Effect of roughness length using LULC on the wind intensity of tropical cyclones and its associated inundation

     India is frequently affected by coastal flooding due to storm surges that significantly effects human lives, coastal infrastructure, and marine ecosystem. Tropical cyclones (TCs) are the most severe storms especially over the Bay of Bengal (BoB) and the Arabian Sea (AS). The vulnerability from the TCs occurs in many ways, which include coastal inundation by extreme water levels, damage of coastal properties caused by strong cyclonic winds, additional flooding caused by cyclone-induced heavy precipitation. The destruction along the coast due to inundation enhances if the cyclone makes landfall near the estuaries, river deltas, or any adjoining rivers in the coastal area. Simulation of inland flooding requires accurate representation of topography and surface roughness over the flood plain. Incorporating Land Use/ Land Cover (LULC) data in numerical simulations help in introducing roughness which alter the cyclonic wind speed over land. This also enhances model capabilities to represent accurate wind during the cyclone period. In the present study, experiments are carried out to simulate extreme water elevations and associated coastal inundation for the recent TC, Yaas (2021) that occurred over the BoB using stand-alone ADCIRC (Advanced circulation) model coupled ADCIRC and SWAN (Simulating Wave Nearshore) model. High-resolution mesh is used to incorporate major river systems and water bodies. Various datasets like Airborne DEM, CARTOSAT-DEM, SRTM-DEM, MIKE-CMAP, and ETOPO-2 are used to prepare the model mesh. The results show that total inundation calculated by the coupled model is higher since the SWAN model gives an extra momentum flux to the ADCIRC model in the form of radiation stress gradient. This results generation of maximum water elevations in the coupled model. As the TC approaches over the land, wind intensity gets reduced due to the presence of different land covers, which have specific roughness lengths. The more the roughness length, higher will be the reduction in the wind speed. To observe modifications in the wind speed over the land and ocean, ERA-5 reanalysis data is used for the 1999 Orissa super cyclone, Hudhud (2014), Amphan (2020), and Nivaar (2020). The results show a reduction of 38.2%, 35.62%, 16.35%, and 29.58% in wind speed at the time of landfall over the land compared to that of over the ocean for the above cyclones respectively. Using standalone ADCIRC and coupled ADCIRC+SWAN model, the simulations are made for TC Vardah (2016) to study the impact of roughness length over the wind intensity based on LULC. The results suggest that there is a significant decrease in the wind intensity over land after modifying the roughness length.