Diurnal dynamics of heat exposure in Xi'an: A perspective from local climate zone

Understanding the heat exposure in communities is important for finely managing the urban thermal environment. Although remote sensing data has been widely applied for evaluating heat exposure, rare studies discuss it by using diurnal land surface temperature (LST) at the block level, let alone integrating the local climate zone (LCZ) scheme. Therefore, we classified 716 urban blocks into 10 LCZ types and then combined them with the Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station LST data to investigate the diurnal spatio-temporal heterogeneity of heat exposure. First, we found that surface urban heat island intensity (SUHII) reached the maximum value of 2.3 °C at noon. Compact built-up LCZs were heat islands over the day, while the open and dispersed built-up LCZs had greater uncertainties. Specifically, LCZ 4 and LCZ 9 can be cold or heat islands over the day. Second, the distribution characteristics of SUHII was highly consistent with that of heat exposure levels, i.e., high SUHII zones have high heat exposure level. Third, the heat exposure intensity levels among compact building zones (LCZ 1–LCZ 3) had a reverse change during daytime and nighttime and the same phenomenon was observed among open building zones (LCZ 4–LCZ 6). Our results implied that LCZ 3 and LCZ 2 should be given more priority to alleviate heat exposure risks than other built-up LCZs.