Cooling effects of green areas are an effective way to mitigate the urban higher temperature caused by urban heat islands. The cooling extent goes beyond a green area’s boundary and extends into its surrounding area. However, measurement of the exact cooling extent and mechanism of such effects had remained unclear. Using Landsat Enhanced Thematic Mapper Plus (ETM+) images of Beijing, we have determined the lower temperature of green cooled areas by land surface temperature, identified green areas’ cooling extents, and evaluated the relation of cooling extents to green areas’ features. Results show that the total size of extended cooled areas is larger than that of total green areas, and the cooling extents and magnitudes are statistically related to the biomass, size and shape of green areas. This study has demonstrated the calculation of cooling extents, and provided an approach to the assessment of cooling effects.

Cities in China have developed rapidly since economic reform. Meanwhile, mass incidents have happened more frequently. The annual growth rate of mass incidents has exceeded that rate of urban population growth and mass incidents have become a serious threaten to further urbanization in China. We first analyse the reason of rapid growth number of mass incidents, then point out that job supplement will trigger severer mass incidents and the development mode of sacrificing environment for economic growth will incur more mass incidents, both of which will be obstacles for China’s urbanization. Therefore we suggest that Chinese government should implement institution reform to overcome these obstacles.