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The coastal region of Bangladesh is repeatedly battered by major cyclones from the Bay of Bengal (BOB) almost every year. The majority of the destruction caused by cyclones in Bangladesh is due to storm surges that can completely inundate offshore islands and vast coastal areas, particularly the exterior coast, which is the first tier of the coastal belt. Therefore, a thorough investigation of cyclonic activity is crucial for effective disaster preparedness and mitigation strategies. This study addresses the urgent need for a comprehensive understanding of this phenomenon. It investigates 147 years (1877-2024) of landfalling tropical cyclones, also including the monsoon depressions, across the 12 exposed coastal districts of Bangladesh to develop a detailed and accurate dataset. The study also aims to determine the maximum possible surge levels for different return periods based on historical cyclonic activity. Analysis of past patterns reveals the likelihood of cyclone occurrence in 12 coastal districts, with Chattogram and Cox’s Bazar exhibiting the highest occurrence probability. The western and central coastal districts, including Shatkhira, Khulna, Noakhali, Patuakhali, and Pirojpur, experience a notably higher frequency of Tropical Cyclones and Monsoon Depressions during the monsoon period.
For the computation of maximum surge level, Bangladesh Delta Model (BDM), which is developed in the Delft3D numerical model platform, was simulated for the past 51 cyclones in a coupled surge-wave environment. Among all simulated scenarios, Feni district emerged as the most susceptible to extreme tidal surges, with a simulated maximum surge level of 6.98 meters. Frequency analysis further highlights the differential risks across districts. Feni district exhibits the highest 100-year surge level, reaching 5.93 meters. For Chattogram and Cox’s Bazar, there's a 1% chance of surge levels reaching 4.58 and 3.94 meters, respectively. In contrast, Bagerhat district has the lowest 50- and 100-year return period surge levels, at 2.04 and 2.21 meters, respectively.
For a holistic understanding of the collective impact, a tropical cyclone and monsoon depression hazard assessment was undertaken for the 12 coastal districts. The assessment indicated that Chattogram exhibited the highest and Lakshmipur was found to be the lowest on the tropical cyclone and monsoon depression hazard assessment among the 12 exposed coastal districts. A comprehensive understanding of historical landfall patterns can inform both short-term and long-term development strategies. Analyzing spatial and temporal variations in coastal surge behavior can help identify vulnerable areas and optimize mitigation efforts. Additionally, assessing maximum surge levels for different return periods can guide the design of resilient coastal infrastructure and polder systems. By gaining insights into the extent of the problem, relevant authorities can implement effective measures to reduce cyclone-related damage in Bangladesh. |
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