[1] In this study, an analysis of long-term rainfall data reveals that the rapid urban expansion in Beijing since 1981 is statistically correlated to summer rainfall reduction in the northeast areas of Beijing from 1981 to 2005. This coincides with the period in which the shortage of water in the Beijing area has become a serious factor for sustainable economic development. Meanwhile, an analysis of the aerosol optical depth (AOD) from the Total Ozone Mapping Spectrometer spanning the years from 1980 to 2001 shows that there is no clear secular trend in summer AOD in Beijing. With the particular purpose of further understanding the effects of urban expansion on summer rainfall and the potential measures to mitigate such effects, a mesoscale weather/land-surface/urbancoupled model along with different urban land-use change scenarios are used to conduct numerical simulations for two selected heavy summer rainfall events with different, but representative, summer weather patterns in Beijing. Results show that urban expansion can produce less evaporation, higher surface temperatures, larger sensible heat fluxes, and a deeper boundary layer. This leads to less water vapor, more mixing of water vapor in the boundary layer, and hence less (more) convective available potential energy (convective inhibition energy). The combination of these factors induced by expanding urban surfaces is helpful in reducing precipitation for the Beijing area in general and, in particular, for the Miyun reservoir area (the major source for the local water supply). Increasing green vegetation coverage in the Beijing area would produce more rainfall, and model results show that planting grass seems more effective than planting trees. For the same vegetation, the rainfall difference from simulations using two green-planting layouts (annular and cuneiform) is small.

Urban greening helps cooling and humidifying the air; shading provided by buildings also affects outdoor thermal environment. Therefore, they both influence the thermal perceptions of people in outdoor spaces. The sky view factor (SVF) is a commonly used parameter in the research on urban climate, indicates the relationship between the visible area of the sky and the area covered by urban structures. The current paper first gives a brief introduction of the SVF and fisheye imagery. It then describes a method conducted to estimate SVF for urban environment analysis by using fisheye lenses and applying the ENVI platform as well. Finally, micro-climate characteristics over three typical urban underlying surfaces, including sunlit asphalt roads, shaded roads by building and by chinars were analyzed based on on-site observations. For a high-density city such as Nanjing, the present study reveals that the higher building shaded, chinar canopy density, and the lower sky transmittance, humidification and cooling of the air is more significant under the same climate condition and the same road. For benefiting urban environmental planning and assessment in high-density cities, more cases simulation with different combinations of factors are needed, which can provide a set of better greening guides and the optimal shading level.