Study On The Surface Heat Flux Inversion And The Urban Thermal Environment In Nanjing Based On The SEBAL Model

In recent years, with the intensification of urban heat island effect and the rapid development of urbanization, the expansion of urban area, urban thermal environment is deteriorating, which affect the urban sustainable development. To understand the forming mechanism of urban thermal environment, reduce the urban heat island effect, and improve the living quality. This paper took Nanjing (excluded LiShui,Gaochun, and Liuhe) as an example, with remote sensing data, digital elevation data, and meteorological data as data sources. First, we conducted the inversion of parameters on the energy balance equation, analyzed interannual variability, seasonal variation, and spatial change with the SEBAL model, and compared with research results with literature. Second, we analyzed temporal and spatial variation on the evolution of urban thermal environment, and put forward some suggestions to improve the urban thermal environment. Finally, we analyzed the change rule of urban thermal environment from energy balance. The results showed that:(1) Net radiation flux and soil heat flux in Nanjing was spring> summer> winter. Sensible heat flux was close to the surface temperature; warm season (spring and summer) was greater than cold seasons (autumn and winter). The latent heat flux was the maximum in summer, the minimum in winter, spring and autumn was in the middle, and this mainly depended on the vegetation coverage, growth condition, and water conditions.(2) The space distribution of net radiation flux in Nanjing was Yangtze river> lakes> forest land>>farmland> grassland>old cities> bare land> new town, soil heat flux was Yangtze river> lakes> old cities> new cities> bare land> farmland> grassland> forest land, sensible heat flux was new cities> old cities> forest land> bare land> farmland> grassland> lakes> Yangtze river, and latent heat flux was Yangtze river> lakes> forest land> grassland> farmland> bare land> old cities> new cities, This were consistent with the spatial distribution of land use types. The average Bowen was spring> autumn and winter> summer. The Bowen of different land use types was new cities> old cities> bare land> forest land> farmland> grassland> lakes> Yangtze River.(3) There was a close relationship between urban thermal field level and underlying surface land use types in Nanjing, the thermal field took the largest area in medium temperature and low temperature area, a larger area in high temperature and low temperature, a smaller area in high temperature, and the smallest area in highest temperature in Nanjing from 1985 to 2014. The area was gradually increasing with the urban development in medium high temperature area; high temperature area rose was the most obvious. Overall, urban thermal field level gradually transformed from medium and low temperature to medium and high temperature. The thermal field level of water and forest land would improve with the urban cold island in winter, the urban internal thermal field level and the surrounding land use type was not obvious in winter.(4) By comparing the energy balance equation parameters and the urban thermal field level, the results showed that, as urban thermal field level dropped, net radiation flux and latent heat flux presented obvious rising trend; soil heat flux, sensible heat flux presented obvious downward trend. As for the season, the difference of energy balance equation parameter between adjacent heat field intensity was spring and summer> autumn> winter. The difference of energy balance equation parameter between adjacent heat field level presented the most obvious in the highest temperature high temperature area.