The hidden role of the subsurface for cities

The evolution of cities is directly linked to their subsurface: the local geology and hydrogeology alongside the history of human interventions are the basis for the present structure and organisation of cities and affect the prospects for future developments within and above the ground. The underground serves multiple purposes in cities including; providing stability for buildings, providing drinking water and materials, serving as a heat source or retention basin, and accommodating infrastructure and developments. In the face of growth predictions and climate change, interdependencies between urban planning objectives and the subsurface, such as placing infrastructure underground to release surface congestion, remediation of brownfields for development, or prospecting for geothermal energy, become ever more important. This paper reviews current initiatives in industry, policy and research in the UK, which aim for changes in urban subsurface management and governance. It identifies the multitude of planning topics in which the subsurface implicitly features, many of which are commonly only addressed at project level. It highlights that the wider impact of these interventions on underground space and the development of the city is not considered. Consequently, the value of the subsurface for sustainable and resilient development of cities may not be realised