Spatial And Temporal Characteristics And Influencing Factors Of Wet Bulb Temperature At The Block Scale In The Suburbs Of Nanjing

Global climate change and local urban heat island aggravate urban heat stress,but researches on urban neighborhood scale are still rare.Wet-bulb temperature can indicate the combined effect of temperature and humidity,and therefore can more accurately reflect human thermal comfort.By using mobile measurement method,temperature,relative humidity and geographic information were simultaneously collected under different seasonal and weather conditions in 2019 and 2020 for Jiangbei New Area of Nanjing and the spatio-temporal characteristics of wet-bulb temperature?T_win urban neighbourhood were investigated.In addition,the influence of sky condition,surface land cover and urban morphological index(Sky View Factor,SVF)on wet-bulb temperature were further analysed.The results showed that:(1)the diurnal and seasonal variation of?T_wshowed similar pattern:daytime?T_wwere higher than that of nighttime;the order of seasonal?T_wwere:summer>autumn>winter for2019 clear sky condition and 2020 all sky conditions(that of 2019 overcast sky condition were:autumn>winter).There was significant difference of?T_wbetween 2019 and 2020.(2)Daytime high?T_wvalues often appeared in area with sparse vegetation and open sky,while low values occurred in the area with contrary condiiton;in the nighttime,high?T_wvalues usually appeared in area with dense buildings and population,while low values can be found from area with dense vegetation,open sky and that near water bodies.In addition,for those with distinct seasonal landcover change the spatial variation of?T_wwould also change accordingly.The spatial variation range of daytime?T_wunder both clear and overcast sky condition followed the pattern as summer>autumn>winter,and there was no consistent pattern for nighttime.(3)On sunny days,both?T_wand difference of?T_wbetween daytime and nighttime were greater than that on overcast days;the spatial distribution of?T_wwas more uniform on overcast than on sunny days on the condition that landcover and morphological structure were the same.(4)There was significant positive correlation between SVF and daytime?T_w.The correlation and increasing rate of?T_was SVF went higher were much stronger under clear sky condition than that under overcast sky condition;the correlation between SVF and nighttime?T_wwere weak.(5)There were negative correlation between vegetation fration and?T_w,while impervious surface fraction were positively correlated with?T_w.These correlations were stronger and more statistically significant on overcast days.(6)The horizontal scale effect had distinct diurnal and seasonal differences:it was smaller in daytime than in nighttime and it grow bigger in cold season.These results can provide effective scientific support and theoretical basis for improving and optimizing thermal environment of urban neighborhoods as well as alleviating urban heat stress.