An Observational Case Study of Synergies between an Intense Heat Wave and the Urban Heat Island in Beijing

Abstract

The focus of this study is an intense heat episode that occurred on 9–13 July 2017 in Beijing, China, that resulted in severe impacts on natural and human variables, including record-setting daily electricity consumption levels. This event was observed and analyzed with a suite of local and mesoscale instruments, including a high-density automated weather station network, soil moisture sensors, and ground-based vertical instruments (e.g., a wind profiler, a ceilometer, and three radiometers) situated in and around the city, as well as electric power consumption data and analysis data from the U.S. National Centers for Environmental Prediction. The results show that the heat wave originated from dry adiabatic warming induced by the dynamic downslope and synoptic subsidence. The conditions were aggravated by the increased air humidity during subsequent days, which resulted in historically high records of the heat index (i.e., an index representing the apparent temperature that incorporates both air temperature and moisture). The increased thermal energy and decreased boundary layer height resulted in a highly energized urban boundary layer. The differences between urban and rural thermal conditions throughout almost the entire boundary layer were enhanced during the heat wave, and the canopy-layer urban heat island intensity (UHII) reached up to 8°C at a central urban station at 2300 local standard time 10 July. A double-peak pattern in the diurnal cycle of UHIIs occurred during the heat wave and differed from the single-peak pattern of the decadal average UHII cycles. Different spatial distributions of UHII values occurred during the day and night.

Urban Heat Island and Its Interaction with Heatwaves: A Review of Studies on Mesoscale

“…In contrast to the in situ measurement, thermal infrared remote sensing from satellites allows global monitoring of geophysical parameters such as land surface temperature, and thus is widely used for studying surface urban heat island [51,52]. A few studies [29,53] also used ground-based or aircraft-based remote sensors to observe the urban boundary layer (UBL). Among the various satellite images, Moderate Resolution Imaging Spectroradiometer (MODIS) (https://modis.gsfc.nasa.gov, accessed on 6 June 2021) and Landsat (https://landsat.gsfc.nasa.gov, accessed on 6 June 2021) images are commonly used [54][55][56][57][58][59].…”

“…On the other hand, HWs may strongly affect the spatial and temporal variability of UHI by altering sensible and latent heat transfer and changing wind conditions [4,27,28]. While many researchers [27][28][29] have reported synergistic interactions between UHI and HW, other researchers [25,30] found no synergistic effect. Nevertheless, the interaction between UHI and HW is complex and remains a subject of debate.…”

Changing structures of summertime heatwaves over China during 1961–2017

“…Cloud cover and surface humidity generally increased through the entire heatwave periods, resulting in hot days occurring ahead of hot nights. A case study suggested that the sources of the increased moisture included both local evaporation and moisture advection (An et al, 2020). Future studies will investigate the relevant mechan-isms involving the roles of land-atmosphere processes and atmospheric circulations.…”

Impacts of Continuously Increasing Urbanization Ratios on Warming Rates and Temperature Extremes Observed Over the Beijing Area

“…This phenomenon can be attributed to differences in urbanization ratios. A high urbanization ratio leads to a stronger nighttime UHI during hot nights, which is related to the synergistic interaction between UHI and heat waves (An et al., 2020; Ao et al., 2019; Jiang et al., 2019; D. Li & Bou‐Zeid, 2013). This study proved that this synergy also exists at stations far away from the main urban area but have high urbanization ratios.…”