The characteristics of urban heat island variation in Beijing urban area and its impact factors

The relationships among urban heat island (UHI) distribution and landcover categories, topographic factor, vegetation greenness, and surface evapotranspiration are analyzed in Beijing urban area in 2001. The results show that the significant UHI occurs in Beijing urban area in the four seasons. The land surface temperature (LST) difference is approximately 4-6degC between Beijing city and suburb areas, comparatively is 8-10degC between Beijing city area and outer suburbs area in northwestern region in summer time. The UHI spatial distribution is corresponding with the urban geometry structure profile. The UHI in nighttime is obvious than that in daytime in Beijing city area. And in the daytime, the significant UHI mainly appears in the summer. The evapotranspiration in suburb area is larger than that in urban area in the summer, and significantly high latent heat exchange leads to LST difference between city and suburb area. The reflection of surface landcover categories is sensitive to the UHI, and the scatterplot shows that there is the negative correlation between NDVI and LST (R² = 0.6481). It indicates that the vegetation greenness is a key factor for reducing the UHI, and large-scale construction of greenbelt can considerably reduce the UHI effect.