Abstract
Differences between the energy balance of cities and their non-urban surroundings exist due to modification of surface properties. In temperate and sub-tropical climates, these differences are manifest as the Urban Heat Island (UHI) effect. However in more arid environments man-made modifications of the environment can cause urban cooling relative to the surrounding landscape particularly during the dry season. This research examines the spatial formation of the daytime Surface Urban Cool Island (SUCI) effect of Erbil city in Iraq, as a case study of cities in semi-arid climates. Six satellite images acquired by Landsat 8 during the period from 1st July to 19th September 2013 are used to retrieve Land Surface Temperature (LST), identify Land Use/Land Cover (LULC) classes and investigate the spatial variation of LST and the SUCI intensity. In order to find out the key drivers of the observed patterns of LST, the relationship with wetness, brightness, bareness, built-up and vegetation index maps are examined. The results indicate that densely built-up areas, such as central districts of the city, green areas and water bodies, had lower LST acting as cool islands, compared to the non-urbanized area around the city. In contrast, the airport, open spaces and new low-density housing developments on the outskirts of the city, experienced higher LST and showed an SUHI effect. A very strong inverse relationship is evident between surface temperature and wetness index (r=−0.9; p<0.01). A strong positive correlation (r=0.75; p<0.00001) is apparent with the brightness index. In contrast, between surface temperature and the greenness index a moderate negative correlation was found (r=−0.39; p<0.01) for a typical dry season day. The results show that during the daytime residential areas in the city centre recorded an LST of 46.2±1.74°C. Urban Cool Island Intensity (UCII) of the city ranged from 3.5 to 4.6°C compared to a 10km buffer zone around the city. This study shows that during the dry season in some cities, such as Erbil, the surface wetness is the main determinant of the UCI effect, and not vegetation cover.
Highlights
This urban extension causes temperatures to increase in temperate and sub-tropical climates, a phenomenon known as the Urban Heat Island (UHI) effect (Ore, 1987; Weng et al, 2004; Farina, 2011)
The results of this study indicate a daytime Surface Urban Cool Island (SUCI) effect and they differ in this finding from other published studied of the UHI in densely vegetated regions (e.g. (Tran et al, 2006; Shahmohamadi et al, 2012; Dhorde and Dhorde, 2012)
Inside the city centre and high-density districts, the surface temperature is reduced in comparison to the surroundings of the city
Summary
Urban expansion can lead to radical changes in the nature of the surface of the urbanized area. This urban extension causes temperatures to increase in temperate and sub-tropical climates, a phenomenon known as the Urban Heat Island (UHI) effect (Ore, 1987; Weng et al, 2004; Farina, 2011). Built-up areas in semi-arid regions have been found to exhibit lower surface temperatures compared to non-urbanized dry surroundings (Frey et al.; Cai and Du, 2009; Shigeta et al, 2009), which has been termed the Urban Cool Island (UCI) effect
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
