Substantial amounts of waste heat are daily rejected in the urban subsurface
due to anthropogenic activity, underground transport, and subsurface energy infrastructure. This waste heat contributes to subsurface urban heat islands and represents an untapped energy source that can be reutilized in buildings. For the first time, GEOEG assessed Lausanne’s subsurface heat island intensity by determining its sources and effects in order to propose sustainable retrofit interventions and an energy efficiency strategy at the urban scale. The work resorted to temperature measurements in the field and numerical simulations of the thermo-physical state of the subsurface. As a part of this project, a shallow subsurface thermal cadaster was developed for the city of Lausanne, considering both localized and diffused drivers of subsurface urban heat islands, including building basements, district heating networks, and sewer networks.