Increasing Heat Stress in Urban Areas of Eastern China: Acceleration by Urbanization

Abstract

A combination of hot temperature and high humidity (high heat stress) has severe impacts on environment, society, and public health, especially in urban areas where the majority of the world's population lives. This study investigates the changes of heat stress in urban areas of eastern China and urbanization effects. Data for 242 urban areas and records from a dense network of nearly 2,000 stations are examined. All urban areas have experienced substantial increases in mean heat stress and the frequencies of extreme heat stress days and events during 1971–2014. The increases in human‐perceived heat stress are even stronger than air temperature. Urban areas experience more intense heat stress than the surrounding rural areas. We estimate that urbanization accounts for nearly 30% of the increase in mean and extreme heat stress. Urbanization effects are more prominent in the major urban conglomerates such as Beijing‐Tianjin‐Hebei and the Yangtze and Pearl river deltas.

Urban Expansion and Drying Climate in an Urban Agglomeration of East China

“…YRDUA is one of the most densely populated and urbanized areas of the world. Intense urban development in this area has also considerably enhanced the UHI intensity (Du et al, 2016;Gu et al, 2011;Luo & Lau, 2018;Sun et al, 2016), which is usually defined as the difference in surface temperature between urban area and other types such as cropland, water, and rural area (Chen et al, 2006;Jin et al, 2005;Tomlinson et al, 2012;Zhou et al, 2013;Zhou et al, 2014). Although YRDUA occupies only 2.2% of China's land areas, it has a population of 0.15 billion and contributes to 18.5% of China's gross domestic product (National Development and Reform Commission of China, 2016).…”

“…The urbanization effect (UE) is then defined as the difference between the urban trend (Trend urban ) and the rural trend (Trend rural ): UE = Trend urban − Trend rural , and its relative contribution in percentage is given by UE Trendurban ×100% (Luo & Lau, 2018;Ren & Zhou, 2014). The urbanization effect (UE) is then defined as the difference between the urban trend (Trend urban ) and the rural trend (Trend rural ): UE = Trend urban − Trend rural , and its relative contribution in percentage is given by UE Trendurban ×100% (Luo & Lau, 2018;Ren & Zhou, 2014).…”

“…Urban land expansion is associated with urban population growth, economic development, and other regional or local factors such as land use policies, capital flows, and transportation costs (Bren d'Amour et al, 2017;Seto et al, 2011). Urbanization enhances sensible heat flux and soil heat flux at the expense of latent heat flux, thereby leading to the well-known urban heat island (UHI) effect (Jones et al, 2008;Luo & Lau, 2018;Yao et al, 2019;Zhou et al, 2004), with higher temperature in the urban core area than the surrounding rural areas (Kalnay & Cai, 2003;Oke, 1982;Zhao et al, 2018). Urbanization enhances sensible heat flux and soil heat flux at the expense of latent heat flux, thereby leading to the well-known urban heat island (UHI) effect (Jones et al, 2008;Luo & Lau, 2018;Yao et al, 2019;Zhou et al, 2004), with higher temperature in the urban core area than the surrounding rural areas (Kalnay & Cai, 2003;Oke, 1982;Zhao et al, 2018).…”

Greening in Rural Areas Increases the Surface Urban Heat Island Intensity

“…The urban areas in 2016 can include old and new urban areas due to urbanization. The reasons for selecting 10-to 30-km buffers are as follows: (1) The extents of SUHI and urbanization are generally greater than urban area size (Zhang et al, 2004;Zhou et al, 2015); thus, the buffer zones were not set near the urban areas; and (2) to reduce uncertainties caused by different climate conditions, the buffer zones were not set farther (Luo & Lau, 2018;Zhou et al, 2015). Cities with urban area size larger than 200 km 2 were analyzed; thus, a total of 397 cities were investigated (Table S1).…”

“…It can bring many adverse effects to human and environment (e.g., increasing mortality and energy consumption, and affecting water and air quality), thus receiving increasingly attention globally (Cao et al, 2018;Grimm et al, 2008;Luo & Lau, 2018;McCarthy et al, 2010). It can bring many adverse effects to human and environment (e.g., increasing mortality and energy consumption, and affecting water and air quality), thus receiving increasingly attention globally (Cao et al, 2018;Grimm et al, 2008;Luo & Lau, 2018;McCarthy et al, 2010).…”