Abstract
Due to global warming and human activities, heat stress (HS) has become a frequent extreme weather event around the world, especially in megacities. This study aims to quantify the responses of urban HS (UHS) to anthropogenic heat (AH) emission and its antrophogenic sensible heat (ASH)/anthropogenic latent heat (ALH) components and increase in the size of cities in the south and north China for the 2019 summer based on observations and numerical simulations. AH release could aggravate UHS drastically, producing maximal increment in moist entropy (an effective HS metric) above 1 and 2 K over the south and north high-density urban regions mainly through ALH. In contrast, future urban expansion leads to an increase in HS coverage, and it has a larger impact on UHS intensity change (6 and 2 K in south and north China) relative to AH. The city radius of 60 km is a possible threshold to plan to city sprawl. Above that city size, the HS intensity change due to urban expansion tends to slow down in the north and inhibit in the south, and about one-third of the urban regions might be hit by extreme heat stress (EHS), reaching maximal hit ratio. Furthermore, changes in warmest EHS events are more associated with high humidity change responses, irrespective of cities being in the north or south of China, which support the idea that humidity change is the primary driving factor of EHS occurrence. The results of this study serve for effective urban planning and future decision making.
Highlights
In the context of global warming, the probability, intensity, and duration of heat stress (HS) have been increasing around the world (Lee and Min, 2018; Wang et al, 2020), especially in megacities
The driving factors [e.g., natural factors, such as high temperatures, humidity, and solar radiation, and human activities, such as urban heat island (UHI) effect, anthropogenic heat (AH), etc.] and physical mechanisms are very different among regions (Seneviratne et al, 2012; Fischer and Knutti, 2013; Ohashi et al, 2014; Steinweg and Gutowski, 2015; Lee and Min, 2018; Lorenz et al, 2019)
HS change is determined by the coaction of temperature and humidity changes, which further increases the complexity of HS variation
Summary
In the context of global warming, the probability, intensity, and duration of heat stress (HS) have been increasing around the world (Lee and Min, 2018; Wang et al, 2020), especially in megacities. Different from a common heat wave with high temperature, heat stress is characterized as being an extremely hot and humid environment, and it is known in China as “sauna weather”. Region-scale studies are fundamentally required to project future changes in extreme events and to assess the dependence of HS or EHS on temperature and humidity changes (Napoli et al, 2019; Lutsko, 2021)
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