Environmental Engineering and Management Journal March 2015, Vol.14, No. 3, 647-655 http://omicron.ch.tuiasi.ro/EEMJ/ “Gheorghe Asachi” Technical University of Iasi, Romania IMPACT OF URBANIZATION ON URBAN HEAT ISLAND EFFECT BASED ON TM IMAGERY IN WUHAN, CHINA Qijiao Xie1, Zhixiang Zhou2 1School of Resources and Environmental Science, Hubei University, 430062 Wuhan, China 2College of Horticultural & Forestry Science/Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, 430070 Wuhan, China Abstract As natural landscapes are increasingly replaced by impervious surface materials associated with urbanization, urban areas tend to experience higher surface temperatures when compared to rural areas, which is known as the urban heat island (UHI) effect. In this study the impact of urbanization on land surface temperature (LST) and the UHI effect were examined based on two Landsat Thematic Mapper (TM) imageries of 1987 and 2007. Results show that Wuhan experienced rapid urban expansion from 1987 to 2007, while the areal extent with higher temperatures did not always correspond to the urbanized area. The percent impervious surface area (ISA) was found to efficiently explain the LST variation in urban areas, especially in high-density ones. The normalized difference vegetation index (NDVI) was a sufficient indicator to express surface temperature variation only in natural context. These findings help urban planners and greening designers make appropriate decisions on urban planning and thermal management. Key words: impervious surface area, land surface temperature, normalized difference vegetation index, remote sensing, urban thermal environment Received: March, 2012; Revised final: April, 2013; Accepted: May, 2013 1. Introduction powerful force in local climate change (Du et al., 2007; Luber and McGeehin, 2008; Zheng et al., One of the environmental consequences of 2014). With the rapid increase of population and urbanization and industrialization is the urban heat buildings in urban areas, anthropogenic waste heat island (UHI) effect, a phenomenon of higher released from vehicles, air conditioners, power plants atmospheric and surface temperatures occurring in and industries have steadily increased (Manea et al., urban areas than in surrounding rural areas (Gluch et 2013), which heats up the urban environment al., 2006; Voogt and Oke, 2003). Higher urban directly. Urban development can tremendously alter temperatures generally result in adverse economic the urban surface structures by replacing natural and environmental impacts locally, regionally and landscapes with a large expanse of non-evaporating globally. Persistent higher temperatures increase the impervious surfaces such as concrete and asphalt demand for air conditioning, raise pollution levels, (Oke, 1982; Owen et al., 1998; Tang et al., 2014). change urban thermal environments and ultimately Physical change of the urban surface (albedo, thermal lead to thermal discomforts and incidence of heat- capacity, heat conductivity) can affect urban surface related illnesses. temperatures by altering the sensible and latent heat The UHI effect is essentially a thermal exchange between the urban surface and boundary pollution caused by human activity and regarded as a layers (Frey and Parlow, 2012; Mohan and Kandya, Author to whom all correspondence should be addressed: e-mail: [email protected]; Phone: +86-27-87284232; Fax: +86-27- 87282010 Xie and Zhou/Environmental Engineering and Management Journal 14 (2015), 3, 647-655 2015). The land surface temperature (LST) will between LST, NDVI and percent ISA in past unavoidably propagate both downward into the literatures. However, further investigation on the subsurface (Baker and Baker, 2002; Taniguchi et al., correlation between LST and NDVI at different 2005) and upward into atmosphere (Brazel et al., levels of urban development is necessary. This study 2007; Jin et al., 2011; Jones et al., 1990). Then aims to examine the urban expansion and its impact surface, subsurface and air urban heat islands can be on urban surface temperatures and the surface UHI detected (Roth et al., 1989; Voogt and Oke, 2003). effect and also to analyze the varied efficiency of Urbanization typically leads to the reduction vegetation on reducing surface temperatures in of green spaces in urban areas, which modifies urban different urban developed areas. The ultimate goal is surface water content and vegetation cover (Owen et to provide a better understanding of the relationship al., 1998). Research found that, with regard to the between LST, NDVI and percent ISA, and allow surface energy balance, latent heat exchange was urban planners and managers to control and manage dominant in more vegetated areas, while