Storm surge flooding in the ganges-brahmaputra-meghna delta: present and future scenarios

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M. M. Rahman, Anisul Haque, R.J. Nicholls, M.A. Jisan, I. Ahmed, F. Nihal, A.N. LÁzár

Tuesday 30 june 2015

11:15 - 11:30h at North America (level 0)

Themes: (T) Extreme events, natural variability and climate change, (ST) Hydrological extremes: floods and droughts

Parallel session: 5I. Extreme events - FloodDrought

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It is widely believed that the nature and frequency of the cyclonic/storm surge floods generated from tropical cyclones of the Bay of Bengal will be changed in future with climate change which will pose future challenges to the coordinated management and planning (both short term and long term) in the Ganges-Brahmaputra-Meghna (GBM) delta. In addition to sea level rise and changes in the upstream flows associated with climate change – subsidence and sedimentation/erosion will also affect the nature of future storm surge floods in the GBM delta. To study the present and the future storm surge flooding patterns in this region, the two components of the Delft 3D modeling suite (the morphology model and the storm surge model) is applied to study the flooding scenarios. The floodplain sedimentation/ erosion is superimposed on the land subsidence and it is found that the impact of land subsidence is largely compensated by the net land elevated due to floodplain sedimentation if the present day sediment concentration prevails until mid and end centuries. The horizontal and vertical inundation patterns of two recent storm surge floods due to cyclones Aila (landfall location outside the region) and Sidr (landfall location inside the region) are studied. Scenarios of future storm surge floods are generated for the two time horizons – mid-century and end-century by incorporating sea level rise, sedimentation/erosion, land subsidence and fluvial discharge considering climate changes. The wind and pressure fields, cyclone tracks, landfall locations and landfall timings for both the cyclones are used as input to generate the surge and the resulting inundation. Predicted results reveal the fact that even if the future cyclones remain with the same strengths, same landfall locations and timing as it is at present (say, Sidr-like and Aila-like cyclones), the change of hydrodynamic and morphodynamic drivers will generate a more severe storm surge inundation scenarios both in terms of surge height and extent of inundation area. The above findings are part of ESPA Deltas Consortium project (www.espadelta.net) and would be useful to the programs for delta level planning of the GBM Delta or in other delta having the similar socio-ecological-physical condition.