Subsurface planning: Towards a common understanding of the subsurface as a multifunctional resource

In response to powerful trends in technology, resource and land supply and demand, socioeconomics and geopolitics, cities are likely to increase use of the subsurface in the near future. Indeed, the subsurface and its appropriate use have been put forward as being of crucial importance if we are to achieve resilient and sustainable cities. In recent years, quite apart from being seen primarily as a construction basis to provide physical space for infrastructure and to create a better surface living environment, the subsurface has been recognised as a multifunctional natural resource, one which provides physical space, water, energy, materials, habitats for ecosystems, support for surface life, and a repository for cultural heritage and geological archives. Currently, the subsurface is often utilised according to the “first-come-first-served” principle, which hinders possibilities to take strategic decisions on prioritisation and optimisation of competing subsurface uses, as well as fair inter- and intragenerational distribution of limited natural resources. Taking a broad international perspective, this paper investigates the subsurface as a multifunctional resource from five focal points: (1) what professionals with different backgrounds mean when using different terms related to the subsurface; (2) how professionals describe the subsurface and its multiple resources, functions and services; (3) how planning of subsurface use is supported in policy and regulations; (4) how the subsurface is included in the planning process; and (5) frameworks that can support decision-making on responsible use of the subsurface. The study reveals that the subsurface must be recognised (not only by scientists but also by decision- and policy-makers and other stakeholders) as a precious and multifunctional resource requiring careful planning and sensitive management in accordance with its potential and its value to society. Utilisation of the different subsurface functions to yield services requires careful planning and a framework to support decision-makers in achieving a balance between utilisation and preservation, and between the subsurface functions themselves in the case of outright utilisation. Further, to facilitate the necessary change towards transdisciplinary work settings in the planning process and form a platform for knowledge exchange and capacity building, there is an urgent need for a common language, i.e. mutually understandable terminology, and a common understanding, i.e. an all-inclusive view on the subsurface as a complex multifunctional resource.