sensible the urbanization and associated thermal pollution. heat exchange was dominant in impervious areas (Oke, 1982). This finding is attracting mounting 2. Case studies attention on the relationship between LST and urban vegetation. Much emphasis has been placed on the 2.1. Study area description relationship between LST and the normalized difference vegetation index (NDVI) (Gallo et al., The study area is Wuhan city, located at 1993; Lo et al., 1997; Nonomura et al., 2009; Owen 113°41’~115°05’E, 29°58’~31°22’N. Wuhan is the et al., 1998; Price, 1990; Raynolds et al., 2008) or capital of Hubei province, situated at the center of other NDVI-related parameters, such as vegetation central China and in eastern Hubei, where the abundance (Gillies and Carlson, 1995; Lo et al., Yangtze River joins the Han River. It covers an area 1997; Weng, 2001) and vegetation fraction (Gutman of over 8000 km2, with a population of more than 8 and Ignatov, 1998; Weng et al., 2004). Results million. It has a long history of more than 3500 indicate that there is a negative correlation between years. It is an economic center and an important LST and NDVI, which is valuable for UHI and urban transportation pivot of China. The metropolitan area climate studies. comprises three parts: Wuchang, Hankou and On the other hand, much attention was paid on Hanyang, commonly called Three Towns of Wuhan. land cover changes associated with urbanization and These three parts face each other across the rivers their impact on LST (Fabrizi et al., 2010; Hamdi, and are linked by bridges. 2010; Liu and Zhang, 2011; Xiong et al., 2012). The Wuhan is situated in the north-subtropical rapid changes of land use and land cover in urban climatic zone with four distinctive seasons. Spring areas result in the increase of impervious surface and autumn are generally mild, while winter is cool areas (ISA) in urban area. Because the amount of with occasional snow. Due to its oppressively hot and ISA is closely related to population growth and urban humid summers, Wuhan is commonly known as one expansion, it was used to quantify the degree of of the Three Furnaces of China, along with Nanjing urbanization and extent of urban land use (Carlson, and Chongqing. The annual temperature is 15.8°Cto 2012; Civco et al., 2002; Essa et al., 2013; Lynn et 17.5°C with extreme temperatures ranging from al., 2009; Xian and Crane, 2006; Yang et al., 2003; −18.1°Cto 42.0°C. The annual average precipitation Yuan and Bauer, 2007) and indicate the is 1269 mm, concentrated during June to August. The environmental quality (Arnold and Gibbons, 1996; annual frost free period lasts 211 to 272 days and Xiao et al., 2007). Increased concern has been annual sunlight duration is 1810 to 2100 hours. directed to the comparative studies of NDVI and percent ISA as indicators of surface urban heat island 2.2. Derivation of LST, NDVI and related indexes effect based on Landsat imagery by investigating the from Landsat TM imageries relationships between the LST, percent ISA and the NDVI (Deng and Wu, 2013; Ma et al., 2010; Yuan LST data were derived from the thermal and Bauer, 2007; Zhang et al., 2009). Compared to infrared (TIR) band (band6) of the radiometrically the NDVI, the percent ISA was found to be more and geometrically corrected images (Voogt and Oke, stable and less affected by seasonal changes in 2003), which was conducted in Erdas Imagine 9.2 urbanized environment. Therefore, it is important to with several procedures: radiometric calibration, at- analyze the relationship between the LST and percent satellite temperature calculation, emissivity ISA in urban areas, for it provides an effective correction and LST estimation. In this study, we used method to study urban expansion and related UHI two Landsat-5 Thematic Mapper (TM) images effect. acquired on September 26, 1987 and April 10, 2007. LST is useful to predict the energy and water At first, the DN value of Landsat TM band6 was exchanges between land surface and atmosphere, converted into spectral radiance (Chander and which plays an important role in human–environment Markham, 2003). The spectral radiance was then interactions. Urban expansion and development and converted into at-satellite temperature (i.e., their adverse effect on urban thermal environment blackbody temperature or brightness temperature) has been confirmed by analyzing the relationship under the assumption of uniform emissivity. The at- 648 Impact of urbanization on urban heat island effect based on TM imagery in Wuhan, China satellite temperature obtained was referenced to a 3. Results black body and not the real surface temperature. Therefore, emissivity corrections became necessary 3.1. Spatial pattern of the percent ISA according