Synergistic Influence of Local Climate Zones and Wind Speeds on the Urban Heat Island and Heat Waves in the Megacity of Beijing, China

Abstract

Large-scale modifications to urban underlying surfaces owing to rapid urbanization have led to stronger urban heat island (UHI) effects and more frequent urban heat wave (HW) events. Based on observations of automatic weather stations in Beijing during the summers of 2014–2020, we studied the interaction between HW events and the UHI effect. Results showed that the UHI intensity (UHII) was significantly aggravated (by 0.55°C) during HW periods compared to non-heat wave (NHW) periods. Considering the strong impact of unfavorable weather conditions and altered land use on the urban thermal environment, we evaluated the modulation of HW events and the UHI effect by wind speed and local climatic zones (LCZs). Wind speeds in urban areas were weakened due to the obstruction of dense high-rise buildings, which favored the occurrence of HW events. In detail, 35 HW events occurred over the LCZ1 of a dense high-rise building area under low wind speed conditions, which was much higher than that in other LCZ types and under high wind speed conditions (< 30 HW events). The latent heat flux in rural areas has increased more due to the presence of sufficient water availability and more vegetation, while the increase in heat flux in urban areas is mainly in the form of sensible heat flux, resulting in stronger UHI effect during HW periods. Compared to NHW periods, lower boundary layer and wind speed in the HW events weakened the convective mixing of air, further expanding the temperature gap between urban and rural areas. Note that LCZP type with its high-density vegetation and water bodies in the urban park area generally exhibited, was found to have a mitigating effect on the UHI, whilst at the same time increasing the frequency and duration of HW events during HW periods. Synergies between HWs and the UHI amplify both the spatial and temporal coverage of high-temperature events, which in turn exposes urban residents to additional heat stress and seriously threatens their health. The findings have important implications for HWs and UHII forecasts, as well as for scientific guidance on decision-making to improve the thermal environment and to adjust the energy structure.

Synergies between Urban Heat Island and Urban Heat Wave Effects in 9 Global Mega-Regions from 2003 to 2020

“…In addition, when taking the four types of climate zones among the mega-regions: (1) Humid subtropical (YRD, PRD, Tokyo, Boston, Mexico City, São Paulo); (2) Tropical rainforest (Jakarta); (3) Marine west coast climate (Paris); (4) Desert climate (Nile), into consideration, we observed some patterns potentially associated with climatic conditions. For example, the mega-regions in the humid subtropics more often exhibit stronger UHI intensity (LST difference between built-up and Non-built-up areas) [91,92]. In contrast, thanks to the moderating effect of the ocean [93], the difference between thermal environments of built-up and Non-built-up areas is less evident.…”

Dual Effects of Synoptic Weather Patterns and Urbanization on Summer Diurnal Temperature Range in an Urban Agglomeration of East China

“…The intensification of urbanization across the globe has also contributed to the decline in DTR since the 1950s (Gallo et al, 1996;Kalnay and Cai, 2003;Feddema 2005;Mohan and Kandya, 2015). This is mainly because the underlying impervious surfaces of cities increases the nighttime temperature by absorbing a large amount of energy in the daytime and releasing it at night (Forster and Solomon, 2003;Zhou et al, 2007;Yang et al, 2020a;Zong et al, 2021). At the same time, due to the radiative cooling effect of aerosol pollution over cities, the daytime temperature decreases (Zheng et al, 2018;Yang et al, 2020b), and ultimately the DTR decreases in cities owing to the asymmetry in the changes of maximum and minimum temperature.…”

Comment on amt-2021-301

“…This shows that built-up areas and human influence were spreading from the city center to the surrounding areas during this period. However, the intensity and range of the CUHI did not increase with this trend, because the wind field and weather background have a stronger influence on CUHI than urbanization (Hong et al, 2018;Zong et al, 2021).…”

“…In addition to global climate change, the influence of human activities on the CUHI cannot be ignored. Previous studies have pointed out that AHF is closely related to the change in built-up areas and population density around the stations, which reflects the fact that the effects from both anthropogenic emissions and land-use change are related to latent heat flux and sensible heat flux (Zhou et al, 2012;Yang et al, 2020b;Wang et al, 2020a;Zhang et al, 2021). Therefore, AHF was retrieved via a physical method (Bing Chen and Shi, 2012;Chen et al, 2012;Chen et al, 2014) based on 1000-m spatial resolution NOAA nighttime lighting data and with local economic development and energy consumption data, and the AHF data at the same time in Nanjing were provided by Chen et al (Bing Chen and Shi, 2012;Chen et al, 2012;Chen et al, 2014)…”

“…Human activities and urbanization have a significant impact on the spatial distribution of UHI (Shahmohamadi et al, 2011;Zhang et al, 2015;Li et al, 2020;Zong et al, 2021). To explore this influence, concentric rings with various radii (5 km, 10 km, 15 km, ..., 40 km) were created surrounding the city center.…”