The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

The southeastern coastal region of China is recognized as one of the high-frequency areas for warm-sector heavy rainfall in presummer rainy season. These heavy rainfall events are characterized by abrupt onset, high intensity, and limited predictability, posing great threats to society and economy. Within weakly forced synoptic environment, the unique complex terrain over southeastern coast in China become crucial for the evolution of warm-sector heavy rainfall and associated convective systems. 

This work aims to investigate the impact of multiscale topography during an unprecedented heavy rainfall event in May 2018, when over 270mm of rain was observed in three hours in Xiamen, reaching a centennial precipitation level in the southeastern coastal area. Using the Barnes filter to separate different scales (large, meso- and small scale) of terrain over southeastern coastal region, convection-permitting WRF simulations and terrain sensitivity experiments are performed to investigate how multiscale topography modulates the features of the extreme heavy rainfall and mechanisms of associated convective systems.

Preliminary results reveal that convection was triggered early in the morning around the Lianhua Mountain in eastern Guangdong associated with mesoscale terrain feature. This convection gradually organized into a quasi-linear system aligned parallel to the coastline and continued to move northwestward. Notably, this organizational pattern is closely related to the Boping Ridge and Daiyun Mountain in Fujian. Additionally, at the small-scale terrain near Zhangzhou, multicells continuously merged, enhancing the intensity and contributing to the persistent heavy rainfall in this event.

In future, we will further explore the influences of the multiscale terrain on the essential convective environments for this extreme heavy rainfall event by comparing the terrain sensitivity experiments in detail, aiming to elucidate their synergistic contributions to the extreme rainfall.

extreme heavy rainfall, southeastern coast, multiscale terrain, convective systems