Landscape and Urban Planning 96 (2010) 224–231 Contents lists available at ScienceDirect Landscape and Urban Planning journal homepage: www.elsevier.com/locate/landurbplan Quantifying the cool island intensity of urban parks using ASTER and IKONOS data Xin Cao a,b , Akio Onishi b , Jin Chen a,∗ , Hidefumi Imura b a State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, Xinjiekouwai Street 19, Beijing 100875, China b Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan article info Article history: Received 18 April 2009 Received in revised form 18 March 2010 Accepted 21 March 2010 Available online 14 April 2010 Keywords: Park cool island Land surface temperature Land use Shape ASTER IKONOS abstract Urban parks can help mitigate urban heat island (UHI) effects and decrease cooling energy consumption in summer. However, it is unclear how park characteristics affect the formation of a park cool island (PCI). In this study, PCI intensity values for 92 parks in Nagoya, Japan were obtained from ASTER land surface temperature (LST) products and then correlated to detailed and use information derived from high-spatial-resolution IKONOS satellite data. The results indicate that (1) the cooling effect depends on the park size and seasonal radiation condition, and park size is non-linearly correlated to PCI intensity; (2) PCI intensity is mainly determined by the area of tree and shrub inside the park as well as the park shape, and grass has negative impact on PCI formation. The park vegetation and shape index (PVSI) proposed here well predicted PCI intensity of selected parks. These findings can help urban planners to understand PCI formation and design cool parks to counteract UHI effects. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The urban heat island (UHI) can lead to urban temperatures being 2–5 ◦ C higher than those in rural surroundings (Oke, 1973; Ackerman, 1985; Taha, 1997). Higher temperatures in urban areas not only accelerate urban smog formation and affect the inhabit- ability of cities (Mihalakakou et al., 2004), they also greatly increase cooling energy consumption in summer, contributing to global warming (Kolokotroni et al., 2007). Estimates for major US cities have shown that once temperatures exceed 15–20 ◦ C, a 1 ◦ C incre- ment will increase peak electricity demand by 2–4%. Thus the additional cooling energy consumption caused by a UHI is responsi- ble for 5–10% of electricity demand (Akbari et al., 1992). With rapid urbanization and accelerating global warming, UHI is of increasing public concern and strategies to mitigate UHI effects are needed both for energy-savings and urban-planning applications (Chang et al., 2007). Many field-based measurements have found that urban parks are 1–2 ◦ C, and sometimes even 5–7 ◦ C, cooler than their urban surroundings, forming a “park cool island” (PCI) (Jauregui, 1990; Spronken-Smith and Oke, 1998; Upmanis et al., 1998; Chang et al., 2007; Jusuf et al., 2007). Through advection caused by differ- ences in surface and air temperatures between the cooler park and its warmer built-up surroundings, the park cooling effect can ∗ Corresponding author. Tel.: +86 10 13522889711. E-mail addresses: caoxin@bnu.edu.cn (X. Cao), onishi@corot.nuac.nagoya-u.ac.jp (A. Onishi), chenjin@ires.cn (J. Chen), imura@genv.nagoya-u.ac.jp (H. Imura). extend beyond the park by the park’s width or even farther. A stronger PCI affects a more extensive area, resulting in lower cool- ing energy consumption in buildings around the park (Jauregui, 1990; Spronken-Smith and Oke, 1998; Ca et al., 1998; Eliasson and Upmanis, 2000). Considerable research efforts have been made to reveal which park characteristics are crucial to PCI formation. Pre- vious studies have found that larger parks have stronger PCI effects (Spronken-Smith and Oke, 1998; Upmanis et al., 1998), but the relationship between PCI effect and park size might be non-linear (Chang et al., 2007). Shashua-Bar and Hoffman (2000) reported that the tree-shaded area was a significant factor for the cooling effect, while Saaroni and Ziv (2003) found that water ponds in the park contributed to park cooling. Different park types or vegeta- tion combinations have also been discussed, but quantifiable effects and statistical relationships have not been established (Spronken- Smith and Oke, 1998; Chang et al., 2007), only with confirmation that vegetation lowers neighborhood temperatures by shading and by absorbing and converting ambient heat to latent heat through evapotranspiration. The above park characteristics are essential for urban planning and global change studies. However, the relationship between PCI intensity and park characteristics, especially in regard to detailed land cover/land use in a park, is not yet fully understood and thus limits the design of optimal parks for significant UHI miti- gation (Chang et al., 2007). Compared with in situ air temperature measurement, remote sensing provides not only the detailed land cover/land-use information, but also the land surface temperature (LST) observation with a more complete and uniform sampling. Considering the strong relationship between LST and air temper- 0169-2046/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.landurbplan.2010.03.008