Impact of land surface feedbacks on landfalling tropical cyclones

The Bay of Bengal experiences numerous cyclones during the pre-monsoon and post-monsoon seasons. The heavy rain associated with these cyclones causes devastating damage to life and property during landfall. The modern numerical weather prediction models and high temporal satellite observation data have significantly increased the accuracy of cyclone prediction in recent years. However, accurately predicting the intensity of rainfall and its dissipation after landfall is still a challenge. Previous studies have indicated that land-based evapotranspiration play an important role in determining the intensity and decay of cyclones post landfall (Evans et al., 2011; Tuleya, 1994). In this study, we quantify the contribution of land-based evapotranspiration to the rainfall associated with cyclones and the impact of land conditions on the speed and track of cyclones originating in the Bay of Bengal. In order to achieve this, we have adopted two techniques: a) using a tagged WRF model and b) a sensitivity study using different land conditions. The tagged WRF model will tag the evapotranspiration originating on land and track it throughout the atmosphere till it precipitates or moves out of the domain, whereas, the sensitivity study consist of simulations with dry and wet land conditions. This study simulates six cyclones originating in the Bay of Bengal and landfalling in India in the last decade. The cyclones selected are from pre and post-monsoon season and of various intensities. For analysis, the precipitation only within 500 km from the cyclone center are considered. The results show that the rainfall originating from land-based evapotranspiration is more significant as the cyclone approaches land than when it originates in the middle of the ocean. Therefore, the land-based evapotranspiration plays a crucial role in the end phase of the cyclone (from just before landfall till its decay). For the post-monsoon cyclones, the rainfall from land-based evapotranspiration is as high as 20% to 30% after landfall, whereas for pre-monsoon cyclones, the land contribution is around 10% to 15%.