Foundations for a future net zero city?

More than 230 local authorities in the UK have declared a climate emergency and, with it, the implementation of climate action strategies to help mitigate and adapt to climate change. However, the city of today isn’t necessarily a useful benchmark to respond to climate pressures: if we are to deliver on our climate and sustainable development goals, a radical rethink of the public realm is needed. 

We talk a lot about the ‘future cities’ in the context of electric vehicles and renewable energy, but I’d like to promote discussion about the use of space beneath our cities to support climate resilience — the so-called final urban frontier.

At first glance, the use of underground space (the subsurface) to support climate action might seem quite an abstract concept, but in reality there are already several inspiring examples where the application of science, innovation and technology are delivering novel subsurface land uses in support of climate resilience. This includes Growing Underground in London, turning a former Second World War bunker into an energy-smart ‘urban farm’ for microgreens, and the storm-water management and road tunnel (SMART) in Kuala Lumpur, which doubles up to provide storage for storm water during extreme rainfall.

In the future, will we also see the first underground park (the Lowline in New York) in aid of urban greening and cool spaces? Or the repurposing of old shafts for gravity energy storage? Or perhaps the movement of goods underground as per the Swiss cargo sous terrain? And of course, there are more established technologies that are already being applied across cities in the UK such as sustainable drainage systems (SuDS) to help manage flood risk and ground source heat pumps, which provide a low carbon energy source to heat and cool down buildings — two active research areas for scientists at the BGS.

There is much to be optimistic about, but we must be cautious. The geology (the subsurface ground conditions) of UK urban centres is highly variable and has a significant bearing on what underground technologies and innovations can be successfully implemented.

Ground conditions will affect the design of underground schemes, have an impact on the cost of construction below ground and will influence the financial viability of the development. For example, infiltration SuDS can only be installed where the ground is permeable enough to receive the surface water and where there is no risk of mobilising contaminants in the ground or exacerbating existing ground risks. Open-loop ground source heat pumps can only be installed where there is a source of groundwater to circulate through the system, where the thermal properties of the ground are suitable and if the system won’t negatively impact the environment or surrounding land uses.

BGS has been conducting research over a number of years to characterise urban subsurface environments to support land-use planning and help identify where these new climate measures and technologies can be implemented.

Our 3D and 4D models provide an enhanced understanding of the geological structures and sediments and the physical properties of the ground in urban areas. These geological models are being used to support the use of geothermal energy sources in Glasgow and Cardiff, the construction of new tunnels in London and subsurface planning in Singapore.

We have urban observatories that monitor changes in the environment associated with the implementation of climate measures and new technology, for example monitoring changes in temperature or changes in the water system. We have recently published outcomes from our SuDS observatory, which investigated changes in soil moisture and groundwater recharge processes through infiltration SuDS. The research recommends the use of hybrid infiltration and water retention SuDS schemes to effectively manage flood risk.

With a robust ground model for the urban subsurface and a good appreciation of geological properties and processes we can more confidently implement environmentally sensitive design principles and edge closer towards the climate resilient city.

Stephanie Bricker

BGS Urban Geoscience team leader

BGS Keyworth

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