Escalating typhoon risks in Shanghai amid shifting tracks driven by urbanization and sea surface temperature warming

Abstract. Tropical cyclones (TC) in the western North Pacific, known as typhoons, cause significant socioeconomic damage in East and Southeast Asian countries. The city of Shanghai in China is highly vulnerable to TC damages. For example, Typhoons Bebinca and Pulasan recently (September 2024) struck the city, resulting in widespread flooding, power outages, and the evacuation of more than half a million residents, while also breaking local rainfall records. Despite these threats, there is limited knowledge about the variability and mechanism of TC activities in this region under climate change and urbanization. Here, we use the Weather Research and Forecasting (WRF) convection-permitting model to simulate five TC events that made landfall along the southeastern coast of China and severely impacted Shanghai between 2018 and 2022. Different scenarios are conducted, including considering a future expansion of Shanghai's urban area and increases in sea surface temperature (SST) by 1, 2, and 3 °C. The results indicate that while SST warming significantly shifts TC tracks away from the city, the local risk continues to increase due to substantial enhancement of rainfall intensity and wind velocity. Warmer SST increases air temperature and decreases sea level pressure, thereby facilitating the formation and development of TC sizes and their dynamic systems. Furthermore, we find a consistent southward shift of the TC tracks that can be linked to the Fujiwhara effect, a phenomenon that occurs when two typhoons interact, causing a mutual counterclockwise rotation. Compared to SST changes, urbanization has limited influence on TC tracks and structures. The increase in surface roughness due to urban expansion reduces wind velocity but enhances the rainfall intensity within Shanghai, further exacerbating local risk. These findings could improve our understanding of typhoon variability under the combined effects of urbanization and climate change, as well as the risks they pose to Shanghai and other megacities in TC-prone regions.