Beneath the Heatwave: The Rising Risks Climate Change Poses to Urban Subsurfaces

Rising global temperatures and urban heat accumulation are silently transforming underground environments, destabilizing soils, warming aquifers, and straining critical utilities and transit systems. The study warns that without coordinated planning and monitoring, subsurface warming could become a major hidden threat to urban resilience worldwide.

Rising global temperatures are forcing cities to confront not only the heat on their streets but a quieter, far more insidious crisis beneath them, one documented by researchers from Monash University Malaysia’s School of Engineering and its Climate-Resilient Infrastructure Research Hub. Their state-of-the-art review shows how the urban subsurface, tunnels, aquifers, pipes, cables, and energy systems are being reshaped by climate change and the intensifying Subsurface Urban Heat Island (SubSUHI) effect. As global temperatures climb roughly 1.45 °C above pre-industrial levels, urban environments trap more heat, pushing underground conditions into unfamiliar territory. This trapped heat, much of it generated by the infrastructure itself, is altering soil behavior, groundwater quality, and utility performance at a scale engineers are only beginning to understand.

How Warming Soil Undermines the Foundations of Cities

The review describes profound changes in soil thermal and moisture regimes, conditions essential for underground infrastructure stability. Most utilities sit shallow, within the top five meters, where soils are most vulnerable to drying and thermal stress. Moisture-sensitive clays shrink and swell more aggressively in hotter conditions, causing cracking, upheaval, and ground movement that can distort tunnels, fracture pipes, and undermine foundations. As rainfall patterns shift and flash droughts become more common, soil dries faster and deeper, compounding the structural risks. Many engineering codes still assume stable subsurface temperatures, a premise that no longer reflects reality.

Groundwater Heats Up, Triggering Chemical and Ecological Shifts

Urban aquifers are also warming, with temperature differences between rural and urban groundwater often reaching 2–7 °C. Car parks, basements, rail tunnels, and geothermal systems all radiate heat downward, gradually raising groundwater temperatures. This warming triggers chemical reactions that mobilize arsenic, nutrients, and toxic metals while disrupting microbial ecosystems. In cities relying heavily on groundwater for drinking and cooling, long-term thermal pollution could threaten supply reliability. The review warns that without coordinated thermal governance, urban aquifers may be pushed beyond their safe ecological and chemical limits.

Utilities Under Pressure: Water, Sewage, Power, and Fiber at Risk

Critical utility networks face intensifying stress as underground temperatures rise. Power cables buried in hotter soil lose current-carrying capacity and face overheating risks. Fiber-optic cables experience thermal distortion, affecting signal reliability. Drinking water pipes heat up, accelerating chlorine decay and enabling bacterial regrowth, while also raising levels of harmful trihalomethanes. Within households, stagnant tap water becomes more prone to microbial contamination. Sewage systems fare no better: warmer wastewater generates more hydrogen sulfide gas, speeding corrosion and worsening odors. Heat also concentrates pollutants, pharmaceuticals, heavy metals, and pathogens, creating increasingly complex challenges for aging wastewater treatment plants. These cascading effects highlight how warming temperatures threaten the reliability and safety of essential services.

Subways and Tunnels: Rising Heat Puts Transit Systems to the Test

Even in non-geothermal cities, subway tunnels routinely run 8–12 °C hotter than ambient air due to braking, ventilation, and passenger loads. In geothermal zones, surrounding rock can reach 70–100 °C, imposing severe thermal stresses on tunnel linings and accelerating concrete degradation. As outdoor temperatures rise, cooling demands for underground transit will surge. Existing ventilation systems, designed decades ago, may be quickly overwhelmed. Heat-related equipment failures, slower train speeds, and service disruptions are projected to become more common, directly affecting commuter reliability and operational costs. The review highlights innovative strategies such as waste-heat recovery, energy-efficient train designs, and geothermal-integrated tunnel cooling, though implementation remains uneven across cities.

A Call for Integrated Planning Beneath Urban Landscapes

Throughout the review, the authors emphasize that underground systems do not operate independently, soil affects groundwater, groundwater affects geothermal systems, and utility failures can cascade across sectors. These interdependencies mean small thermal changes can produce disproportionate impacts in tightly connected urban environments. Despite growing knowledge of these risks, most cities lack coordinated underground planning, unified thermal management, or robust subsurface data. The researchers call for long-term monitoring networks, early-warning systems, and policy frameworks that treat the subsurface as a strategic resource rather than fragmented engineering projects. Without such reforms, rising underground temperatures may emerge as one of the most underestimated yet consequential challenges for urban resilience in the coming decades.