Using cruise observations before and after the typhoon Chebi in August 2013 and those without the typhoon in July 2012, this study investigates variations in current structure, nutrient distribution, and transports disturbed by a typhoon in a typical coastal upwelling zone east of Hainan Island in the northwestern South China Sea. The results show that along-shore northeastward flow dominates the coastal ocean with a volume transport of 0.64 × 10⁶ m³/s in the case without the typhoon. The flow reversed southwestward, with its volume transport halved before the typhoon passage. After the typhoon passage, the flow returned back northeastward except the upper layer in waters deeper than 50 m and the total volume transport decreased to 0.10 × 10⁶ m³/s. For the cross-shelf component, the flow kept shoreward, while transports crossing the 50 m isobath decreased from 0.25, 0.12 to 0.06 × 10⁶ m³/s in the case without the typhoon as well as before and after typhoon passage, respectively. For the along-shore/cross-shelf nutrient transports, SiO₃²⁻ has the largest value of 866.13/632.74 μmol/s per unit area, NO₃⁻ half of that, and PO₄³⁻ and NO₂⁻ one order smaller in the offshore water without the typhoon. The values dramatically decreased to about one-third for SiO₃²⁻, NO₃⁻, and PO₄³⁻ after the typhoon, but changed little for NO₂⁻. The disturbed wind field and associated Ekman flow and upwelling process may explain the variations in the current and nutrient transports after the typhoon.

Tropical cyclones (TCs) pose a significant threat in terms of wind-induced damage and storm risk to the Guangdong–Hong Kong–Macao Greater Bay Area (GBA) of China. In this research, annual power dissipation index (PDI) and storm surge and wave destructive potential (SDP) index from June to November were used to estimate the damage caused by the TC events in the buffer zone of the GBA. The regime shifts in 1993 and 2013 were identified through the Bayesian changepoint detection in six TC datasets. The TC-induced damage during 1994–2012 (the low-damage period) was weaker than that in 1977–1993 and 2013–2020 (the high-damage periods). The intensity and size of stronger TCs are the dominant factors responsible for the interdecadal changes in the TC damage. This may be explained by the influences of sea surface temperature (SST), surface latent heat flux and mid-level relative humidity. During high-damage periods, TCs can extract more energy from the ocean, leading to increased TC intensity and larger size. Conversely, during low-damage periods, TCs undergo a decrease in energy intake, resulting in reduced TC power and smaller size. The variations in the SST are relative to the Luzon Strait transport. In addition, the reduction in TC translation speed is unfavorable for the development of TCs in low-damage periods. Further research suggested that mid-level steering flow affects the TC movement velocity. The results offer valuable insights into the variations in the TC-induced damage in the GBA.

This study develops a systematic framework for assessing the temporal dynamics of tropical cyclone (TC) risk in the Guangdong–Hong Kong–Macao Greater Bay Area (GBA) from 2013 to 2023. A unified composite index was constructed by integrating hazard, vulnerability, and mitigation capacity, allowing for the quantification of the interannual evolution of TC risk. The analysis showed that maximum storm surge and extreme precipitation drove hazard variability, with distinct peaks during the super typhoons of 2017 and 2018. In the vulnerability dimension, GDP and population density together accounted for over 50% of the total weight, and the vulnerability index shows an upward trend, though its growth slowed in 2020. Mitigation capacity improved steadily, accelerating after 2020 and partly offsetting the risk pressure from growing vulnerability. The risk index broadly mirrored the hazard index, peaking in 2018. Notably, in the two TC-free years (2014 and 2019), the risk index was higher in 2019 than in 2014, reflecting an increased vulnerability-to-mitigation ratio over the intervening period. A coherence check against three disaster loss indicators (2018–2023) yielded a correlation of r = 0.8, indicating broad consistency in the interannual patterns of the risk index and observed losses. This study provides a temporally explicit baseline for understanding recent TC risk dynamics and offers methodological support for resilience planning in coastal megaregions facing climate-related hazards.