Forecasting and Evaluation of Impacts and Risk Due to Tidal Anomalies on a Coastal Island

Assessment and forecasting of exposures, vulnerability and risks due to natural forces are important for the survival and adaptation of local communities. This research intends to understand the risk and impact associated with sea level rise and tidal amplitude on a coastal island located in the cyclogenesis area of the Bay of Bengal. Three scenarios were developed based on tidal amplitudes of 2 m, 4 m and 6 m, respectively, relative to the observed tide heights during extreme events. Land use analysis indicated a severe loss of natural vegetation in the last century, i.e. from 103 to 9 km 2 with an increase in cultivated spaces by 69 km 2 , and in the last 8 years, post-cyclone Aila built-up spaces have increased by 4.7 km 2 (2012–2020). Local topography derived from stereo satellite data and the N8 connectivity bathtub model was used to determine flood inundations for various surge amplitudes. Analysis indicates the rising sea levels would inundate additional 275 ha of coastal lands, and built-up spaces would increase by 17.8 km 2 by 2050. Exposure assessment illustrates that during severe cyclonic events and super cyclonic events, tides engulf 27–187.7 km 2 landmass in the current era (2020), while by 2050, the cumulative effect of the surge and sea level rise would lead to exposure of 35.7–203.8 km 2 of the landscape. Risk assessment shows that during a less intense severe cyclonic event, 19.5 ha (2020) and 36.8 ha (2050) of built-up areas towards the east coast would be under high risk, whereas in extremely severe events, the built-up spaces under high risk would increase to 127 ha (2020) and 166 ha (2050) across the island. The analysis shows the importance of forecasting exposures and risks due to the variations in climate and landscapes. The frequency and intensity of low pressures cyclones in the cyclogenesis area are increasing with time.