Spatiotemporal Features And Causes Of The Summer Extreme Heat Stress In China During 1961-2016

Under the background of global warming,extreme events occur frequently.Heat waves are common extreme weather events in China in summer,which directly endangered human health and affected the normal operation of production and life.Based on the heat stress index,the daily mean temperature and relative humidity data of 1,814 weather stations over China from 1961 to 2016 and the NCEP / NCAR reanalysis data were used to analyze the interannual variability of heat stress and possible influencing factors in China.The main results are as follow:The heat stress index combines the characteristics of two meteorological elements in monthly variability,interannual variability,and spatial distribution.In terms of seasonal variations,the heat stress index grew in June,reached its highest point at the end of July,and then declined in mid-August.In terms of interannual variations,the heat stress index showed a downward trend before the mid-1970 s,rose slowly after the mid-1970 s,and began to increase in the 1990 s.In terms of spatial distribution,the Qinghai-Tibet plateau is the low value region of heat stress index,and the value in other regions decreases from southeast to northwest.The probability distributions of heat stress days(HSD)?heat strss frequency(HSF)and heat stress last time(HSL)are positive skewness.The main modes of the empirical orthogonal function decomposition of the three indexes were all of the region-consistent type,and the corresponding time coefficients were changed from negative to positive in the mid-1990 s,indicating that HSD?HSL and HSF increased relatively after the mid-1990 s.In terms of interannual variability,all three indexes have increased significantly since 1990.In terms of spatial distribution,the low value areas of the three indexes are located over the western Sichuan,however,the high value areas of HSL are located over the western Qinghai,Gansu and Inner Mongolia.The interannual variation of extreme heat stress events in the northern China experienced an interdecadal transition around 1990.Before 1990,the interannual variability of the frequency of extreme heat stress events was relatively small,and its interannual variation was mainly affected by the Eurasian teleconnection pattern,Antarctic Oscillation,and East Asia-Pacific teleconnection pattern.After 1990,the interannual variability of extreme heat stress frequency significantly increased and it was mainly affected by East Asia-Pacific teleconnection pattern.An anomalous quasi-barotropic anticyclonic circulation is controlled over the Huaihuai Region and the South China,respectively,when the HSF are higher than normal over the above regions.Correspondingly,marked positive SSTAs and an El Nino-like SSTAs dominate over the East China Sea and tropical Indian and Pacific Oceans,respectively.