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Abstract: The development of urban blue-green spaces is highly recommended as a nature-based solution for mitigating the urban heat island (UHI) phenomenon, improving urban sustainability, and enhancing resident well-being.Therefore, accurately and conveniently quantifying their cooling effect and mechanisms is crucial for effective urban spatial planning and high-quality development.In this study, Landsat 8 cloud-free images from the summer of 2021 were used to retrieve land surface temperature (LST) and related indices.Five evaluation methods, including the study area method (SAM), equal radius method (ERM), impervious surface method (IMM), maximum perspective method (MPM), and accumulative perspective method (APM), were applied to estimate the cooling intensity (CI) for a total of 375 green space, water body, and urban park patches in 25 cities within the Yangtze River Delta region.This study also explored the spatial characteristics and environmental impacts on CI.The results indicated that: (1) CI estimated by the five methods showed a significant correlation for most categories of blue-green spaces.All landscape categories exhibited a high correlation between IMM and ERM with MPM, while APM showed the highest correlation coefficient with MPM in green spaces and urban parks.(2) The cooling effects obtained by different estimation methods varied, with IMM presenting the highest average CI values, followed by MPM and ERM, while APM exhibited the lowest CI values.SAM demonstrated instability at the city scale.(3) Dominant factors influencing the cooling effect of different blue-green spaces exhibited significant differences.Green spaces were mainly influenced by internal vegetation coverage and human activities, water bodies displayed a relatively notable correlation with patch spatial characteristics, and the cooling capacity of urban parks was highly related to their surrounding environment.These findings are essential for city planners to understand the cooling effect in comparable urban contexts and provided scientific references for sustainable urban management.