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

The silent impact of underground climate change on civil infrastructure

“…Temperature sensing network. The temperature sensing network at the basis of this work, together with the Chicago Loop district where it is deployed, have been extensively characterized in other studies 22,56 . Therefore, their features are only described succinctly in this section.…”

“…Since 2019, temperature sensors have been deployed in a myriad of surface and subsurface environments in the Chicago Loop district, which is also known as “the cake” for its various levels of built environments above and below the ground surface. The aim of this endeavor has been threefold: (1) gather surface air temperature data for the downtown area of Chicago that can enrich complementary sensing endeavors for Chicagoland and Illinois 57 , 58 , (2) establish relationships between the surface air temperature and the air temperature in underground built environments in the downtown area of Chicago 22 , and (3) measure ground temperatures in the heart of Chicago 22 .…”

“…Motivated by the lack of a fundamental understanding of the impacts of subsurface heat islands on the performance of civil infrastructure, this study addresses such knowledge gap and validates its underlying hypothesis with reference to a real case study: the Chicago Loop district—the most densely populated district in the US after Manhattan, which suffers from an urban heat island 22 . Two facilities are used to explore this complex problem: a 3-D computer model of the Chicago Loop and a wireless temperature sensing network installed in surface and subsurface environments across such district.…”

“…The fundamental hypothesis behind this work is that subsurface heat islands represent a silent hazard for urban areas, with detrimental possibilities for the performance of civil infrastructure. This hypothesis relies on three considerations: (1) soils, rocks, and construction materials are affected by temperature variations, undergoing thermally induced deformations and property changes that can be reversible or irreversible over time 45 , 46 ; (2) the average temperature of the shallow subsurface in urban areas is rising at an alarming rate, with recorded ground temperature anomalies in the core of dense city districts that can achieve up to +20 °C 6 , 9 , 15 , 22 ; (3) comparable temperature variations to those that are currently measured in the subsurface of urban areas have shown to represent an issue for the geotechnical and structural performance of geothermal structures and infrastructures, and for this reason, must now be considered in their design 47 , 48 ; however, no existing civil structure or infrastructure in cities has been designed to account for rising ground temperatures and is hence prone to operational issues due to subsurface heat islands.…”

“…Proportional to urban density and population 6,19 , and dependent on topography and hydrogeology of the urban space 20 , subsurface urban heat islands are an alarming phenomenon for urban areas, which can often be more intense than their surface counterpart 21 . A recent review of the literature suggests that subsurface heat islands are causing in various cities across the world an increase in average ground temperature between 0.1 and 2.5 °C per decade down to 100 m of depth 22 . Studies highlight multiple impacts of subsurface temperature rises on urban areas.…”