Study On The Diurnal And Intraseasonal Variations Of The Summer Surface Thermal Environment In The Yangze River Delta And Their Influences On The Diurnal Temperature Range

Knowledge of the surface thermal environment and daily temperature range(DTR)is of great scientific significance and practical application value for understanding the attribution,impact and response of regional and urban climate change in the Yangtze River Delta(YRD).We selected three provinces and one city in the Yangtze River Delta and divided them into three sub regions:the northern YRD(NYRD),the southern YRD(SYRD)and the metropolitan YRD(MYRD)that located in middle YRD.Based on the multi-source satellite datasets from 2013 to2017,using GIS technology and machine learning model,we systematically studied the spatial-temporal distribution characteristics of the surface thermal environment in the YRD in summer and its relationship with the daily temperature range.The main conclusions are as follows:(1)The obvious intraseasonal variation of DTR is in the NYRD,where the monthly averaged DTR in June is 8.6?,while its lower averages of 7.4? and 7.6? are in July and August,respectively,which is largely attributable to minimum surface air temperature(SATmin),due to nighttime land surface temperature(LST_N)responses to the underlying surface cover changes associated with crop rotation.(2)The summer DTR in the MYRD exhibits marginal intraseasonal variations,and the monthly averaged DTR in June is 7.0?,while its higher averages of 7.8? and 7.6? are in July and August,respectively.The reason is that the weather stations there are surrounded by a higher surface thermal environment and anthropogenic heat flux(AHF),the MYRD has stably higher land surface temperature(LST)and SATmin in the whole summer season.(3)In the SYRD,there is also a distinct DTR characteristic,and the monthly averaged DTR in June is 7.4?,while its higher averages of 9.4? and 9.0? are in July and August,respectively.Its DTR variation is mainly forced by sunshine duration(SSD),which directly affects maximum of surface air temperature(SATmax).In conclusion,although the temperature change is mainly affected by the solar radiation change,the regulating effect of human activities such as urbanization and agricultural production on the daily temperature range in the YRD in summer cannot be ignored.