Analysis of Urban Heat Island Intensity Among Administrative Districts Using GIS and MODIS Imagery*
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Journal of the Korean Association of Geographic Information Studies, 20(2) 2017, pp. 1-16 ISSN 1226-9719(Print)On https://doi.org/10.11108/kagis.2017.20.2.001 ISSN 2287-6952(Online) Analysis of Urban Heat Island Intensity Among Administrative Districts Using GIS and MODIS Imagery* Kyeong-Ho SEO1· Kyung-Hun PARK2※ GIS 및 MODIS 영상을 활용한 행정구역별 도시열섬강도 분석* 서경호1·박경훈2※ ※ ABSTRACT This study was conducted to analyze the urban heat island(UHI) intensity of South Korea by using Moderate Resolution Imaging Spectroradiometer(MODIS) satellite imagery. For this purpose, the metropolitan area was spatially divided according to land cover classification into urban and non-urban land. From the analysis of land surface temperature(LST) in South Korea in the summer of 2009 which was calculated from MODIS satellite imagery it was determined that the highest temperature recorded nationwide was 36.0℃, lowest 16.2℃, and that the mean was 24.3℃, with a standard deviation of 2.4℃. In order to analyze UHI by cities and counties, UHI intensity was defined as the difference in average temperature between urban and non-urban land, and was calculated through RST1 and RST2. The RST1 calculation showed scattered distribution in areas of high UHI intensity, whereas the RST2 calculation showed that areas of high UHI intensity were concentrated around major cities. In order to find an effective method for analyzing UHI by cities and counties, analysis was conducted of the correlation between the urbanization ratio, number of tropical heat nights, and number of heat-wave days. Although UHI intensity derived through RST1 showed barely any correlation, that derived through RST2 showed significant correlation. The RST2 method is deemed as a more suitable analytical method for measuring the UHI of urban land in cities and counties across the country. In cities and counties with an urbanization ratio of < 20%, the rate of increase for UHI intensity in proportion to increases in urbanization ratio, was very high; whereas this rate gradually declined when the urbanization ratio was > 20%. With an increase of 1℃ in RST2 UHI intensity, the number of tropical heat nights and heat wave days was predicted to increase by approximately five and 0.5, respectively. 2016년 6월 8일 접수 Received on June 8, 2016 / 2017년 1월 31일 수정 Revised on January 31, 2017 / 2017년 2월 7일 심사완료 Accepted on February 7, 2017 * This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT & Future Planning(NRF-2016R1A2B4015460). 1 창원대학교 친환경해양플랜트FEED공학과정 Department of Eco-friendly Offshore Plant FEED Engineering, Changwon National University 2 창원대학교 환경공학과 Department of Environmental Engineering, Changwon National University ※ Corresponding Author E-mail : [email protected] 2 Analysis of Urban Heat Island Intensity Among Administrative Districts Using GIS and MODIS Imagery These results can be used for reference when predicting the effects of increased urbanization on UHI intensity. KEYWORDS : MODIS Satellite Imagery, Urban Heat Island, Land Surface Temperature, Tropical Night, Urbanization Ratio 요 약 본 연구는 MODIS 위성영상을 활용하여 우리나라 전역의 열섬강도를 분석하기 위하여 연구를 수행하였다. 이를 위해 도시지역을 토지피복별 분류에 따라 시가화지역, 비시가화지역으로 공간적 구분하였다. MODIS 위성영상을 활용하여 산출된 2009년 여름철 전국의 표면온도 분석 결과 전 국 최고온도는 36.0℃, 최저온도 16.2℃, 평균 24.3℃, 표준편차 2.4℃로 분석되었다. 시군별 열 섬현상을 분석하기 위하여 시가화지역과 비시가화지역의 평균온도의 차이를 열섬강도로 정의하였 고 RST1, RST2 2가지 방법으로 산출하였다. 그 결과 RST1의 경우 열섬강도가 높은 지역이 산 포되어 분포하고 있는 것으로 나타났으며, RST2의 경우 대도시지역을 주변으로 열섬강도가 높은 지역이 집중되어 있는 것으로 분석되었다. 시군별 열섬현상 분석에 효율적 방법을 보기 위하여 시 가화율, 열대야일수, 폭염일수와의 상관분석을 하였다. 그 결과 RST1 방식에 의한 열섬강도는 상 관성이 거의 없는 것으로 나타났으며, RST2의 경우 유의한 상관성을 나타났다. 전국 시군별 도시 지역을 대상으로 열섬현상에 대해 분석하기 위한 방법으로는 RST2 방식이 더 적합할 것으로 판 단되며, 시군별 시가화율이 약 20% 이하일 경우 시가화율 증가에 따른 도시지역의 열섬강도의 증 가율이 매우 높았으며, 약 20% 이상부터 열섬강도의 증가율이 점차 낮아지는 것을 확인할 수 있 다. RST2 열섬강도가 1℃ 증가할 경우 열대야일수와 폭염일수는 약 5일과 0.5일 증가하는 것으 로 예측하였다. 이러한 분석결과는 추후 도시화율 증가에 따른 열섬강도 변화를 예측 할 수 있는 자료로서 활용될 수 있을 것으로 판단된다. 주요어 : MODIS 위성영상, 도시열섬현상, 지표면온도, 열대야, 시가화율 a temperature difference of more than 2℃ INTRODUCTION between urban and non-urban land (Oke, 1987; Ministry of Agriculture and Forestry, Rapid industrialization in modern society 2007; Takebayashi and Moriyama, 2009; has led to the acceleration of indiscreet Song and Park, 2012). UHI has a negative development and expansion, which has in influence on the pleasant living environ- turn resulted in a gradual increase in ment and high life satisfaction of city urban land. Overpopulation, increases in residents, because it worsens the heat man-made structures, and changes in problems on tropical nights and the heat terrain brought forth by urbanization along waves in summer(Kovats and Hajat, 2008; with deterioration of the urban environment Song and Park, 2013; Song, 2014). Accor- have been reported, as the primary causes dingly, recognizing the current state and of urban