Human-oriented urbanization and related land-use change processes significantly affect the thermal environment of cities and their surrounding areas by transforming the natural landscape into an impervious surface [1
]. The most prominent urban thermal environment problem is the development of urban heat islands (UHIs). As one of the most obvious characteristics of urban climate change caused by construction and human activity, UHIs constitute heat accumulation in urban areas due to their higher surface temperature compared with the surrounding suburbs and rural regions [4
]. By changing the structure and function of the ecosystem and terrestrial surface energy exchange processes, UHIs proceed to negatively affect the urban climate and urban hydrology [6
]. UHIs also seriously threaten the suitability of urban living environments and the health of residents [8
]. With the continuing advance of urbanization, the scale and intensity of UHIs will become more and more serious. Therefore, it is of practical importance to understand how urbanization influences the UHI effect and microclimates, for future planning, ecological protection, and sustainable development in these areas.
While urbanization can promote developmental changes that improve people’s living standards, it can also lead to increasingly serious UHI effects. To understand more fully the mechanism and characteristics of urbanization on UHIs, many studies have analyzed the relationship between urbanization and land surface temperature (LST) [11
]. These related studies have focused on the spatiotemporal characteristics and influencing factors of UHIs [17
]. For example, based on MODIS 8-day composite LST products, the differences in surface urban heat island intensity (SUHII) among seasons and cities, and between day and night, were analyzed in the Yangtze River Delta urban agglomeration; the specific impact of climatic factors (e.g., precipitation, air temperature, solar radiation, and wind speed) and urbanization factors (build-up intensity, population density, and urban area size) on SUHII were further analyzed using Pearson’s correlation coefficients and stepwise linear regression [21
]. Additionally, there has been great interest in simulations of UHI spatial patterns [22
] and the interaction between UHIs and the landscape pattern under urbanization [24
]. Most of the existing research has concentrated on and is limited to the impact of urban expansion on UHIs. However, as an important component of urbanization, few studies have considered how urban renewal influences UHIs and the urban microclimate.
Inefficient urban land use and insufficient land reserves are inevitable with urbanization. As such, rapid urban sprawl tends to accompany urban renewal [27
], i.e., the demolition and/or renovation of old industrial, commercial, and residential areas and urban villages, to improve the vitality of the area and its relationship with the surrounding environment [29
]. For example, some urban villages, old factories, and polluting facilities can be rebuilt as residential, office, commercial, or leisure complexes. Abandoned houses and shanty towns may be modernized or removed to allow space for public facilities, such as green parks, markets, and parking lots. As urban renewal can be beneficial to land use efficiency and the environment by changing urban morphology and development patterns, it has gradually become a key focus in urban planning and urban sustainable development management [31
However, research on the influence of urban renewal on LST has been limited, with few studies published to date [32
]. For example, based on high-resolution Worldview images and multi-temporal Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) thermal infrared images, manually extracted urban renewal areas and LST change in the region have been investigated over different time periods [33
]; however, it is difficult to apply the analysis results widely as they typically depend on manual interpretation of optical satellite imagery, which is prone to adverse atmospheric conditions and cloud pollution [15
], and the expense of high-resolution Worldview images limits the wide usage of this method. Consequently, the resulting ground time series data may not be generally acquired and provide a good representation of actual conditions in different regions of interest.
Therefore, we established a more general framework to study LST changes caused by urban renewal integrating free and open dataset including optical images, radar images, and thermal infrared images. The main objectives of this study were: (1) to interpret automatically and obtain city urban renewal areas according to the integration of Landsat images and Advanced Land Observation Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) images; (2) to retrieve the LST from Landsat thermal infrared data over different periods; and (3) to analyze the impact of urban renewal on LST changes to provide a new perspective on the impact of urban renewal on microclimates.
Urban renewal is an effective method for solving shortages in urban land resources with urbanization by redeveloping land that is used inefficiently. At the same time, urban renewal affects the urban microclimate and is steadily receiving more attention. In this study, we proposed a general, flexible framework to determine how urban renewal processes influence LST, using multi-source remote sensing images. We presented a case study of core and peripheral regions in Guangzhou City, China, between 2007 and 2017 to analyze the spatial differences in different urbanized areas on the basis of urban renewal area identification and LST remote sensing inversion. Our results indicated that the urban renewal process is conducive to a decline in LST in core region districts with relatively high urbanization, whereas peripheral regions with relatively low urbanization presented the opposite characteristics. The outcomes can be explained by the joint influence of population density, building density, and landscape pattern changes in the process of urban renewal. It is our hope that the results from this study provide a new perspective on the impact of urban renewal on urban microclimates and thermal environmental changes to promote greater awareness of this issue in future planning and management practices.