Urban Cooling Island Dynamics During the Development of an Ecological Urban Agglomeration in China

Ecological urban agglomeration in China face increasing pressure to reconcile rapid urban expansion with the maintenance of blue-green spaces (BGSs) that sustain urban cooling island (UCI) effects. While existing research has documented UCI dynamics in mature cities, an important unresolved issue remains in understanding how rapid urbanisation reshapes BGS patterns and weakens their cooling capacity in newly developing ecological urban agglomeration. Here, using multi-source remote sensing data, Markov land transition analysis, and Weather Research and Forecasting simulations, we investigated the spatiotemporal dynamics of BGSs and their thermal effects in a representative ecological urban agglomeration in eastern China during 2000–2020. We found that historical land-cover change in the study area was characterised not only by the expansion of development land from 7.18% to 13.55%, but also by the transition and spatial reorganisation of blue-green spaces, accompanied by declining BGS continuity and increasing ecological fragmentation. Thermal analyses further showed that water and wetlands consistently provided the strongest cooling effects, whereas developed land and bare land were associated with higher relative land surface temperature. Transitions to water and wetland generally produced stronger cooling effects than most other land-cover transitions; however, the cooling performance of newly converted ecological land remained weaker than that of long-established natural BGSs. In the representative city of Huai’an, simulated temperature patterns also showed that connected blue-green structures were associated with relatively stronger local cooling during the analyzed high-temperature period. Together, these findings indicate that rapid urbanisation not only changes BGS patterns but is also associated with weakened cooling performance and greater thermal pressure across the regional landscape. Preserving existing high-quality BGSs, especially water and wetlands, and improving the spatial configuration and connectivity of urban blue-green systems are therefore essential for climate-adaptive planning in rapidly developing ecological urban agglomeration.