The Effect of Horizontal Advection on the Nocturnal Surface Urban Heat Island Using MODIS Satellite over Birmingham and the West Midlands, United Kingdom

It has been well-recognised that the horizontal advection can modulate the downwind footprint of the urban heat island (UHI). However, limited studies have considered the urban heat advection (UHA) generated from this boundary-layer process, mainly due to the lack of a dense network of sensor to sufficiently resolve the local climate in a city. For the first time, this study explores the possible influence of the horizontal advection on the nocturnal surface urban heat island sensed by the MODIS satellite (sUHA) over a ten-year period. Results show that the heat transport from urban to downwind areas can be observed by the satellite instrument. A significant warming up to 0.5 ºC and 1.7 ºC were found at city (Birmingham) and regional scale (West Midlands area), respectively. The amplification of the sUHA at regional scale was largely attributed to the topography effects according to the significant correlation between sUHA and a topography index (i.e. R²=0.53). An approximate 0.5 ºC can be corrected for sUHA after minimising the topography impact by applying a statistical method. Overall, this study highlighted the value of the satellite instrument to investigate the UHA at both city and regional scale. However, more importantly, the topography was found to have considerable influences on regulating the heat transfer from urban to its downwind areas, which provides further implications for urban planning and risk management with respect to the UHI.