the editor and the anonymous reviewer for constructive comments.

Disclosure statement

No potential conflict of interest was reported by the author(s).