Assessing Flood Inundation and its impacts Using Sentinel-1A SAR Data and the Sentinel Application Platform in the Indus River Basin

Abstract

Flood disasters have become increasingly frequent and severe in Pakistan over the past few decades. In this study, Sentinel‑1A Synthetic Aperture Radar (SAR) data were employed to map flood inundation and assess the damage caused by the 2022 flood in four severely affected districts of Upper Sindh, Pakistan. SAR, with its all-weather and day‑and‑night imaging capabilities, serves as a vital tool for timely and accurate flood damage assessment. Sentinel‑1A imagery from August 28, 2022, was processed using the Sentinel Application Platform (SNAP) to capture peak inundation. Flood mapping was performed using histogram thresholding on both VV and VH polarizations, with VH polarization proving more effective in distinguishing water from land surfaces. Results revealed inundation exceeding 6,210 km², impacting over 1,928 settlements, primarily villages and hamlets. Critical infrastructure suffered major disruption, including 113 km of railway lines, 3,171 km of roadways, and 13 healthcare facilities out of 343. Agricultural losses were substantial, with rice, sugarcane, and cotton crop fields reduced by up to 50% in some areas. These findings highlight the effectiveness of SAR‑based flood mapping in rapid disaster assessment, particularly in cloud‑covered or inaccessible regions, and provide disaster management authorities with a reliable tool to enhance emergency response and inform future flood risk mitigation strategies.