Multi-dimensional parametric coastal flood risk assessment at a regional scale using GIS

Coastal floods are the most prominent natural disaster causing severe damages to the local communities regarding food security, economy and shelter. Risks can be defined by physiographical sensitivity and vulnerability associated with socio-economic, demographic and infrastructure aspects of the region. Population with poor socio-economic status and high dependence on natural resources for livelihood in coastal dwellings of rural India are extremely vulnerable to flood hazards. Policy formulation to reduce coastal flood risks necessitates quantifying hazard vulnerability at an administrative scale. In this context, we propose a method for evaluating the coastal flood risk of an island located in the habited part of Sundarbans, West Bengal. Extending up to 282 sq. km, Sagar Island has been a keystone in harbouring and supporting both local and migrant population since the 1880s. Land-use classification of the island indicates an increase of 1.7% to 3.6% in the built-up class, almost double in the past eight years (2012–2020). A considerable rise in area under the water bodies is also seen from 6.6 to 8.6%, signifying fair evidence of a coastal breach. Flood risk assessment of Sagar Island was carried out using high spatial resolution data from Indian remote sensing satellites and census data. This assessment was performed by modifying the established MCDA technique considering the data limitations and accounting accessibility to infrastructure as a novel variable to a multi-dimensional framework. The framework maps spatial vulnerability of the region using sub-factors such as socio-demographic, economic, infrastructure and accessibility. The exposure profile of the area is drawn with the help of topographic factors and classified land-use results. Literature evidence was used to develop classification rules for data standardization from very high to very low based on their flood sensitivity. Further, the factors and sub-factors were ranked using AHP by a panel of experts belonging to diverse fields such as disaster management, regional planning, environment, hydrology and social science. The weighted sum technique was used to quantify total vulnerability and exposure parameters, respectively. The total risk map generated is the product of the hazard and vulnerability map of the region. The findings reveal the dominance of economic and accessibility parameters in defining the vulnerability of the regional population towards coastal flood risks. Proximity to coastline and tidal creeks enhances disaster sensitivity due to frequent inundation, erosion, saltwater intrusion and complete submergence of land area. Water bodies engulfing the coastline emerge as a serious threat to sustenance given the present rate of submergence of about 6 m/year. The research highlights the pressing need for grassroots development through social and economic upliftment. It also advocates the undeniable need for proactive adaptation such as flood resilient housing and coastline protection by stabilizing sandbars and planting/nurturing/maintaining native species (mangroves).