Subsurface heat island across the Chicago Loop district: Analysis of localized drivers

The subsurface beneath urban areas worldwide is warming up, leading to so-called subsurface urban heat islands. Despite many investigations, limited knowledge is available on the sources (e.g., localized drivers) of subsurface urban heat islands. This paper presents an unprecedented Internet of Things facility to unravel key features characterizing localized drivers of subsurface urban heath islands: a network composed of >150 wireless temperature sensors deployed in surface and subsurface environments across the Chicago Loop district. Through this facility, the study unravels a subsurface urban heat island in the Loop and indicates marked and highly heterogeneous temperatures for localized drivers of such underground climate change. The temperatures of localized drivers characterizing the monitored subsurface heat island can exceed by >25 °C the ground temperature, involving a continuous heat transfer towards this medium. The temperatures of such drivers can further differ by >15 °C across the studied district, not only when different drivers are examined, but also when different locations within the same driver are considered. The identified features of localized drivers of subsurface urban heat islands arguably characterize many cities worldwide, requiring adequate modeling approaches and uncertainty quantifications in future simulation studies on such pervasive phenomena.