Evaluating the impact of tree species and formations on outdoor thermal comfort in urban environments : a case study of Glasgow

Abstract

Urban overheating already challenges pedestrian well-being in temperate-maritime cities such as Glasgow, where densely built corridors register up to 5 °C warmer than their rural surroundings. This dissertation evaluates how tree species and planting configurations can alleviate that heat, combining empirical measurements with micro-climate modelling. A GIS overlay of Local Climate Zones, NDVI and census population first delineated a high-density urban zone (Sauchiehall Street, LCZ 2) and a contrasting medium-density residential zone (Kelvin Way, LCZ 6/B) for detailed study. Five street tree species: C. betulus, A. campestre, G. biloba, Ulmus ‘New Horizon’ and Platanus × hispanica—were then monitored during five fair-weather summer afternoons. The field campaign informed the calibration of an ENVI-met model for Sauchiehall Street (RMSE = 0.76 °C), against which thirteen greening scenarios varying crown maturity, row number, spacing and alignment were tested.

Field data show that radiative control dominated thermal perception: C. betulus shade cut mean radiant temperature (MRT) by 8 °C and Physiological Equivalent Temperature (PET) by ≈ 3 °C, whereas sparsely pollarded London-plane crowns increased MRT by 8 °C and PET by 4 °C. Across species, PET rose almost linearly with SVF (r = 0.73), confirming crown density as the key cooling trait. Model experiments revealed that, merely allowing the existing single row to mature yielded < 2 °C PET relief, but adding a facing row at one-crown spacing halved SVF and lowered peak PET by ≈ 3 °C. Introducing a slender third row yielded a further ≈ 1 °C benefit, while tighter spacing or staggering rows offered only marginal gains (< 0.5 °C).

Synthesising measurement and modelling evidence, the thesis proposes six ‘cool-street rules’ for Glasgow streets. Implementing these guidelines could shift deep street canyons from moderate heat stress to no thermal stress classes on typical summer afternoons, securing climate-resilient, people-centred streetscapes for the city’s warming future.