Summer cooling island effects of blue-green spaces in severe cold regions: A case study of harbin, China

Blue-green spaces exhibit a cooling island effect in urban thermal environments. This study, through field measurements combined with thermal comfort indices and CFD simulations, explored the summer cooling island effect in micro-scale blue-green spaces of severe cold regions, summarizing the spatiotemporal characteristics of the effect. Measurements were conducted in Harbin at three water bodies of varying sizes and shapes, revealing a notable cooling island effect at a distance of 6–8 m from the water. The highest Mean Cooling Island Intensity (MCII) of 3.18 °C was recorded at 10 a.m. in a circular water body with compound vegetation. Furthermore, the combination of water bodies and vegetation proved more effective in reducing temperatures than single factors alone, with the peak coupling effect of 6.37 °C at 6 m from the water at 11 a.m. Thermal environment surveys determined Harbin's Neutral Universal Thermal Climate Index (UTCI) temperature range to be 13.3–25.06 °C. Additionally, modeling and optimization comparisons in ENVI-met confirmed that adding a small number of deciduous trees to grassland areas and altering the type of waterside platform can optimize the thermal environment. This research provides a solid foundation for the optimized design of blue-green spaces in severe cold regions.