Performance of tree canopy cover in mitigating future extreme heat across local climate zones: A case study of Guangzhou

Urbanization and climate change intensify urban heat and extreme heat events, threatening outdoor thermal comfort and health. However, existing studies have mainly focused on present day climates or typical summer conditions, while the responses of outdoor heat stress and the effectiveness of greening strategies across residential communities representing different LCZ types under future extreme heat wave scenarios remain less explored. This study assesses future changes in outdoor heat stress and the mitigation potential of tree canopy cover (TCC) in three residential communities in Guangzhou, China, representing Local Climate Zone (LCZ) 2 (compact mid-rise), LCZ1 (compact high-rise), and LCZ4 (open high-rise). ENVI-met simulations were conducted for five TCC levels (0–80%) under a typical meteorological day and four future scenarios (2050/2080, RCP2.6/RCP8.5), supported by on-site observations. Results show that the mean Physiological Equivalent Temperature (PET) increases from 50.3 °C (Typical Meteorological Day) to 51.1 °C in 2050 and 53.1 °C in 2080, while the extreme heat stress (EHS) proportion calculated from 09:00 to 18:00 rises from 43.3% to 42.7% and 58.3%. Among the three communities, LCZ2 shows the greatest deterioration, with EHS increasing from 22% (2050, RCP2.6) to 72% (2080, RCP8.5). Increasing TCC reduces PET and EHS overall, with an average PET decrease of 0.84 °C per 20% TCC, but the incremental benefit diminishes at high canopy cover; in the open high-rise community, PET rebounds and EHS increases when TCC exceeds 60%. These findings reveal morphology dependent and non linear greening effectiveness under future climate scenarios, providing practical guidance for optimizing tree canopy design to reduce extreme heat risks in residential areas.

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