Geo-ecological impact assessment of severe cyclonic storm Amphan on Sundarban mangrove forest using geospatial technology

Abstract

We report the damage caused by Amphan, a category five tropical cyclonic storm, to the ecology and shoreline of the Sundarban mangrove ecosystem, located in India and Bangladesh. In this study, net shoreline movement (NSM) combined with vegetation indices, such as normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI), were used to analyze land use and land cover changes and the position of the shoreline in pre- and post-cyclone periods. The results show that the cyclone wreaked havoc in the Sundarban mangrove ecosystem, causing dangerous impacts on vegetation and severe erosion along the shoreline. The impact on the Sundarban mangrove forest, shown by NDVI and EVI values, indicates that the mangrove vegetation suffered degradation and fragmentation. Dense and moderately dense mangrove tree cover area shrank from 77% to 34%, less dense and sparse cover increased from 20% to 63%. More than 68% of shoreline transects registered signs of erosion, with mean shoreline change and erosion rate measurements of −31 m and −48 m, respectively. As a result, agricultural lands and aquaculture ponds suffered inundation, leading to crop damage. A single cyclone episode can damage mangrove cover by knocking down tall trees, killing more salt-sensitive mangrove species such as Sundari, and leads to increased man-animal encounter. We argue that post-cyclone biodiversity loss and ecosystem services loss should be analyzed in tandem and synchrony with human and livestock casualty and economic damage assessment.