• Energy Efficiency
  • Climate Change
  • Sustainability

Nature-Based Solutions: Evolving from Grey to Green

Oct 12, 2022

Guidehouse Insights Sustainability

Coauthored by Kelly Dong, Liv Gwilliam, Ted Kowalsky, and Emma Krause

Engineering has been a predominant mechanism by which humans have sought to shape, channel, and control the capricious powers of the natural world. Grey infrastructure—dams to harness the power of our rivers, seawalls to push against shoreline erosion and ocean tides, and levees to protect communities from flooding—have been hallmarks for how humans use engineering to protect and benefit societies. However, changes in the predictability of our environment are testing the boundaries of grey infrastructure.

Increasing climate-induced natural disasters are costing governments substantial amounts of money as they’re forced to repair and rebuild grey infrastructure that cannot always subsist against growing climate threats. By 2021, major US weather events accounted for a cumulative cost of $145 billion. Between 1980 and 2020, weather and climate-related extremes in Europe accounted for around 80% of total economic losses, amounting to EUR 487 billion (~$473 billion). These repeated events and repair cycles have a compounding effect, stressing grey architecture and public spending to their limits. 

What Are Nature-Based Solutions?

As a result, the climate community has begun to reassess humans’ approach to managing natural systems.  Governments and communities are exploring whether alternative methods might prove more effective than traditional grey strategies, including methods such as nature-based solutions (NBSs).

NBSs work in conjunction with traditional built environments and consider whether natural solutions could enhance existing strategies to mitigate climate effects and build more resilient communities. Through sustainable design and engineering practices, NBSs leverage natural features in built environments to create greater climate resilience and provide additional environmental and health benefits to local communities. NBSs such as roof gardens, permeable pavements, and urban forests that absorb water can be climate friendly, socially responsible, and economically viable infrastructure solutions.

Benefits of NBSs include: 

  • Flexible adaptation to continued climactic changes without additional infrastructure development
  • Reduction in greenhouse gas (GHG) emissions associated with implementation
  • Increased responsiveness to local community feedback and needs
  • Increased cost effectiveness (by one estimate, NBSs could be as much as 50% cheaper than traditional grey infrastructure) 
Enhancing Grey Infrastructure with NBSs

The importance of understanding and employing NBSs alongside grey infrastructure has never been more prominent. NBSs offer an opportunity to shape the natural environment in ways that mitigate or avoid the risks and emissions of traditional engineering. For instance, concrete, one of the biggest producers of GHG emissions, is frequently used in grey infrastructure. Traditional infrastructure often eats into natural beaches and shorelines, disrupting local ecosystems, affecting native wildlife, and paradoxically leading to increased shoreline erosion. 

In the US, following the aftermath of superstorm hurricane Sandy in 2012, New York State proposed a 6-mile seawall to protect lower Manhattan and portions of New Jersey, with an estimated timeline of 25 years and cost of $119 billion. Experts suggest that this solution may ultimately not mitigate climate threats in 25 years and the New York seawall may be obsolete even before the final ounce of concrete is poured. 

In contrast, a grey-green solution to rehabilitate the Serchio river basin in Italy is underway to reduce the risk of floods and droughts in a Mediterranean catchment while increasing biodiversity and improving water quality. A human-made diversion channel for excess water is being built and coupled with several NBS techniques including buffer strips with plants designed to stabilize the soil and reduce runoff of sediments and pollutants from nearby agricultural fields; a sediment retention basin; and water plants designed to clean sediment from the water supply before it flows into a nearby lake.  Projects like this one are increasingly being proposed, developed, and implemented. 

Although grey infrastructure solutions will continue to play a part in climate adaptation, NBSs present an enormous opportunity for government entities to manage the effects of climate change and promote resiliency and the wellbeing among countries, states, and local communities.