Effect and driving mechanisms of urban renewal on urban heat island mitigation in Beijing

Urban heat island mitigation (UHIM) is an important part of urban ecosystem services, playing a critical role in mitigating the urban heat island (UHI) effect and significantly affecting the urban habitat environment. Urban spatial evolution significantly affects UHIM. Numerous studies have been conducted on the effect of urban spatial evolution on UHIM, but most of the existing studies focus on the effect of urban incremental development on UHIM and neglect the significant role of urban renewal as a crucial means of urban stock development in this process. Taking the region within the Sixth Ring Road of Beijing as an example, we use multi-source remote sensing imagery to accurately identify the characteristics of regional urban renewal changes. Then, we use the spatial evaluation model of ecosystem services to quantify UHIM, and evaluate the effect of urban renewal on UHIM through a machine learning model. The results show that: (1) From 2015 to 2022, the urban renewal area in the region totaled 25,977.45 ha, accounting for 11.44 % of the total area of the region. Urban renewal within the region is characterized by large areas, multiple types, wide distribution, and high frequency. According to the change characteristics of urban functions and the degree of development, the urban renewal modes in the region include Built-up renewal, Eco-land adjustment, Eco-restoration, New construction and Clearance phase mode. (2) The UHIM in the region was overall relatively weak, locally extremely strong, and unevenly distributed. During the study period, the regional UHIM increased (the average value of the UHIM index increased by 0.02), with both gain and loss areas distributed outside the Fifth Ring Road of the region. (3) New construction and Eco-restoration mode had a greater impact on UHIM, with the former having a negative impact (average contribution: 0.063) and the latter having a positive impact (average contribution: 0.057). In terms of contribution, vegetation contributed the most to the effect of urban renewal on UHIM (average contribution: 0.070), and it was followed by the impervious surface (average contribution: 0.010). The former made a positive contribution, while the latter made a negative contribution. This study proposes corresponding optimal layout strategies based on contribution factors and urban suitability evaluation. These strategies serve as a basis for ecological construction in the process of urban renewal.