The world's urban infrastructure faces a growing peril, and the ancient buildings that define many European cities are particularly vulnerable. A recent study has unveiled the hidden danger of subsurface climate change, which poses a significant threat to modern cities, while simultaneously revealing how ancient structures are especially at risk in the face of these modern challenges.
In urban areas globally, a silent hazard known as subsurface climate change or subsurface heat islands has been steadily heating the ground beneath our feet. This phenomenon, driven by human activity and solar radiation, is causing the ground to warm at an alarming rate, with temperatures increasing by 0.1 to 2.5 degrees Celsius per decade beneath cities.
Recent research conducted by Northwestern University has highlighted the extent of this issue. In their study led by Professor Alessandro Rotta Loria, the team installed a network of over 150 temperature sensors throughout the Chicago Loop, including beneath buildings, in subway tunnels, underground parking garages, and streets. Data from this network showed that underground temperatures beneath the Loop can be up to 10 degrees warmer than in areas like Grant Park, away from urban structures.
What makes this phenomenon particularly concerning is its impact on civil infrastructure. As the ground heats up, it deforms, causing building foundations and the surrounding ground to move excessively. This movement, driven by expansions and contractions, can result in cracks and structural damage, ultimately affecting the long-term operational performance and durability of buildings.
The study serves as a wake-up call to urban areas worldwide, emphasizing the need for a comprehensive strategy to address subsurface climate change and protect both modern and historic structures. The delicate balance between preserving the past and preparing for the future is now more crucial than ever as cities grapple with this dual threat.
Professor Rotta Loria explains, "It's not like a building will suddenly collapse. Things are sinking very slowly. The consequences for serviceability of structures and infrastructures can be very bad, but it takes a long time to see them."
However, the vulnerability of historic buildings, especially prevalent in European cities with their ancient architecture, adds an additional layer of complexity to this issue. Many of these buildings were constructed before the emergence of subsurface climate change as a significant concern.
"European cities with very old buildings will be more susceptible to subsurface climate change," warns Rotta Loria. "Buildings made of stone and bricks that resort to past design and construction practices are generally in a very delicate equilibrium with the perturbations associated with the current operations of cities."
The thermal perturbations linked to subsurface heat islands can have detrimental impacts on such structures, potentially leading to increased wear and damage over time.
In light of these findings, urban planners and architects are now faced with the challenge of adapting existing infrastructure and designing new buildings that can withstand these temperature variations. Solutions may include incorporating geothermal technologies to harvest waste heat for space heating and installing thermal insulation to minimize heat transfer to the ground.