Performance of Hong Kong's common trees species for outdoor temperature regulation, thermal comfort and energy saving

In comparison with the reference case (no trees), results revealed a reduction in maximum temperature of 0.4 °C and 0.5-1.0 °C under the current and 30% GCR situations respectively; and a decrease in average Physiological Equivalent Temperature of 1.6 °C and 3.3-5.0 °C. The area coverage of “Very Hot” thermal sensation reduced from ∼60% in the reference case to ∼50% with the current GCR and 17-21% with 30% GCR. Lastly, a decrease in cooling energy of 1500 kWh per typical summer day was observed with the current GCR, which increased to ∼1900-3000 kWh with 30% GCR, equivalent to 200-450 US$ savings within the 500 × 500 m2 domain. The variations in the estimated benefits between the 30% GCR scenarios reflect the importance of species-specific analysis. Statistical analysis revealed leaf area index was the main driver of the observed benefits, followed by trunk height, tree height and crown diameter. Our findings will encourage city planners and citizens to take actions for urban greening.