Abstract
The Urban Heat Island (UHI) is one of the most well documented phenomena in urban climatology. Although a range of measurements and modelling techniques can be used to assess the UHI, the paucity of traditional meteorological observations in urban areas has been an ongoing limitation for studies. The availability of remote sensing data has therefore helped fill a scientific need by providing high resolution temperature data of our cities. However, satellite-mounted sensors measure land surface temperatures (LST) and not canopy air temperatures with the latter being the key parameter in UHI investigations. Fortunately, such data is becoming increasingly available via urban meteorological networks, which now provide an opportunity to quantify and compare surface and canopy UHI on an unprecedented scale. For the first time, this study uses high resolution air temperature data from the Birmingham Urban Climate Laboratory urban meteorological network and MODIS LST to quantify and identify the spatial pattern of the daytime and night-time UHI in Birmingham, UK (a city with an approximate population of 1 million). This analysis is performed under a range of atmospheric stability classes and investigates the relationship between surface and canopy UHI in the city. A significant finding of this work is that it demonstrates, using observations, that the distribution of the surface UHI appears to be clearly linked to landuse, whereas for canopy UHI, advective processes appear to play an increasingly important role. Strong relationships were found between air temperatures and LST during both the day and night at a neighbourhood scale, but even with the use of higher resolution urban meteorological datasets, relationships at the city scale are still limited.
Highlights
IntroductionThe Urban Heat Island (UHI) continues to be a widely researched phenomenon concerning the difference in temperature between an urban area and the rural surroundings of a conurbation
The image availability tends to increase with atmospheric stability for the night pass, whereas for daytime conditions the majority of imagery was available for the moderately unstable classes
The Urban Heat Island (UHI) is clearly present in both datasets, both day and night, and over a range of atmospheric stability classes
Summary
The Urban Heat Island (UHI) continues to be a widely researched phenomenon concerning the difference in temperature between an urban area and the rural surroundings of a conurbation. A range of factors contribute to the occurrence of the UHI; increased emissions of anthropogenic heat flux, changes to urban geometry and the replacement of vegetation cover by construction material (e.g., asphalt and concrete)—all of which directly change surface albedo, emissivity and Remote Sens. It was found that urban temperatures tend to be slightly warmer than rural ones during the daytime in London with morning urban and rural temperatures being similar, but scenarios exist where urban temperatures can be cooler than surrounding rural areas [3]. Systematic reviews of the UHI literature are available in [4,5] and both document a range of studies that have investigated both nocturnal and daytime temperature differences
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