Synergistic Response of Blue and Green Spaces as Urban Cooling Source to Extreme Heatwaves

Extreme heat events (EHEs), intensified by climate change, threaten urban sustainability and public health. Blue–green spaces (BGSs) offer synergistic cooling potential to mitigate urban heat, yet their combined effects at medium scales remain understudied. Using Landsat-8 remote sensing imagery from the summer of 2022 and land use data for the same year, we retrieved land surface temperature (LST) in Fuzhou City, China, and developed an evaluation index system to quantify the collaborative cooling characteristics of blue–green spaces (BGSs) across 89 research units. Regression analysis was then applied to examine the relationship between the spatial distribution of BGSs and their cooling effects. Key findings reveal the following: (1) the area of blue–green spaces is the most critical factor affecting the cooling intensity; (2) increasing the proportion of green space would yield a more pronounced cooling effect than expanding the blue space; (3) increasing blue space would grow the contribution of higher cooling amplitude and distance, but cooling efficiency would decrease accordingly; and (4) the seamless integration of blue–green spaces along the coastline can significantly amplify their synergistic cooling effect. This study has implications for addressing the synergistic cooling effects of blue and green spaces to improve the resistance of urban ecosystems to climate change-induced environmental stress and extreme heatwaves.