  City-scale outdoor thermal comfort diagnostics are essential for
understanding actual heat stress. However, previous research primarily focused
on the street scale. Here, we present the WRF-UCM-SOLWEIG framework to achieve
fine-grained thermal comfort mapping at the city scale. The background climate
condition affecting thermal comfort is simulated by the Weather Research and
Forecasting (WRF) model coupled with the urban canopy model (UCM) at a
local-scale (500m). The most dominant factor, mean radiant temperature, is
simulated using the Solar and Longwave Environmental Irradiance Geometry
(SOLWEIG) model at the micro-scale (10m). The Universal Thermal Climate Index
(UTCI) is calculated based on the mean radiant temperature and local climate
parameters. The influence of different ground surface materials, buildings, and
tree canopies is simulated in the SOLWEIG model using integrated urban
morphological data. We applied this proposed framework to the city of
Guangzhou, China, and investigated the intra-day variation in the impact of
urban morphology during a heat wave period. Through statistical analysis, we
found that the elevation in UTCI is primarily attributed to the increase in the
fraction of impervious surface (ISF) during daytime, with a maximum correlation
coefficient of 0.80. Tree canopy cover has a persistent cooling effect during
the day. Implementing 40% of tree cover can reduce the daytime UTCI by 1.5 to
2.0 K. At nighttime, all urban features have a negligible contribution to
outdoor thermal comfort. Overall, the established framework provides essential
input data and references for studies and urban planners in the practice of
urban (micro)climate diagnostics and planning.
