Spatial Variability and Temporal Heterogeneity of Surface Urban Heat Island Patterns and the Suitability of Local Climate Zones for Land Surface Temperature Characterization

Ziqi Zhao,Xin Dong,Ayyoob Sharifi,Bao-Jie He,Lidu Shen

doi:10.3390/rs13214338

Abstract

This study investigated monthly variations of surface urban heat island intensity (SUHII) and the applicability of the local climate zones (LCZ) scheme for land surface temperature (LST) differentiation within three spatial contexts, including urban, rural and their combination, in Shenyang, China, a city with a monsoon-influenced humid continental climate. The monthly SUHII and LST of Shenyang were obtained through 12 LST images, with one in each month (within the period between 2018 and 2020), retrieved from the Thermal InfraRed Sensor (TIRS) 10 in Landsat 8 based on a split window algorithm. Non-parametric analysis of Kruskal-Wallis H test and a multiple pairwise comparison were adopted to investigate the monthly LST differentiations with LCZs. Overall, the SUHII and the applicability of the LCZ scheme exhibited spatiotemporal variations. July and August were the two months when Shenyang underwent strong heat island effects. Shenyang underwent a longer period of cool than heat island effects, occurring from November to May. June and October were the transition months of cool–heat and heat–cool island phenomena, respectively. The SUHII analysis was dependent on the definition of urban and rural boundaries, where a smaller rural buffering zone resulted in a weaker SUHI or surface urban cool island (SUCI) phenomenon and a larger urban area corresponded to a weaker SUHI or SUCI phenomenon as well. The LST of LCZs did not follow a fixed order, where in July and August, the LCZ-10 (Heavy industry) had the highest mean LST, followed by LCZ-2 (Compact midrise) and then LCZ-7 (Lightweight low-rise). In comparison, LCZ-7, LCZ-8 (Large low-rise) and LCZ-9 (Sparsely built) had the highest LST from October to May. The LST of LCZs varied with urban and rural contexts, where LCZ-7, LCZ-8 and LCZ -10 were the three built LCZs that had the highest LST within urban context, while LCZ-2, LCZ-3 (Compact low-rise), LCZ-8, LCZ-9 and LCZ-10 were the five built LCZs that had the highest LST within rural context. The suitability of the LCZ scheme for temperature differentiation varied with the month, where from July to October, the LCZ scheme had the strongest capability and in May, it had the weakest capability. Urban context also made a difference to the suitability, where compared with the whole study area (the combination of urban and rural areas), the suitability of built LCZs in either urban or rural contexts weakened. Moreover, the built LCZs had a higher level of suitability in an urban context compared with a rural context, while the land-cover LCZs within rural had a higher level of suitability.

Highlights

Cities are already the main human settlements since global urban population exceeded rural population in 2007, and about 68% of the world population is projected to live in cities by 2050 [1]
Our results indicate that such a hypothesis was not applicable to the case study city of Shenyang, where the surface urban heat island intensity (SUHII) based on a 100% buffering zone was 0.13–0.16 ◦ C higher than that based on a 50% buffering zone in July and August
An accurate quantification of urban thermal environments is the premise of mitigating and avoiding the several consequences of urban heat challenges which are experienced by many cities

Summary

Introduction

Cities are already the main human settlements since global urban population exceeded rural population in 2007, and about 68% of the world population is projected to live in cities by 2050 [1]. The increasing urbanization trend has brought a variety of challenges to cities, such as urban climate change, limited access to open and public spaces, low-quality housing conditions and constrained access to public transport [2]. One of the most acknowledged urban climate change phenomena is the urban heat island (UHI) effect, referring to the fact that cities are warmer than their surrounding suburban or rural areas [3,4]. The heat-induced impacts can be more severe because of the interaction of UHI and heat waves that are getting more frequent, longer and more severe along with global warming [10,11]

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Conclusion