Does the spatial pattern of urban blue-green space at city-level affects its cooling efficiency? Evidence from Yangtze River Economic Belt, China

Utilization of urban blue-green spaces had been recognized as an environmentally friendly and politically acceptable approach to mitigate global warming. However, the evidence and hence knowledge of how the spatial pattern of urban blue-green space at city-level affects its cooling efficiency are limited. Therefore, in this paper, we are devoted to clarifying the cooling mechanism of urban blue-green space from the perspective of composition and distribution pattern. To do that, the Yangtze River Economic Belt, which had experienced significant environmental deterioration and contained rich blue-green resources, was taken as the case study site. Besides, the panel regression models and a new quadratic-curve-fitting based threshold effect estimating model were constructed to investigate the impact of spatial pattern of blue-green space on its holistic cooling intensity at city-level and to estimate the optimal spatial layout of blue-green spaces with maximum cooling efficiency. The results evidenced that the proportion and distribution characteristics of forests and shrublands in urban areas improved the intensity of urban cold island effect significantly, while that of grassland and water bodies mitigated urban heat island effect. Moreover, it was demonstrated that the city-level spatial pattern of urban blue-green space has a greater influence on its cooling efficiency at specific time periods (summer and daytime) and regions (mountainous cities with a small population). In addition, it was estimated that the cooling effect reaches the local maximum (around 1.2 celcius) when the PLAND / LSI index of forests, shrublands, grasslands, and water bodies at city-level is about 20%, 0.1%, 42.5% and 15.4% / 38.25, 5.08, 48.25 and 8.54, respectively. We believe our findings contribute significantly to the understanding on the link between ecological land elements and sustainable development of urban ecosystem.