Although changes in the annual number of global TCs are controversial 11 , 13 , 14 , an increasing trend in the number of global intense TCs has been noted 12 , 14 , and significant efforts have been devoted to reducing uncertainties in data quality issues 15 , 16 .
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In both the NH and the SH, the occurrence time of intense TCs shows a significant trend towards earlier onset at the 95% confidence level based on a non-parametric statistical test (‘Statistical significance’), with rate of 3.7 and 3.2 days per decade, respectively (Table 1 ).