Authors:
Yun Yee Soh, Yijun Lu, Ziyuan Zhang, Marcel Ignatius, and Nyuk Hien Wong
Department of Built Environment, National University of Singapore, Singapore.
Abstract
Urban vegetation has gained significant recognition as an effective measure for mitigating heat, particularly in tropical cities. Understanding how it influences ambient temperatures is therefore essential for designing thermally comfortable urban environments. To achieve this, various methods are employed to quantify greenery. This study investigates greenery metrics that best explain and predict microclimatic temperature variations and identifies the temporal scale that provides the most robust understanding of temperature dynamics. Using the National University of Singapore (NUS) campus as a living laboratory, air temperature data were collected from 12 weather stations at 10-minute intervals and aggregated into daily, monthly, and yearly averages for maximum (Tmax), minimum (Tmin), daytime (Tday), and nighttime (Tnight) temperatures. Greenery and urban morphology metrics were derived from LiDAR-based 3D data and monthly street view imagery indices.
Generalised Additive Models (GAMs) and Principal Component Analysis (PCA) were applied to evaluate the relationships between greenery metrics and temperature measures while addressing collinearity among highly correlated variables. Results show that the explanatory power (R²) of greenery metrics varies across temperature measures and temporal scales. Metrics describing daily temperature fluctuations capture only a small portion of the variability influenced by short-term temporal factors. In contrast, monthly aggregation smooths transient effects, and yearly aggregation provides a more accurate interpretation as structural factors such as vegetation volume and built density become more dominant. The exploratory findings establish distinct metrics for understanding greenery across contexts, from extreme heat mitigation to daily thermal performance, and offer valuable insights for landscape design and the development of a standardized tree-planting evaluation system in dense tropical environments.
Keywords:
Urban Heat Mitigation, Ambient Air Temperature Variability, Urban Vegetation, Urban Morphology