Heat Stress Calculations within Urban Street Canyons Using Weather and Climate Model Variables

Oral Presentation

Quantifying human thermal comfort has been a topic of research for many years and provides more 
representative indicators of how the human body is coping with current weather conditions than 
temperature alone. This is specifically important in urban areas, where a growing percentage of the 
global population live, and where heatwave conditions tend to have greater impacts given their 
propensity for warmer conditions compared to surrounding areas via urban heat islands.

For both weather and climate services, therefore, there is a need to estimate thermal comfort in 
urban areas. The aim of this work is to develop a method to diagnose thermal comfort using 
variables that are included in standard output from weather and climate models, hence there is a 
need for computational efficiency. Methods exist to this end, but they typically either use a flat 
plane morphology (just considering incident radiation from the ground and the sky), or a street 
canyon morphology with numerical processing to treat the multiple reflections.

In this work, we present a new analytical approach to determine wet bulb globe temperature 
(WBGT) in an infinite street canyon. We present a complete set of equations that describe the mean 
radiant temperature experienced by a black globe located anywhere within a canyon, accounting for 
longwave, direct shortwave and diffuse shortwave, allowing up to two reflections off the canyon 
facets. We then demonstrate the behaviour of our approach across a range of plausible building 
geometries before evaluating it using observations and more detailed radiative transfer simulations.