The Interannual Variation And Influencing Factors Of Summer Accumulated Temperature In My Country Under Different Thresholds

Under the background of global warming,the impact of summer high temperature events is increasing,and the heterogeneity of the occurring regions is obvious.In the study,the summer accumulated temperature is used to reflect the intensity of summer high temperature.The relative effects on the accumulated temperature for internal statistical characteristics,that is,the frequency and intensity,are quantified.The relative effects with different thresholds and the trends of the effects with the change of the thresholds are analyzed.For regions with similar characteristics of variation in relative impact,the thresholds for their respective regional accumulated temperature are given.By comparing with other commonly used high temperature indices,the significance of regional accumulated temperature in real-life applications is discussed.The interannual variation of accumulated temperature and regional distinguish of external influencing factors were also analyzed.The conclusions are as follows:(1)When a relative lower threshold is used to define "high temperature" days,the main influencing factor of the summer accumulated temperature at the station is the intensity.The relative effect of intensity on accumulated temperature gradually decreases from south to north in the eastern region,with the opposite trend in the western region.In the east-west direction,the relative effect of intensity effects tends to decrease from east to west in the middle and low latitudes,and the opposite in the high latitudes.When a relative higher threshold is used,the main influencing factor is the frequency.(2)The results of the dominant analysis of summer accumulated temperature are sensitive to changes in thresholds,and the results change when different temperatures are used as thresholds.For a station,with the increase of threshold,the effect of intensity on accumulated temperature gradually decreases,while the effect of frequency increases.For the national stations,in the process of increasing the threshold,the number of stations which dominated by intensity are decreases.(3)The results of the dominant analysis showed significant regional differences in sensitivity to threshold changes.According to the regional characteristics of variation rate,five regions were selected and their regional characteristics were analyzed.For each area,the "recommended" threshold is given,respectively: I is 28.5 ?;II is 30.8 ?;III is 32.3 ?;IV is 32.7 ?;V is 29.6 ?.The distribution is basically consistent with the national summer high temperature.In this paper,these temperatures are used as thresholds for regional accumulated temperature.Compared with the commonly used 35 ?,the regional threshold has its own practical significance: it is more flexible and applicable to areas with relatively low summer temperature,such as high latitude and high altitude;it reflects the variation characteristics of both frequency and intensity in a more balanced way;it reduces the errors caused by regional climate differences in the comparative analysis.(4)By comparing with other common high temperature indexes in Changchun station and Nanjing station,the reflection effect of regional accumulated temperature threshold on summer high temperature in practical application is analyzed.Taking the region I and region III,which located in the northeast region and the lower Yangtze River region as examples.The results of the reflection of the accumulated temperature under the regional threshold are compared with those of the commonly used high temperature index,so as to analyze the accuracy and the advantages of the regional accumulated temperature.The results show that,compared to 35 °C and 32 °C,the regional thresholds are more appropriate as thresholds for accumulated temperatures.The regional accumulated temperature has better reflection than HWDI and WSDI in the intra-seasonal scale,and better reflection than Tmax with higher temperature variability.The results of regional accumulated temperature are more comprehensive in terms of correlations,variation trends,abrupt years,and extreme years,and are more closely related to regional warming.The proposed and used of regional accumulated temperature perfects the summer high temperature index for high latitudes region.(5)In the analysis of the affecting factors,it is found that the regional accumulated temperature is negatively correlated with precipitation,precipitation days and total cloud cover,but positively correlated with solar radiation.However,the degree of influence of each factor on the accumulated temperature varied in different regions.Overall,the regional accumulated temperature correlated best with the solar radiation and worst with precipitation.