## 2 Materials and Methods
### Selection of Assessment Indices and Methods  
A regulating service is defined as the benefit of the regulatory function provided by the material cycle processes of an ecosystem [2; 3; 4]. In other words, it is possible to analyze a regulating service by calculating the enhancement in positive effects or reduction in negative environmental load so that the urban ecosystem can cycle virtually. Additionally, the South Korean Ministry of Environment has recently focused on national research projects to improve vegetation vitality, flood reduction capacity, carbon storage capacity, and heat reduction capacity among ERS [41]. Moreover, policy efforts are being made to restore and promote the health of urban ecosystem by improving ERS through institutional means, such as urban environmental planning and environmental impact assessment. Therefore, this study selected vegetation vitality, flood reduction capacity, carbon storage capacity, and heat reduction capacity as the main assessment indices of urban ecosystem and based the assessment on the physical characteristic of the ERS. Vegetation vitality refers to the distribution amount and vigor of vegetation, and the higher the vegetation vitality, the more active the growing state [21; 42; 43; 44]. In addition, with higher vegetation vitality, better habitats can be created [21]. The regulating service increases the foundation for the virtuous cycle of the ecosystem [45; 46]. In particular, numerous studies have shown that the higher the vegetation capacity, the greater the regulatory services, such as flood reduction capacity, carbon storage capacity, and heat reduction capacity [47; 48]. Vegetation vitality can be assessed with a normalized difference vegetation index (NDVI) analysis, developed by [PERSON] et al. (1974) [42], using satellite  
Figure 1: Study procedure. images. In this study, the vegetation vitality of the study area was calculated by acquiring Landsat satellite images from days with low cloudiness and excellent vegetation vitality and analyzing the NDVI. Furthermore, vegetation areas in the city contribute to flood prevention by storing rainwater, which delays the peak time and reduces the peak amount [22; 23; 49; 50; 51; 52]. This effect can be estimated using the curve number (CN) value developed by the US Bureau of Land Management. CN is a coefficient used to estimate effective rainfall by analyzing detailed data on soil characteristics, cover condition, and preceding precipitation conditions [52; 53]. CN is very useful in studies that calculate the flood reduction capacity of urban ecosystem that include green infrastructure. In this study, the South Korean runoff curve index according to land cover suggested by the South Korean Ministry of Environment was calculated considering the area occupied by each grid. The CN has a value between 0 and 100, and the closer the value is to 100, the higher the impermeability. For easy comparison with other regulating service assessment results, this study assessed the result of subtracting the CN value from 100 as the flood control ability. Urbanization is accelerating climate change by causing increases in human activity and traffic, which emit greenhouse gases. Urban forests, parks, green spaces, and street trees absorb and store greenhouse gases in the atmosphere through photosynthesis [5; 6; 54; 55]. This carbon storage capacity is calculated by dividing it into soil carbon storage and vegetation carbon storage. Soil carbon storage can be calculated using the carbon storage unit of each soil type, and vegetation carbon storage can be calculated using the biomass allometric equations according to IPCC guidelines (2006) [56]. Cities have the structural characteristic of discharging much heat because of land cover and buildings, and this discharge causes the urban heat island phenomenon [57; 58; 59; 60]. Green infrastructure such as urban forests and street trees are attracting attention as important planning elements that can reduce such heat generation through transpiration [5; 54; 61; 62; 63].