Inhomogeneous trends in the onset date of extreme hot days in China over the last five decades

基于1960-2018年均一化日最高气温(T_(max))资料,发现中国大部分区域高温初始发生日期(FirstEHD)呈提前趋势,但华北地区一些站点呈推迟趋势,这主要由上述区域T_(max)的长期变化趋势决定,但T_(max)变率的影响也不可忽视.FirstEHD的变化趋势在1990s出现年代际转折,其中新疆,华北和长江流域在1990s前后FirstEHD发生变化,华南地区则表现为1990s前后FirstEHD趋势幅度的不同,但符号保持不变;研究表明FirstEHD趋势的年代际转折转折与大气环流年代际趋势的变化紧密相关.

Using a homogenized daily maximum temperature(T_(max))dataset across China,this study characterized the spatiotemporal variation of the onset date of extreme hot days in a year(i.e.,FirstEHD)during 1960-2018.Inhomogeneous trends of FirstEHD over China during 1960-2018 can be found,with the advanced trend of FirstEHD over most parts in China,while a number of stations in North-Central China(NC)show the delayed trend of FirstEHD.Moreover,there exist interdecadal changes of FirstEHD trend,with a remarkable difference in the trend magnitude before and after the 1990s over South China(SC),and the sign of trend can even reverse from negative to positive after the 1990s in Xinjiang(XJ)and Yangtze River Basin(YR),and from positive to negative in NC.The overall trends of FirstEHD over NC,YR,and XJ during 1960-2018 are dominated by the trends before the 1990s,while they are dominated by the sharp advance after the 1990s over SC.It is further found that the trend of FirstEHD can generally be explained by the long-term trend in T_(max) over most parts of China,but the contribution from T_(max) variabilities is also non-negligible and can even account for more than 75% of the overall trend over NC.The possible factors responsible for the decadal changes in FirstEHD trends are also discussed.