Air Temperature Estimation Of Urban Street Valley In Qinhuai District Of Nanjing Based On The Cluster Thermal Time Constant Model

In recent years,China's economy has developed rapidly and the process of urbanization has been accelerating.The expansion of urban area has destroyed a large area of natural environment,changed the attributes of underlying surface,and has an important impact on urban microclimate,resulting in serious heat island effect and urban high temperature problems.Urban street canyon,as a basic component of the city,has an important impact on urban development and urban residents' life.Therefore,it is of great significance and scientific value to study the temporal and spatial distribution of air temperature in urban street canyon and the mechanism of microclimate influence,and to explore the influencing factors of urban thermal environment change.Based on the principle of urban surface energy balance,this paper uses cluster thermal time constant(CTTC)model to estimate street canyon temperature,combines ENVI-met microclimate model and reveals the spatial and temporal distribution and change mechanism of street canyon temperature at the block scale on the basis of air temperature estimation,which provides scientific basis for urban planning and thermal environment improvement in Nanjing.In the current study of urban thermal environment,the numerical simulation method is mostly used to simulate the instantaneous temperature dynamics of urban street canyons.However,the numerical simulation method needs more input parameters and strict boundary control conditions.The combination of reference meteorological observation data and numerical simulation method can reduce the input parameters and improve the accuracy of temperature estimation.Taking Qinhuai District of Nanjing as an experimental research area,this paper firstly uses CTTC model to obtain the quantitative influence of sensible heat flux and artificial heat radiation on the temperature change according to the principle of urban surface energy balance,designs temporal and spatial distribution parameters of artificial thermal radiation,then estimates the temperature of urban street canyon based on the observation data of reference stations,and analyses its quantitative influence on the accuracy of temperature simulation by changing the parameters that may affect the simulation results.Finally,the accuracy of street canyon temperature estimation is quantitatively analyzed with reference to the observation data of automatic weather stations and the simulation results of ENVI-met microclimate model.The main conclusions of this paper include:(1)The CTTC model is highly sensitive to the parameters ? and ? in the local-scale urban meteorological parameterization scheme(LUMPS).The change of the values of parameters ? and ? will lead to a great change in the results and accuracy of the model.Compared with sensible heat flux,the CTTC model is less affected by heat storage flux and has a low sensitivity to the parameters of OHM model.(2)The estimated results of CTTC model are consistent with the measured results of automatic weather stations over time.Their correlation coefficient is 0.97,the average absolute error is 0.92?,and the root mean square error is 1.19?.So the accuracy of the CTTC model is high.(3)The results of ENVI-met Urban Microclimate Simulation and the observation data of automatic weather station have the same temporal variation.The correlation coefficient between them is 0.93.The model simulation error is small and the accuracy is high.The spatial distribution of simulated temperature is consistent with the actual temperature distribution of the object type.Compared with ENVI-met simulation results,the estimated results of CTTC model are more correlated with the measured data,and the errors are concentrated between-2?~2?.The estimated errors of CTTC model are mainly distributed in the areas of dense buildings and main roads,and in the period of strong solar radiation,the estimated errors are larger.In the nighttime without solar radiation,the results of CTTC estimation and ENVI-met simulation are in good agreement with each other in spatial distribution.The difference of average temperature is 0.5 C,and the deviation is much lower than that of daytime.