Canyon geometry and the nocturnal urban heat island: Comparison of scale model and field observations

TLDR

Thermal admittance differences can produce realistic heat island features, but their magnitude needs field quantification. The study investigates how rural/urban differences in canyon geometry and thermal admittance influence nocturnal urban heat islands, emphasizing canyon geometry as a key urban design feature. A simple hardware scale model simulates nocturnal cooling rates for rural and urban settings under calm, cloudless conditions to explore these effects. The model reproduces observed urban heat island development and long‑wave radiative exchange, showing that sky‑view‑factor–based canyon geometry drives nocturnal heat islands and links city size to heat‑island intensity.

Abstract

Abstract A simple hardware scale model is used to simulate nocturnal cooling rates for rural and urban environments under calm and cloudless conditions. Comparison with field observations gathered under similar conditions shows the model capable of reproducing many of the features of the temporal development of urban heat islands and the long‐wave radiative exchange in urban canyons. The model is used to investigate the roles played by rural/urban differences in geometry and thermal admittance. The results of the experiments show that canyon geometry in the central portion of a city (as measured by the sky view factor) is a relevant variable in producing nocturnal urban heat islands due to its role in regulating long‐wave radiative heat loss. It is also demonstrated that this measure is central to the relationship between city size and heat island intensity. The importance of canyon geometry as a feature of urban design is discussed. Thermal admittance differences can also produce realistic heat island features but their magnitude requires quantification in the field.