Understanding the impact of heatwave on urban heat in greater Sydney: Temporal surface energy budget change with land types

Jing Kong; Yongling Zhao; Dominik Strebel; Kai Gao; Jan Carmeliet; Chengwang Lei

doi:10.1016/j.scitotenv.2023.166374

Understanding the impact of heatwave on urban heat in greater Sydney: Temporal surface energy budget change with land types

Sci Total Environ. 2023 Dec 10:903:166374. doi: 10.1016/j.scitotenv.2023.166374. Epub 2023 Aug 26.

Authors

Jing Kong¹, Yongling Zhao², Dominik Strebel², Kai Gao³, Jan Carmeliet², Chengwang Lei⁴

Affiliations

¹ Centre for Wind, Waves and Water, School of Civil Engineering, The University of Sydney, Sydney, Australia. Electronic address: jkon4926@uni.sydney.edu.au.
² Department of Mechanical and Process Engineering, ETH Zürich, Zürich, Switzerland.
³ Institute of Future Cities, Chinese University of Hong Kong, Hong Kong, China.
⁴ Centre for Wind, Waves and Water, School of Civil Engineering, The University of Sydney, Sydney, Australia.

PMID: 37640068
DOI: 10.1016/j.scitotenv.2023.166374

Abstract

The impact of heatwaves (HWs) on urban heat island (UHI) is a contentious topic with contradictory research findings. A comprehensive understanding of the response of urban and rural areas to HWs, considering the underlying cause of surface energy budget changes, remains elusive. This study attempts to address this gap by investigating a 2020 HW event in the Greater Sydney Area using the Advanced Weather Research and Forecasting (WRF) model with 250-m high resolution. Findings indicate that the HW intensifies the nighttime surface UHI by approximately 4 °C. An analysis of surface energy budgets reveals that urban areas store more heat during the HW due to receiving more solar radiation and less evapotranspiration compared to rural areas. The maximum heat storage flux in urban during the HW can be around 200 W/m² higher than that during post-HW. The stored heat is released at nightime, raising the air temperature in the urban areas. Forests and savannas have relatively lower storage heat fluxes due to high transpiration and albedo, and the maximum heat storage flux is only around 50 W/m² higher than that during post-HW. In contrast, a negative synergistic effect is detected between the 2-m UHI and HW. This may be because other meteorological conditions including wind have substantial impacts on the air temperature pattern. The strong hot and dry winds coming from the west resulted in a higher air temperature in the western urban district, and intra-city disparities are higher. Meanwhile, the western forest area also experiences higher temperatures due to the westward winds. In addition, changes in wind direction alter the temperature distribution in the northern rural region. The findings of the present study may provide some insights into urban heat mitigation during HW.

Keywords: Heatwave (HW); Intra-city disparity; Surface energy budget; Urban heat island (UHI); WRF.