Attribution Of Extreme High Temperature Events In China In 2018 Based On The Circulation Similarity Method

High temperature and heatwave(HT and HW)directly impact human health and crop growth.The identification and attribution of the high temperature and heatwave event will help to understand the relative contribution of natural climate change and human climate change,so we can provide important scientific information for people's production and life and the formulation of adaptation and mitigation measures.In this paper,the flow analogue method is used to analyze the attribution of the extreme high temperature event in summer 2018 in typical area of China.First of all,this paper analyzes the long-term trend background of the occurrence rate of high temperature heat wave event in China from 1960 to 2018,and expounds the importance of using appropriate trend analysis method.By showing a case of the annual count of HT days with extremely excessive occurrences in 2018 at a station in northeastern China,we illustrate that the least square method(OLS)is sensitive to outliers and can give spurious trend.Then through normality testing and autocorrelation calculation,we find at least 91.14% of stations and 90.06% of grid boxes for the annual count of HT days and 92.18% of stations and 87.74% of grid boxes for the annual count of HW in China are non-Gaussian,and the majority of them have serial correlation.There,applying a nonparametric method that is insensitive to outliers and takes into account serial correlation,this paper gives a more accurate estimation of the linear trends in the annual count of HT days and HW for every station and grid box,four typical regions average,and China area-average for the period 1960?2018.The results show that stations with statistically significant increasing trend in HT days occur mainly in South China and northwestern China,and those in HW occur nearly only in South China and several stations in Xinjiang Autonomous Region.In terms of area average of the trend in annual count of HT days and HW,only South China region and northwestern China region show statistically significant increasing trend,whereas North China and northeastern China not significant;those of China average are both significant.Then,based on the flow analogue method,the two extreme high temperature event indicators(daily minimum temperature and regional high temperature days)in North and Northeast China in summer of 2018 are analyzed.It is found that the event cannot be explained solely from the perspective of atmospheric circulation.Finally,the sensitivity tests of the three parameters(similar sampling interval,similar measurement and circulation variable)of the flow analogue method are carried out.It is found that the changes of the first two will not significantly change the results of the flow analogue,but which circulation variable is selected will have a certain impact on the results.However,under the three tests,the extreme high temperature event in North and Northeast China cannot interpreted solely from the perspective of atmospheric circulation,this main conclusion remain unchanged.