基于Landsat-8影像的沿海城市公园冷岛效应——以厦门为例

城市公园主要由水体和绿色植被等景观构成，其形成的公园冷岛（Park cool island，PCI）已成为减缓城市热岛效应的重要途径之一。采用景感生态学中的景感营造理念规划设计城市公园或优化公园空间结构有助于增强公园冷岛效应，进一步改善局地城市热环境。选择沿海城市——厦门市为研究对象，基于2013年8月的Landsat-8 OLI/TIRS遥感影像和Google Earth高分影像数据，首先提取了研究区15个公园的土地利用信息，采用改进的地表温度单通道算法，获取了城市公园地表温度数据，并采用缓冲区分析、景观格局指数和多元统计等方法定量分析公园内部平均地表温度、城市公园冷岛强度（即降温幅度）、公园冷岛影响距离（即对周边区域的降温范围）三者的主要影响因子，并利用景感生态学原理初步剖析了城市公园景感营造的原则。结果显示：（1）公园面积和公园建设用地面积是影响公园平均温度的关键因子（R²=0.915），这两个因子与公园平均温度均呈显著非线性相关；公园面积存在阈值55 hm²左右；（2）公园冷岛PCI强度由公园绿地面积、公园建筑面积和面积-周长形状指数（P/A）三个因子决定（R²=0.911）；公园冷岛PCI强度与公园绿地面积呈显著非线性正相关，与公园建筑面积呈显著非线性负相关，与面积-周长形状指数（P/A）呈显著线性负相关；在确保公园绿地面积达到一定阈值时，应该尽量降低公园建筑面积，增加公园形状复杂度，有利于其PCI强度的增加，缓解城市热岛效应；（3）公园冷岛影响距离由公园面积和公园水体面积比例决定（R²=0.719），公园冷岛影响距离与两者呈显著正相关；绿地公园中提高公园水体的面积比例，有助于增大公园冷岛的影响距离；（4）城市公园的规划与设计，需要运用景感生态学的原理，从缓解城市热岛效应的角度，充分考虑公园大小、形状、土地利用类型组成比例及空间配置等因素。

Quantifying the cool-island effects of urban parks using Landsat-8 imagery in a coastal city, Xiamen, China

Urban parks mainly consist of green space and water, which can form park cool islands (PCIs), which substantially alleviate the urban heat island effect. The concept of landsense creation in landsenses ecology can facilitate the rational planning of new urban parks and the optimization of the spatial structure of parks, which help to enhance PCIs and improve the local urban thermal environment. Xiamen, a coastal city in China, was taken as a case study. Landsat-8 Operational Land Imager/Thermal Infrared Sensor imagery data from August 2013 were acquired. A land use type map with a total of 15 urban parks was derived from high-spatial-resolution Google Earth images. Land surface temperature was estimated via an improved single-channel algorithm. Methods including buffer analysis, the landscape pattern index, and multivariate regression were applied to evaluate the key factors of average surface temperature of parks, PCI intensity (i.e., the cooling amplitude), and effective cooling length (L_max). Additionally, based on the concept of landsenses ecology, landsense principles for the creation of urban parks were proposed. The results indicate the following: (1) average temperature (AvT) inside the parks depends on the park size and built-up land area, and both of these factors are non-linearly correlated to AvT (R²=0.915). The threshold value of the park size is approximately 55 hm²; (2) The PCI intensity is mainly determined by the area of green space, the built-up land area inside the park, and the park perimeter-area ratio (PAR). Green space area has a positive impact on PCI intensity, however, the built-up land area and PAR have a negative impact on PCI intensity (R² = 0.911). On the premium of keeping a certain park green space area, it is critical to reduce the built-up area and increase the complexity of the geometric shape of the parks, which is conducive to increasing their PCI intensity and alleviating the urban heat island effect; (3) L_max is mainly determined by park size and the percentage of water area, and both of these factors have a positive impact on L_max (R² = 0.719). On the premium of maintaining a certain park area, it is proposed to enhance the proportion of water bodies in the parks, which helps to increase the L_max value of urban parks; and (4) in the planning and design of urban parks, the concept of landsenses ecology could be employed to consider park size, land use types, the shape index, and the spatial configuration inside the parks to mitigate urban heat island effects.