Policymakers at COP 25 have the opportunity to address and influence policies around infrastructure investments and national development plans. The Zurich Flood Resilience Alliance argues that a move from hazard protection only focused on grey infrastructure to integrated green and grey approaches where nature-based solutions are consistently incorporated is vital to achieve climate-smart, risk informed development. 

What do we mean by Grey and Green infrastructure? 

Grey infrastructure refers to human-made structures using hard building materials. In the case of flood protection this includes barriers, levees, dikes, and dams, often made out of concrete, hence the “grey” label. Green infrastructure consists of more natural solutions and approaches that are multipurpose and aimed at delivering a range of ecosystem services, including, but not limited to, flood protection or resilience. 

What’s the problem with Grey? 

Grey infrastructure usually focuses on a single purpose or benefit only (i.e. a flood wall keeping water away from people and infrastructure) and may not be useful to provide other, more diverse benefits. It also can often provide communities and individuals with a false sense of security. People trust flood barriers to protect them from floods completely, meaning if, or rather when, the barrier fails they are underprepared and struggle to cope with the effects. 

This so called levee-effect also leads to valuable assets or infrastructure such as homes, schools, and even hospitals being built in vulnerable areas, expected to be protected by grey infrastructure when they are in fact not fully protected to the level expected.

Building in these hazardous areas kept “safe” through levees, inhabited by communities unaware of the risk, increases the long-tail risk of flooding: low probability but severe effects. When grey infrastructure fails it often fails colossally, with catastrophic consequences. With evidence that floods are getting more severe as a result of climate change these failures are only going to increase. 

And what’s so great about Green? 

Green (and blue, i.e. ocean) infrastructure, where water is given the space it needs and where areas are left in a more natural state, is smarter – it lacks the thresholds of grey infrastructure, there is no hard overload point at which it fails. Instead the protective benefits are more flexible. It allows for, and promotes, community flood resilience in a way grey approaches do not. Removing the false security provided by flood barriers gives people more opportunities not only to plan and prepare for floods, but to avoid developments in hazardous areas. 

Unlike grey infrastructure green or nature based approaches have benefits far beyond that of flood protection. Climate smart adaptation or disaster risk reduction approaches can provide additional mitigation effects. For example mangroves planted to reduce coastal erosion are also useful in binding CO2. Additionally, green spaces, cleaner air, and access to water provide both mental and physical health benefits to those living in and near it and can reduce summer heat island effects in inner cities. 

One of the strengths of green approaches is that they can be used both as alternatives and complements to traditional, grey infrastructure. It does not have to be one or the other. 

Then why are we still using more Grey? 

One answer is that the cost and benefit of grey structures are easier to calculate, thus easier to fund, than those of green solutions. Human made, grey, infrastructure has a clearer asset life, depreciation, and return on investment. Also, it is easy to directly attribute absence of flooding to hard structures when they work.

It is a bit more complex to factor in the multiple benefits and untapped potential of nature based, green infrastructure, hence the financial case is harder to make. Methods and guidelines for such calculations are still in their infancy, but evolving quickly. It is harder to tell whether a community not being flooded is a direct result of green infrastructure. Additionally, nature based solutions are lacking longer-term track records, lacking the scientific, socio-political, and decision-making buy in required for things to change. 

What needs to change? 

Based on Zurich Flood Resilience Alliance’s cross sectoral expertise in flood resilience and our efforts to implement climate resilient community programmes incorporating climate change and disaster risk management, we urge governments to include the following recommendations in their implementation of national policies and commitments, like the National Determined Contributions (NDCs) and for the private sector to include in Climate Action initiatives like the Coalition for Climate Resilient Investment (CCRI):  

• Promote nature-based solutions when building new infrastructure. Nature-based solutions and green/blue approaches should be the first consideration when implementing integrated climate resilience and risk management approaches. These can replace the need for (or at least complement) grey infrastructure when implementing flood risk reduction. 
• Re-asses the way costs and benefits of grey and green projects and developments are carried out. Factor in the co-benefits beyond flood risk reduction which green infrastructure provides (improved air or microclimate quality, biodiversity, improved water percolation, water quality, erosion reduction, etc.). While also realistically assessing the negative consequences that hard infrastructure such as levees often have and incorporate those consequences fairly and transparently into cost-benefit analyses. Ideally, these new cost-benefit models should also highlight the “cost of inaction” or not investing in ex-ante measures, compared to dealing with the aftermath of flooding.
• Avoid creating new risk (don’t build more assets in hazard-prone areas). This reduces the cost and reduces total risk compared to an approach where new risk is created and (expensive) grey infrastructure has to be built to try to protect these risk prone assets. 
• Nature-based solutions programmes should include a long-term assessment component. There is emerging evidence that ecosystem solutions to protect against natural hazard and to build climate resilience are outperforming grey-only solutions, but a consistent and more comprehensive approach to the assessment is necessary.

In summary, hazard protection infrastructure needs to shift from predominantly focusing on grey prevention structures (dams, levees, dykes) to integrated grey and green approaches where nature-based solutions are consistently incorporated into development planning. COP 25 is a great opportunity for policy makers to get the ball rolling.