Simulation of urbanization impacts on near surface temperature and urban heat island intensity under heat wave in Seoul, South Korea

Urban areas have different surface characteristics such as roughness length, airflow in urban canopies, and evapotranspiration from their rural surrounds due to human factors like high population density, traffic, and high-rise buildings. The characteristics increase the sensible heat flux and reduce latent heat flux in the surface energy balance of urban areas. Therefore, Urban canopy model has been developed and applied to reflect the characteristics of urban areas in mesoscale models. In this study, we investigate the impacts of urbanization on near surface temperature and urban heat island intensity in Seoul Metropolitan using the UM (Unified Model) with a MORUSES (Met Office Reading Urban Surface Exchange Scheme). The focus of our study is heat wave in the Seoul Metropolitan area that occurred from 1 to 5 August 2017. The study area is 126.6－127.6°E 37.1－37.8°N including Seoul Metropolitan. Simulations are performed with 2000s (2009-2010) land-use data and with 1980s (1989-1990) land-use data to investigate the urbanization impact during 20 years by land-use changing. The land-use data used the Korea Ministry of Environment level 1 class. Urban heat island intensities have been estimated based on the 1.5-m temperature difference between each simulation and the simulation of all urban land-use with replaced grass land-use. As a result, the urban fractions in the study area (Seoul Metropolitan) are 11% in the 1980s case and 18.2% in the 2000s case. Urban sprawl increased the daily 1.5-m temperature in urbanized area up to 2.5℃. Urban heat island intensity is significantly enhanced with urban sprawl and the daily mean Urban heat island intensity increased.