Study On Temporal And Spatial Distribution Of Anthropogenic Heat In The Main Urban Area Of Xi'an City

Anthropogenic heat is produced by human activities and released into the atmosphere in the form of sensible heat and latent heat,which is one of the important energy sources of urban ecosystem.Anthropogenic heat not only affects urban climate,hydrology,water resources and air quality,but also affects the health and living comfort of urban residents,which restricts the improvement of people's living quality and the sustainable development of cities.Due to the acceleration of urbanization and population explosion,as the important factor of urban heat island,anthropogenic heat has become increasingly unable to ignore.Therefore,in order to better understand the anthropogenic heat emission and its influence on the urban thermal environment,the spatial and temporal distribution of anthropogenic heat in the main urban area of Xi'an were studied.In this study,the six main urban areas of Xi'an(Weiyang District,Baqiao District,Yanta District,Beilin District,Lianhu District,and Xincheng District)was taken as the research object,remote sensing parameters such as NDVI,MNDWI,surface albedo and surface emissitivity were calculated using Landsat TM and Landsat OLI/TIRS images on June 4,2011,August 15,2014,June 17,2016,and August 10,2018.Based on this,land use classification and inversion of land surface temperature in Xi'an were completed.The net surface radiation,sensible heat flux,latent heat flux and soil heat flux were calculated to obtain the anthropogenic heat flux,and then analyzed the spatial distribution images of anthropogenic heat flux.Based on the statistical data of Xi'an Statistical Yearbook from 2000 to 2018,and the anthropogenic heat released by human metabolism,industry,transportation and life were taken into account in the calculation,the temporal variation characteristics of anthropogenic heat were studied.The main conclusions are as follows:(1)The surface temperature in the main urban area of Xi'an is generally higher in the city center and lower in the surrounding suburbs.Among them,the surface temperature of water is the lowest,and the surface temperature of built-up area shows a higher level.In areas with higher vegetation coverage such as woodlands,grasslands and parks surface temperatures shows lower levels.(2)The spatial distribution of anthropogenic heat is generally dispersed,higher in the northern part of the city than in the southern part,and the anthropogenic heat emission gradually expands to the north.Anthropogenic heat is mainly distributed in densely populated areas,especially in railway stations.The heat flux is larger in densely built residential areas and prosperous business districts.Industrial areas also have higher level because of their higher energy consumption.(3)The total anthropogenic heat emission in the main urban area of Xi'an has been increasing year by year,from 0.94×10¹⁶J in 2000 to 4.99×10¹⁶J in 2018,and the average emission flux has increased from 15.85 W/m²to 21.83 W/m².However,the growth rate has slowed down.From the perspective of multi-year average,industry,transportation,life and human metabolism account for 36.2%,38.6%,13.5%and11.7%of the total emissions of the four sources.Industrial activities,transportation and large population are the main sources of anthropogenic heat.(4)The anthropogenic heat emission has obvious diurnal variation characteristics.The concentration period of anthropogenic heat emission is from 8:00 to 20:00.During this period,people have frequent activities,heavy traffic and large industrial energy emissions.After 20:00,anthropogenic heat emission is small and gradually decreases with time,and the anthropogenic heat reaches the lowest value around 4:00.(5)In general,the spatial and temporal distribution difference of anthropogenic heat in the main urban area of Xi'an is closely related to the changes of social and economic factors,energy consumption,macro policies and land use structure.