The Sundarbans and the Coastal Flooding in Bangladesh

Bangladesh is considered to be one of the most vulnerable countries to floods and tropical cyclones. Cyclone SIDR (2007) caused $1.7 billion in damages and almost 10,000 deaths. However, the presence of coastal mangrove forests greatly mitigated the cyclone’s lethal impacts. The largest mangrove forest in the world, the Sundarbans, is located in Bangladesh. Despite being the world’s largest mangrove ecosystem with an area of 7900 square miles, the Sunderbans mangrove is currently in decline. Agriculture, fishing, farming and settlement all have an impact on the Sunderbans mangrove ecosystem, which is rapidly being destroyed. The destruction of the Sunderbans mangroves and the resulting storm surge flooding are the focus of this study. In this section, we consider two unlikely but plausible outcomes: Consideration of two scenarios: (1) converting the entire mangrove cover to an estuarine wooded wetland, and (2) turning it into grassland entirely. We used a framework that incorporated a geographical assessment of mangroves vegetation with numerical simulations to estimate the benefits of the mangrove forests in this location to reduce storm surge. A high-performance computing environment and a hydrodynamic model (ADCIRC) with a wave model (SWAN) were used to estimate the storm surge. With the help of Cyclone SIDR (2007) meteorological inputs, an unstructured numerical mesh with 200,000 nodes was built and validated at six Bangladesh coast locations. The impacts of mangrove degradation on flood inundation and storm surge magnitude were studied in 27 model simulations including nine cyclones of different classifications. For category 3 storms, simulations showed that the loss of mangroves to grassland could boost the surge elevation by as much as 57% and increase the flood wave velocity by as much as 2730%. For low intensity cyclones, the inundation inland penetration and total inundated area would increase by almost 10 km and 18%, respectively. The existing Sunderbans mangroves play a critical role in reducing surge height, velocity, inundation penetration, and flooded areas, as these hypothetical situations show. The continued degradation of this crucial ecosystem has the potential to negatively affect future cyclone-induced dangers in this area, which is also shown in this study.