Amplified Urban Heat Islands during Heat Wave Periods

Abstract

Heat waves and urban heat islands (UHIs) may interact together, but the dependence of their interaction on background climate is unclear. Hourly meteorological observations in June to August from 2013 to 2015 collected in the megacities of Beijing (temperate semihumid monsoon climate), Shanghai (subtropical humid monsoon climate), and Guangzhou (marine subtropical monsoon climate) in China were used to study the interaction. At each megacity, eight rural stations and eight urban stations, respectively, were selected to study the UHI. Although under different background climates, UHIs in Beijing and Guangzhou shared a similar diurnal variability, that is, higher in the nighttime. However, the diurnal cycle is opposite for Shanghai if rural coastal stations were selected as rural reference stations. During heat wave periods, daytime (10:00–16:00) UHIs were intensified by 0.9 ± 0.13 (mean ± 1 standard deviation) °C in Shanghai, nighttime (22:00–4:00) UHIs were intensified by 0.9 ± 0.36 and 0.8 ± 0.20 °C in Beijing and Guangzhou, respectively. The surface solar radiation during the heat wave period was approximately 1.5 times to that under normal conditions in each city. The enhanced solar radiation during heat waves, which was absorbed by the urban canopy in the daytime and released at night, was closely related to nighttime UHIs in Beijing and Guangzhou and daytime UHIs in Shanghai. Additionally, changes in wind direction were observed in Shanghai under heat waves, that is, with more than 63% (wind direction) of the wind originating from neighboring hot cities in the southwest instead of the cool sea breeze from the southeast, which led to a significant increase in daytime UHIs during heat wave periods.

Heatwaves and Summer Urban Heat Islands: A Daily Cycle Approach to Unveil the Urban Thermal Signal Changes in Lisbon, Portugal

“…Although a positive interaction between UHIs and heat waves has been demonstrated in several regions, different results were also observed in cities under different local background climates. Previous examples of positive interactions between HW and the UHI effect have been found in Atlanta [18], Athens [13], Beijing, Guangzhou and Shanghai [56], and Paris [29]. In the first study, meteorological data from three stations (one urban, one hybrid and one rural) were used, covering the 1984 to 2007 period, and a 1.0 • C UHI intensity increase was detected between HW and non-HW days.…”

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

“…Anthropogenic heat flux is closely related to the change in built-up area around the stations (Figure 1B). Therefore, anthropogenic heat flux can be considered to reliably reflect the effects of both anthropogenic emissions and land-use change related to latent heat flux and sensible heat flux (Jiang et al, 2019;Chen et al, 2020). Therefore, classified the stations by the mean anthropogenic heat fluxes around all the stations.…”

A New Evaluation of the Role of Urbanization to Warming at Various Spatial Scales: Evidence From the Guangdong‐Hong Kong‐Macau Region, China

“…The Guangdong‐Hong Kong‐Macau region (GHMR, Figure 1a), especially the Greater Bay Area (GBA), is a typical region of China's economic development and most rapid urbanization. Thus, the urbanization effect on climate change in this region has been of great concern to scientists and the public (J. Y. Huang et al, 2004; Jiang et al, 2019; Q. X. Li et al, 2004; Luo & Lau, 2017; Ye et al, 2018; Zhou et al, 2004). Since there are no sufficient rural stations that can be used as a climate reference in this region, especially in the recent past, it is difficult in studying the contribution of urbanization to the warming and its uncertainty.…”