Abstract
For the first time, an extensive study of the surface urban heat island (SUHI) in Thailand’s six major cities is reported, using 728 MODIS (MODerate Resolution Imaging Spectroradiometer) images for each city. The SUHI analysis was performed at three timescales—diurnal, seasonal, and multiyear. The diurnal variation is represented by the four MODIS passages (10:00, 14:00, 22:00, and 02:00 local time) and the seasonal variation by summer and winter maps, with images covering a 14-year interval (2003–2016). Also, 126 Landsat scenes were processed to classify and map land cover changes for each city. To analyze and compare the SUHI patterns, a least-square Gaussian fitting method has been applied and the corresponding empirical metrics quantified. Such an approach represents, when applicable, an efficient quantitative tool to perform comparisons that a visual inspection of a great number of maps would not allow. Results point out that SUHI does not show significant seasonality differences, while SUHI in the daytime is a more evident phenomenon with respect to nighttime, mainly due to solar forcing and intense human activities and traffic. Across the 14 years, the biggest city, Bangkok, shows the highest SUHI maximum intensities during daytime, with values ranging between 4 °C and 6 °C; during nighttime, the intensities are rather similar for all the six cities, between 1 °C and 2 °C. However, these maximum intensities are not correlated with the urban growth over the years. For each city, the SUHI spatial extension represented by the Gaussian footprint is generally not affected by the urban area sprawl across the years, except for Bangkok and Chiang Mai, whose daytime SUHI footprints show a slight increase over the years. Orientation angle and central location of the fitted surface also provide information on the SUHI layout in relation to the land use of the urban texture.
Highlights
Urban heating is usually quantified by means of the urban heat island (UHI), a well-known anthropogenic thermal modification whose effects have implications for human comfort and health, ecosystem function, local weather, air pollution, urban planning, and energy management [1,2,3,4]
Six major cities in Thailand were selected for this study (Figure 1), including: (1) Bangkok (BG), the capital of Thailand, located in the central region; (2) Chiang Mai (CM), the largest city in the northern region, and four large cities located in northeastern region: (3) Nakhon Ratchasima (NR); (4) Ubon Ratchathani (UR); (5) Khon Kaen (KK); and (6) Udon Thani (UT)
These surface urban heat island (SUHI) patterns were examined during a 14-year interval (2003–2016): for example, the SUHI during 2013 for the six cities is shown in Figure 4 considering the summer season at 22:00
Summary
Urban heating is usually quantified by means of the urban heat island (UHI), a well-known anthropogenic thermal modification whose effects have implications for human comfort and health, ecosystem function, local weather, air pollution, urban planning, and energy management [1,2,3,4]. SUHI map images were extensively retrieved by using Landsat data, providing spatiotemporal analysis and allowing the modeling of the urban thermal patterns with the land cover classes [13,14,15]. A SUHI insight over the land use zoning plan of Bangkok using seven Landsat 8 scenes was proposed [28] To bridge this gap, this work provides, for the first time, an extensive temporal and spatial investigation in Thailand by examining the SUHI of six major cities located in different geographic regions during a long-time interval (2003–2016) using 728 MODIS images, allowing daytime and nighttime monitoring. The study was carried out by means of a two-dimensional least-square Gaussian fitting technique, whose parameterization and visualization proves to be useful in SUHI pattern insight
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