Scaling, optimisation, and application of vegetation canopy radiative transfer model at microclimate scale

Urban greenery is widely recognised as a strategy to mitigate urban overheating, and its shading capacity is crucial for improving microclimate and thermal comfort. Nevertheless, research on modelling the vegetation canopy radiation transfer (VCRT) process for the microscale is lacking, and most existing VCRT models are taken out from mesoscale models. In this study, we used canopy morphology and structure as an entry point to construct a VCRT model for the microscale, from the mesoscale model. Firstly, 100 m and 1000 m were defined as the critical scales by scaling, and the effect of leaf distribution on VCRT was analysed. The VCRT model was made applicable to the microscale by introducing a scattered radiation source term and 6 leaf inclination distribution (LID) functions, and the results showed that the proposed model could improve the accuracy of canopy radiation absorptivity by about 11%. In addition, both leaf area index (LAI) and LID had significant effects on VCRT, and vegetation with LAI above 2 and spreading leaves had better shading effects. It is worth noting that urban greenery has an exciting potential for thermal comfort improvement, with the potential to regulate even extremely hot weather from near "very hot" (148 W/m²) to almost "comfortable" (69 W/m²). This study is a catalyst for improving the predictability of the VCRT process for microclimate and thermal comfort, providing theoretical support and implications for mitigating urban overheating and enhancing urban thermal resilience.