Tree planting indices and their effects on summer park thermal environment: A case study of a subtropical satellite city, China

Urban residents are suffering from serious thermal stress resulting from urban heat island and global warming. Investigators have explored several methods to address this issue. Vegetation, especially trees, were found to play a vital part in urban environments. It produces a cooling effect by reducing temperature and radiation levels. To find thermal performances of trees in detail, this study physically measured two urban parks during August 2019 in a satellite city of China regarding their thermal environments relevant to tree planting indices. There were three planting indices used, sky view factor, leaf area index and enclosure area. Through associating them with thermal indicators by linear regression, all of the indices were confirmed to have significant thermal effects. Every 0.1 increase in sky view factor resulted in an increase of 1 degrees C air temperature, 0.16 m/s air velocity, 40 W/m(2) solar radiation level and 1.6 degrees C mean radiant temperature. Same effects were found in nearly 0.4 leaf area index decrease and approximately 20 m(2) enclosure area increase. These results provide very optimistic directions for future urban forestry planning and landscaping.