Multi-scale Analysis Of Diurnal Variation Of Urban Thermal Environment

With the progress of urbanization in China,the functional structure within the built-up areas of cities is becoming more and more complex.Local heat island effect appears within the city.The local heat island phenomenon poses a great threat to the quality of life of urban residents and the health of the habitat.Therefore fine assessment of heat and cold sources in local areas within cities is a key factor to improve urban living environment conditions.The current research on urban thermal environment and urban heat island is mainly focused on the dynamic monitoring of large-scale regional scale with long time series changes.The diurnal variation of urban local thermal environment in short time series is less studied.In this paper,three urban areas in the center of Guangzhou City are selected as examples,and high spatial and temporal resolution LST data are obtained through a multi-source LST fusion correction model to explore the community-scale LCZ classification method.The diurnal variation and spatial distribution characteristics of LST at three scales of community unit,land use function and building function are also analyzed to assess the diurnal variation characteristics of urban local thermal environment in short time series cycles.The main findings of this study are as follows:(1)The improved LST multi-source data fusion model can better obtain high spatial and temporal resolution LST data.And it reflects the spatio-temporal distribution characteristics of LST in the short time series cycle.Regarding the diurnal variation of LST,the maximum LST within the built-up area of the city appears at around 12:00 noon,while the minimum temperature appears at around 7:00 am in the early morning hours.Meanwhile,for the temperature difference between the maximum and minimum LST values in the study area at the same time,the temperature difference at night(around 20°C)is significantly smaller than that at daytime(around 25°C).In terms of spatial distribution heterogeneity,the high temperature areas within the city were mainly distributed in the central part of Haizhu District and the eastern part of Tianhe District.And the regions with lower temperatures are mainly distributed in the northeast and southeast of the study area where the permeable surface is relatively high.The global spatial autocorrelation shows that the significant P-values of the LST spatial distribution are all less than 0.001,with a level significant statistical difference.Local autocorrelation analysis reveals significant differences in the aggregation patterns at night and during the day.The nocturnal high aggregation area is mainly distributed in the western part of the study area,while the daytime increases a part of the area in the eastern part of the study area.It proves that daytime solar radiation and human activities change the spatial distribution characteristics of inner-city LST.(2)The community-scale local climate zoning method and criteria based on GIS database can accurately classify community categories in a scientific and reasonable manner.The study area has the most LCZc types of compact mid-rise(41.51%),compact high-rise(22.50%)and dense mid-rise.They are mainly distributed in Yuexiu District,west-central Haizhu District and southern Tianhe District.The sparse low-rise and greenfield types have a larger footprint,although the number of communities is smaller,and are mainly distributed in the northeast and southeast.In the diurnal variation of LST under LCZc classification,the impervious surface ratio has the largest image on LST,followed by community building density and finally community building height.In the effect of community building density on the diurnal variation of LST,the dense type is greater than the compact type than the sparse type.In the effect of community building height on the diurnal variation of LST,low-rise is greater than mid-rise than high-rise.(3)In terms of land use functional attributes.At night,the LST of various types of functional sites differed less,and the LST of areas with a higher percentage of permeable surfaces,such as green areas and non-construction sites,was higher.During the daytime,industrial land and logistics and storage land have the highest LST(32℃).The LST is lower(27℃)in areas with a higher percentage of permeable surfaces,such as green areas and non-construction sites.The spatial distribution of LST of different land uses types,on the other hand,shows the characteristics of high west and low east.In terms of building functions.The building types with the lowest nighttime and daytime temperatures are ROW and WS mixedfunction buildings,respectively.the highest LST building types are CWS and OW,respectively.The building type with the highest diurnal temperature variation is OW.the building type with the lowest temperature variation is WS.For the single category of building use function,the industrial building has the largest diurnal temperature variation of 12.30°C.In addition,the surface temperature of the soccer field in the study area was higher than the average temperature of the study area during the whole day and night time.