Impact of Meteorological Forcing on Storm Surge & Inundation in Coastal Bangladesh: A Comparison between Holland's Analytical Model and a Coupled Atmosphere-Ocean Model

The coastal region of Bangladesh experiences frequent flooding due to storm surge and inundation associated with the passages of Tropical Cyclones (TCs). To study the impact of storm surge and inundation in that region, Delft3D, a hydrodynamic model based on the shallow water equations, has been employed. Two major tropical cyclones, TC Sidr (2007, Category 5) and TC Aila (2009, Category 1), which made landfall in coastal Bangladesh, have been selected for this experiment.

While running the simulation, two different approaches have been used to generate the input meteorological forcing. In one experiment, input wind speed and sea surface pressure fields have been generated using Holland’s (Holland 1980) analytical wind and pressure equation. Best track data for both TCs are from the India Meteorological Department (IMD).

In the other experiment, the meteorological output from an interactively coupled atmosphere-ocean model has been used as input in the Delft3D model to generate the storm surge and inundation. In this case, the model-generated wind speed and pressure fields for both TCs have been validated against the observation before they were utilized in the hydrodynamic model.

Modeled water levels based on these two experiments are compared with the observations by the Bangladesh Inland Water Transport Authority. Storm surge generated using the wind and pressure field from the coupled atmosphere-ocean model showed better agreement with observations than the one generated using Holland’s equation. Also, the inundated area has been compared for both these cases and compared to each other.

Keywords: Storm Surge, Holland’s Model, Coupled Atmosphere-Ocean, Delft3D, Bangladesh, Coastal Flooding, Tropical Cyclones