Impact of Changes in Blue and Green Spaces on the Spatiotemporal Evolution of the Urban Heat Island Effect in Ningbo and Its Implications for Sustainable Development

Blue and green spaces (BGS) play a crucial role in mitigating the urban heat island (UHI) effect by not only lowering land surface temperature (LST) but also regulating the urban microclimate and enhancing ecosystem services. In this study, Ningbo City is selected as the research area. LST data for the years 2014, 2017, 2020, and 2023 were retrieved using Landsat 8 imagery processed via the Google Earth Engine platform, employing an atmospheric correction approach. Simultaneously, land use types were classified using the random forest algorithm. Based on these datasets, a Geographically and Temporally Weighted Regression model was employed to quantitatively assess the spatial and temporal impacts of BGS changes on the UHI effect. The results reveal that (1) from 2014 to 2023, BGS in Ningbo exhibited a consistent decline, while construction land expanded significantly, leading to a gradual increase in the annual average LST; (2) strong UHI zones were primarily concentrated in urbanized zones and closely aligned with regions of elevated LST; the minimum, maximum, and average LST values in blue and green spaces were significantly lower than those observed in cultivated land and construction land; (3) the variation in the influence coefficient of blue space on LST was greater than that of green space, suggesting stronger spatiotemporal heterogeneity in its regulatory effect on the urban thermal environment. Additionally, the green-to-blue space area ratio increased from 9.7:1 in 2014 to 12.8:1 in 2023, deviating progressively from the optimal ecological balance. To promote sustainable urban development, it is imperative for Ningbo to strengthen the conservation and restoration of BGS, optimize their spatial configuration through evidence-based planning, and ensure the long-term stability of ecological functions.