The minimum distance for ecological security from perspective of the thermal environment: the case of three northern districts of Dalian

With the concept of "the minimum distance for ecological security" first proposed by The Ministry of Environmental Protection in 2014, the ecological safety within and between cities has been paid increasing attention to by society, while the minimum distance for ecological security based on the thermal environment has gradually become the focus of people′s attention. Based on the essential connotation of the minimum distance for ecological security from the perspective of thermal environment, combined with remote sensing image, administrative boundaries, and the boundaries of built-up areas, this paper uses the Gaussian mixture model and heat island signal function to calculate the area of the heat island and the minimum distance for ecological security in the three northern districts of Dalian from 2013 to 2014. The research shows that the total area of the urban heat island in the three northern districts of Dalian has expanded from 694.10 km~2 to 1864.30 km~2. At the same time, the minimum distance for ecological security between Pulandian and Wafangdian decreased from 8.70 km to-3.10 km, resulting in the superposition of thermal environment, which was relatively dangerous. However, the minimum distance for ecological security between Pulandian and Zhuanghe decreased from 73.47 km to 58.24 km, and the thermal environment did not appear to undergo superposition, which was relatively safe. Overall, the urban heat island area gradually expanded, and the minimum distance for ecological security between cities gradually decreased.