## 1 Introduction  
The urban heat island (UHI) effect is a representative microclimate phenomenon that has resulted from urbanization, leading to higher temperatures in central urban areas than in suburban areas [1]. The effect causes social problems in cities that can be attributed to high temperatures, including increased energy demand and a greater incidence of heat-related illnesses. In particular, heatwaves caused by global warming and subsequent climate change are combining with the UHI effect to exacerbate health risks for urban residents [2]. The United States Environmental Protection Agency has proposed heat island cooling strategies (HICSs) to solve problems caused by the UHI effect [3]. These strategies involve planting trees and vegetation; installing green roofs, cool roofs, and cool pavements; and implementing smart growth [3]. Various national and local governments are currently using HICS to reduce UHIs [3; 4; 5]. The World Health Organization (WHO) has specified that areas in which the abovementioned techniques are used, including the planting of vegetation and trees and the development of green roofs in cities, should be regarded as urban green spaces (UGSs). These measures will improve the quality of urban environments, which tend to trap more heat than natural environments [6]. The Intergovernmental Panel on Climate Change (IPCC) collectively refers to cool roofs and cool pavement techniques as ground-based albedo modification (GBAM); it promotes GBAM as an important approach for reducing high temperatures in urban areas [7]. Both bodies indicate that these measures are necessary for adaptation to climate change. The measures described above utilize three mechanisms to lower temperatures. First, UGSs, including trees and vegetation, as well as green roofs, cool the urban surface via evapotranspiration [3]. Second, GBAM, including cool pavements and cool roofs, creates a cooling effect by suppressing overheating through the reflection of radiant energy from the sun using high-albedo materials coated onto surfaces [8; 9]. Third, the shadows formed by the leaves and stems of trees and vegetation and green roofs in UGSs generate a cooling effect by providing shielding from solar radiation [10; 11]. HICS effectiveness has been quantitatively analyzed indoors and outdoors by observing changes in meteorological factors such as temperature and humidity using meteorological sensors [12]. Laboratory observations/experiments are effective for measuring HICS effectiveness while excluding external influences [13; 14; 15]. However, there are difficulties in replicating an actual urban environment, such as the challenges involved in creating an artificial climate. In field experiments, HICS effectiveness was analyzed for specimens artificially created with HICS-related techniques in places where the external environment is limited, including rooftops [16; 17; 18; 19; 20; 21; 22]. This observation-based analysis method can verify the effect in the experimental field setting of HICS. However, actual urban environments exhibit distinct thermal environments according to the prevailing spatial and temporal conditions. Actual urban environments are composed of various structures, including buildings and roadside trees, which have diverse spatial densities (SDs). These diverse SDs in cities make important contributions to the formation of an urban thermal environment [23; 24; 25]. The sky view factor (SVF) is a key index used to determine the relationship between SDs and urban thermal environments [26]. The SVF, which quantitatively represents the fraction of sky visible from the ground surface, has a value between 0.0 and 1.0 [27]. Many studies have demonstrated a relationship between SVF and the urban thermal environment [28; 29]. [PERSON] et al. [29] reported that there are differences in heat environment aspects between cities with high and low SDs [29]. The land surface temperature (LST) distribution in urban thermal environments also differs according to temporal conditions. [PERSON] et al.