A Multi-timescale Study Of The Urban Thermal Environment In Beijing

In the 21st century,the world has entered into a process of rapid urbanization,which has led to a qualitative transformation of the subsurface and the concentration of energy use in urban areas as a result of the massive concentration of population in these areas,and these factors interact to produce the unique environmental phenomenon of the urban heat island effect.The urban heat island effect can have a series of negative effects and seriously affect human health and quality of life as well as the sustainable development of society.Starting from the theory of landscape ecology and local climate zones(LCZ),this paper focuses on the land use cover changes in Beijing over the past 30 years,the influence of landscape pattern on the urban thermal environment at annual time scale,the method of constructing local climate zoning maps using multi-source data,and the analysis of thermal environment similarity of different LCZ types at monthly time scale.The main research results and conclusions obtained are as follows:(1)Annual-scale thermal environment analysis of Beijing based on landscape pattern.The random forest algorithm was used to classify the land cover of Beijing in 1990,2004 and2019,and the overall classification accuracy was verified to be around 90%.The surface temperature was later obtained by inversion of the radiative transfer equation method,and the mean temperature of land cover types was tested to be significantly different,and the mean temperature of buildings and bare ground was higher than that of green space and water bodies;and the spatial distribution map of landscape pattern of built-up areas and green areas was calculated by combining with the moving window algorithm.The analysis reveals that the landscape index of built-up areas and green spaces has a significant effect on the surface temperature LST and there is a significant regularity in the time series,which indicates that a reasonable improvement of urban landscape distribution can alleviate the urban thermal environment.(2)A method for constructing local climate zones based on multi-source data.A standardized process for constructing local climate zoning using multiple sources of data is explored,which starts from the definition of LCZ and uses multiple surface morphological parameters to overcome the problems of blurred boundaries,inefficiency and low accuracy in the original LCZ classification,and has better generalizability.By selecting Google Earth sample images of each LCZ type,3D street view reference and conducting field photo survey,the overall classification accuracy of LCZ is 84.9% and the Kappa coefficient is 0.83.(3)Monthly-scale thermal environment analysis of Beijing based on local climate zones.Based on the LCZ classification map to analyze the temperature distribution of LCZ in different months,it reveals that there are similarities and differences in the temperature characteristics of LCZ categories,and there are strong regularities in different months;At the same time,using one-way variance with Tukey HSD post hoc test,it was found that more than 90% of LCZ pairs had significant differences in temperature,thus verifying the feasibility of using LCZ to study LST;finally,using the promoted heat island intensity calculation method for local climate zones,the heat island intensities of different months in Beijing were calculated,and the analysis found that there was a strong regularity in the heat island intensities of different months and The analysis reveals that there is a strong pattern of heat island intensity in different months and reveals the heat effect of different LCZ types.