Examining supply and demand of cooling effect of blue and green spaces in mitigating urban heat island effects: A case study of the Fujian Delta urban agglomeration (FDUA), China

Blue and green spaces (BGSs) are used as the important resource to mitigate urban heat island (UHI) effect through their cooling effect. However, research on the supply and demand of cooling effect of BGSs is limited. This study used the Fujian Delta urban agglomeration of China as the study area. Based on multi-source data, we constructed the evaluation indicator system to quantify the supply capacity of cooling effect (CESC) and the demand level of cooling effect (CEDL), and revealed the law of spatial distribution and changes in the CESC and the CEDL. Moreover, we further analyzed the correlation, matching state and coupling coordination degree (CCD) between the CESC and the CEDL. The results showed that (1) in the study area, the CESC has a spatial distribution with a decreasing gradient from the inland BGSs with high elevations to the coastal urban areas, while the CEDL exists the opposite trend. The CESC is negatively correlated with the CEDL, and there is a clear spatial spillover effect. (2) The matching state between the CESC and the CEDL exhibits obvious polarization. An increasing number of areas might face shortage of cooling effect supply. (3) The CCD between the CESC and the CEDL is in a state of low coordination level. In eastern coastal urban areas, the incoordination of the CESC and the CEDL become serious increasingly. (4) In areas with 'low supply-high demand' and incoordination, the intensity of urban construction and the size of population should be controlled, and the BGSs should be improved to enhance the CESC. Meanwhile, in areas with 'high supply-low demand' and incoordination, spatial structure of land-use/land-cover should be optimized to improve the efficiency of cooling effect utilization. This research can provide a new perspective and scientific basis for the BGSs layout in order to achieve the mitigation of UHI effect.