heat island(UHI) an effect in problems of, and preparing countermeasures which the change in urban climate leads to against, UHI can be regarded as pressing GIS 및 MODIS 영상을 활용한 행정구역별 도시열섬강도 분석 / 서경호· 박경훈 3 issues that need to be considered in order physical environmental factors existing in to alleviate these problems in urban cities if a mitigation strategy is to be environments, particularly in relation to planned for reduction of UHI(Kim and climate change(Ymashita, 1995). Yeom, 2012); therefore, current studies on In addition to urbanization, the focus on the causes of and solutions to UHI widely development around metropolitan areas can underway. Previous research on these be regarded as an important factor that issues has focused on the need for exacerbates UHI. Concentration of the changing urban land cover materials and urban population further increases the urban afforestation as solutions to UHI. demand for developing residential and This is reasonable, given that UHI is commercial buildings; thus, traffic facilities, induced by increases in the numbers of and cities have become covered with roads and buildings in urban areas, which artificial land cover rather than forests. in turn cause tropical heat nights, increased Among such surface materials, asphalt and environmental pollution, and severe health concrete in particular, can negatively affect problems for urban residents(Kim et al., 2001). the urban climate by increasing the heat Furthermore, because the temperature data on tropical nights, because they absorb and obtained from imagery are arranged in a retain heat during the day and release it at space lattice form, they enable direct night (Park, 2001; Lee et al., 2007; Song comparison with physical environmental and Park, 2015). factors in cities such as land cover(Song, Another factor that causes UHI is the 2014). This has led to studies for deter- prioritization of function, efficiency, and mining methods of lowering UHI by const- convenience above climate and environment ructing a GIS-integrated database that in the existing processes of urban develo- incorporates remote sensing and the pment. Notably, greater emphasis has been factors causing UHI, the results of which placed on improving indoor comfort as are used to map the decrease in fores- opposed to the outdoor environment of a tation and changes in urban land usage city, which has resulted in the installation (Ministry of Agriculture and Forestry, 2007). of air conditioning systems in most buil- To this end, Song(2014) determined the Land dings in order to maintain indoor temper- surface temperature(LST) of Changwon City atures. However, recent climate change has by using satellite imagery, and analyzed increased heat stress and the occurrence the effect of various LST due to urban of abnormal weather(e.g., heat waves and land usage, on the UHI effect. Ahn(2007) cold waves) has led to excessive use of investigated changes from past land use interior cooling and heating systems. This and evaluated the effect of various land has resulted in the exacerbation of UHI uses on the thermal environment, the because artificial heat in cities has sharply results formed basis for eco-friendly increased, particularly in summer(Suh et urban planning. al., 2009; Park et al., 2011). Although several previous studies have It is important to understand the UHI been conducted on UHI by using satellite characteristics in addition to various imagery, those that engage in comparative 4 Analysis of Urban Heat Island Intensity Among Administrative Districts Using GIS and MODIS Imagery research between regions or discuss METHODS climate change on a large scale are insufficient because most existing studies 1. Research Process have approached the topic from a regional The process of this research is shown perspective. The purpose of this study is in Figure 1. Initially, 2009 spatial and to analyze the causes and effects of UHI climate information including MODIS imagery in South Korea at the national level by data, land cover maps, and the numbers of using applicable Moderate Resolution Imaging tropical heat nights and heat wave days Spectroradiometer (MODIS) satellite imagery. was collected. For the land cover map, the For this purpose, a method for evaluating 2009 level 2 classification of land cover of UHI intensity through regional comparison the Ministry of Environment was adopted is proposed. Moreover, this study was to categorize urban and non-urban land, conducted to identify the current state and from which the urbanization ratio was causes of UHI in a practical sense by calculated. For the MODIS data, coordinate examining the relationship between contr- calibration and unitary transformation were oversial topics such as the expansion of applied to determine LST, and UHI intensity urban lands and UHI intensity and by was calculated from the difference in LST analyzing the correlation between factors between urban and non-urban land.