Unraveling the effects of extreme heat conditions on urban heat environment: Insights from local climate zones and integrated temperature data

Abstract

Rapid urbanization and increasing human activities pose significant challenges to urban climates, particularly the urban heat island (UHI) effect, with UHI intensity (UHII) exacerbated by more frequent extreme heat events. Local climate zone (LCZ) provides insights into urban thermal environments but lacks high-accuracy LCZ maps and studies on the extreme heat impacts in non-metropolitan cities. Additionally, gaps exist in understanding how extreme daytime and nighttime heat conditions affect urban heat when integrating seamless near-surface air temperature (NSAT) and land surface temperature (LST) data. To address these gaps, we propose a high-accuracy LCZ mapping framework for the Guanzhong Plain urban agglomeration (GPUA) in China. By combining the LCZ map with 1-km gridded NSAT and LST data derived from machine learning methods, we comprehensively analyze extreme heat effects on surface UHII (SUHII) and canopy UHII (CUHII) at the LCZ scale, considering daytime and nighttime conditions. We also discuss the impacts of changes in radiation fluxes and wind speed associated with extreme heat on UHII. Our findings reveal that: (a) The proposed framework provides an LCZ map over GPUA with an accuracy of 0.84. The maximum RMSE of daytime and nighttime NSAT are 1.73 °C and 1.93 °C, while the maximum RMSE of daytime and nighttime LST are 1.95 °C and 4.20 °C. (b) Extreme heat amplifies NSAT and LST disparities among LCZs, intensifying CUHII and SUHII more during the daytime than at nighttime, although nighttime extreme heat can lower CUHII and SUHII in certain built LCZs. (c) Higher daytime UHII under extreme heat correlates with increased differences in downward longwave radiation between built LCZs and LCZ D. These insights aid in mitigating urban heat risks and guide policymakers and urban planners.