Climate change trend and causes of tropical cyclones affecting the South China Sea during the past 50 years

Tropical cyclones (TCs) in the South China Sea (SCS) cause serious disasters and loss every year to the coastal and inland areas of southern China. The types of TCs are usually difficult to forecast, and studies on the understanding of the TCs affecting the SCS are lacking. In this study, the authors use the TC data during 1965-2017 from two best-track datasets to analyse the climatic characteristics in terms of the frequency, the track activity, and the influencing indexes of the TCs affecting the SCS and investigate the possible causes. The results show that, during 1965-2017, there were 535 TCs affecting the SCS, mainly occurring from June to November of each year, with the annual average frequency exhibiting a significant downward trend. Meanwhile, the frequency of the track activity in most areas of the SCS also demonstrate a remarkable decreasing trend but an increase in the Gulf of Tonkin and the Taiwan Strait. The large-scale environmental anomalous westerlies and the decrease of humidity in the mid- and low-level over the northern part of the SCS are likely the main causes for the decrease in frequency and the track activity. In addition, the analysis using the cyclone activity index shows that the influence of the before mentioned TCs in southern China gradually decreases, while the influence of TCs in the SCS show a decreasing trend during past decades.