Ensemble projection of the sea level rise impact on storm surge and inundation at the coast of Bangladesh

The hydrodynamic model Delft3D is used to study the impact of sea level rise (SLR) on storm surge and inundation in the coastal region of Bangladesh. To study the present-day inundation scenario, the tracks of two known tropical cyclones (TC) were used: Aila (Category 1; 2009) and Sidr (Category 5; 2007). Model results were validated with the available observations. Future inundation scenarios were generated by using the strength of TC Sidr, TC Aila and an ensemble of historical TC tracks but incorporating the effect of SLR. Since future change in storm surge inundation under SLR impact is a probabilistic incident, a probable range of future change in the inundated area was calculated by taking into consideration the uncertainties associated with TC tracks, intensities and landfall timing. The model outputs showed that the inundated area for TC Sidr, which was calculated as 1860 km(2), would become 31% larger than the present-day scenario if a SLR of 0.26m occurred during the mid-21st-century climate scenario. Similarly to that, an increasing trend was found for the end-21st-century climate scenario. It was found that with a SLR of 0.54 m, the inundated area would become 53% larger than the present-day case. Along with the inundation area, the impact of SLR was examined for changes in future storm surge level. A significant increase of 14% was found in storm surge level for the case of TC Sidr at Barisal station if a SLR of 0.26m occurred in the mid-21st century. Similarly to that, an increase of 29% was found at storm surge level with a SLR of 0.54m in this location for the end-21st-century climate scenario. Ensemble projections based on uncertainties of future TC events also showed that, for a change of 0.54m in SLR, the inundated area would range between 3500 and 3750 km(2), whereas for present-day SLR simulations it was found within the range of 1000-1250 km(2) These results revealed that even if the future TCs remain at the same strength as at present, the projected changes in SLR will generate more severe threats in terms of surge height and the extent of the inundated area.