Long-term spatiotemporal variation and multiscale drivers of extreme tropical cyclones in the South China Sea

Abstract Based on tropical cyclone (TC) observation data over the South China Sea (SCS) from 1949 to 2023, this study analyzes the long-term changes in TC frequency, intensity, and duration. Using the generalized extreme value, we further identify and quantify the spatiotemporal characteristics of three categories of extreme TCs (ETCs) defined by maximum wind speed ( V max ), duration (Duration), and accumulated cyclone energy (ACE). The multiscale drivers behind these changes are also investigated. The results reveal an approximately 25% decrease in total TC frequency over the SCS in the past 75 years, with the most notable reduction occurring in locally formed TCs. Concurrently, the average Duration of TCs has increased by about 25%, while no significant trend is observed in mean intensity. ETCs exhibit metric-dependent changes: location parameters for V max - and ACE-based ETCs have declined significantly, whereas those for Duration-based ETCs have increased. Non-local ETCs contribute more substantially to the decreasing intensity trend, while local ETCs show prolonged residence within the basin. Spatially, the track density of both TCs and ETCs remains concentrated in the northern SCS, but has increased significantly for most TCs/ETCs in the Beibu Gulf Economic Zone of Guangxi Province and along the southwestern coast of Guangdong Province in China, as well as to the west of the Philippines, indicating a shift in regional exposure risk. Further analyses indicate that the El Niño–Southern Oscillation regulates ETC activity on interannual timescales, while the Pacific decadal oscillation and Atlantic multidecadal oscillation modulate ETC variability on decadal scales and likely contributed to the reversal in the trend of the V max -ETC location parameter around 2000. Moreover, V max -ETCs and ACE-ETCs are generally suppressed by vertical wind shear over both the SCS and the western North Pacific main development region, whereas the prolonged Duration-ETCs appear to depend on enhanced low-level vorticity, mid-level humidity, sustained upward motion, and higher convective instability within the SCS. This study highlights the multi-metric and multiscale characteristics of ETC activity in the SCS, providing important scientific value for regional disaster prevention and climate risk assessment.