The effects of sky view factor on ground surface temperature in cold regions - A case from Xi'an, China

Integrated implementation of spatial and climate information is important for urban thermal environmental optimization. Sky view factor (SVF) is an urban form evaluation index widely used to study the relationship between geometrical parameters and microclimate characteristics. This relationship depends on the climate condition and the time scale of the study. We studied the influence of SVF on microclimate of typical high-rise street canyons of Xi'an in winter and conducted comparative simulations based on different street canyon geometries, which calculated hourly ground surface temperature (GST). We used 2 kinds of method to establish the correlation between SVF and GST -the statistical regression and physical model regression. With the statistical regression, we found a significant negative correlation coefficient of -0.87 between SVF and nighttime GST and a positive correlation coefficient of 0.53 between the SVF and daytime GST. The results based on physical model regression, however, showed that an increase of 0.1 in SVF caused daytime GST drops by 0.06 degrees C-0.49 degrees C. Whether separating the change in direct solar radiation levels accompanied by the changes in SVF was the main factor that leads to the difference in determine the relationship between SVF and daytime GST under the two methods. For the environment with large shadow fraction (SF), such as high-rise street canyons, we recommend the physical model regression as the regression mechanism between SVF and GST. Results of this study can be used in environmental urban planning standards.