Influence of urbanization on radiative forcing in Beijing

Different forcing factors in urban areas contribute to the radiative forcing values. In the present
work, GLASS albedo and CERES surface short wave radiation data were used to calculate the surface radiative
forcing due to changes in the surface albedo over the past 10 years in Beijing. Spatial distribution of radiative
forcing and statistical characteristics were investigated. Urban fringe area was extracted from Globel and 30
 Land Use and Land Cover Change data. Combination with calculated radiative forcing of remote sensing data
enabled extraction of radiative forcing values for urban district, inner zone and all levels in the outer edge
region. Relationship between land cover change driving factors and climate-driving factors was explored. It has
been found that over the past ten years, the radiative forcing in the whole of Beijing region was 2.52 W·m^-2,
leading to a temperature increase. The average value of radiative forcing in land cover-unchanged region was
found to be 2.26W·m^-2, accounting for 89% of all the radiative forcing in the whole region. Of such changes,
cultivated land and wood land were the two major radiative forcing sources. The average value of radiative
forcing in land-cover-changed region was found to be 0.26 W·m^-2. The non-vegetation land cover change
contributed 0.09W·m^-2, while vegetation-including-land-cover change generated radiative forcing of 0.18 W·
m^-2. In the city core area, radiation forcing was found to be -1.16 W·m^-2, exhibiting as a cooling effect.
The radiative forcing change was correlated to the distance away from urban district, first increasing and then
decreasing from inside to outside. The present work provides a typical study of radiation forcing in urban areas,
and data obtained would be helpful to understand differences in regional climate in Beijing.