Enhancing Microclimate Sustainability: The Impact of Blue–Green–Gray Underlying Surfaces in Stormwater Parks Under Subtropical Monsoon Climates

As a type of green stormwater infrastructure (GSI), stormwater parks play a crucial role in mitigating urban heat and managing stormwater, especially in subtropical monsoon climates where high temperatures and rainfall coincide. The benefits of microclimate improvement are associated with the specific surface types of stormwater parks. However, research on how different surfaces affect the microclimates of stormwater parks remains limited. This study utilized an unmanned aerial vehicle to investigate the surface temperature characteristics of blue–green–gray underlying surfaces within a stormwater park and employed multiple linear regression to analyze their impact on the microclimate. The results indicated that (1) blue underlying surfaces functioned as a stable cold source in dry periods but warmed quickly after rainfall. (2) Green surfaces consistently provided a cooling effect on the microclimate, with cooling intensity intricately related to vegetation structure. Specifically, the cooling effects of arbor–shrub–grass and arbor–shrub combinations were greater than those of other plant configurations. (3) The warming effect of gray underlying surfaces was affected by weather conditions and permeability, with pervious concrete exhibiting lower surface temperatures than impervious pavements during dry spells, although this difference diminished significantly after rain. These findings provide scientific evidence and design guidance for enhancing the sustainability of microclimates.