An Improved Methodology for Risk Assessment of Tropical Cyclones Under Changing Climate

Tropical cyclone-related natural hazards are well known for resulting in the largest contribution to insured losses each year. High winds in the tropical cyclone boundary layer cause widespread damage to life and property in coastal areas. This situation has become more challenging due to the changing climate and increasing coastal population density. The hurricane track modeling framework for risk assessment generally consists of five essential components to simulate the whole track of tropical cyclone from its genesis to dissipation, namely hurricane genesis model, tracking model, intensity model, decay model, and wind field model. This study proposed a methodology to assess the climate change impacts on the wind field of tropical cyclones by advancing the hurricane track modeling approach. Firstly, several plausible tracking models were proposed and compared to offer an enhanced simulation of the tropical cyclone translational velocity and heading angle. Then, a new intensity model was derived from a simplified dynamic system for tropical cyclone intensity prediction to more effectively integrate the sea surface temperature (SST) and hence the climate change scenarios into the hurricane intensity. Conventional consideration of the effects of climate change on the hurricane intensity is to use a statistical model that relates the non-dimensional relative intensity to SST, which is not supported by the historical data as the results from the HURDAT database actually suggest that the SST should not be included in this statistical model. Furthermore, a new empirical formula of the maximum potential intensity (MPI) was used in the proposed intensity model to impose a physical limit associated with the hurricane intensity. In addition to SST as the major driving element of the intensity change of hurricanes, the moisture content was also integrated into the consideration of climate change simulations through the lapse rate. The Intergovernmental Panel on Climate Change (IPCC) pointed out in its recent released report that the moisture content is expected to increase significantly with global warming, and will lead to a smaller lapse rate. The lapse rate is an important parameter in the meteorology science to consider the negative feedback from global warming and hence increased moisture. The historical tropical cyclone database HURDAT was used to calibrate the proposed statistical models, and then the Monte Carlo simulation was employed to simulate the spatial and temporal evolutions of the tropical cyclone from the initial point to the dissipation stage. Good agreement between the proposed model and the historical hurricanes data was observed. The future climate scenarios have been integrated into the model to assess the effect of global warming on hurricane wind field through the SST and the change of moisture content through the lapse rate. The hurricane simulation results suggest that while the hurricane frequency will not significantly change, the intensity will increase following the projected climate change scenarios especially for the case of the Representative Concentration Pathway scenario 8.5 (RCP 8.5). The vertical profile of the wind speed in the boundary layer region was also investigated to highlight a considerable change in the vertical distribution of wind field due to the increase of moisture content.