“Nature-based solutions” is a term for all solutions that use the natural world to mitigate the effects of climate change. It sounds rural, but the phrase covers multiple possibilities, from tree planting to soak up carbon emissions to flood protection through providing more green space – and so is increasingly used to provide effective and cost-effective solutions in cities too.

The way urban nature-based solutions can work, says Dr David Tyler, EBRD Associate Director and water sector specialist, is by providing “a softer approach to the hard-engineered conventional solution – one which is arguably also cheaper, but has added benefits, too, particularly in terms of amenity and introducing nature.”

Media interest in nature-based solutions has grown since they became a campaign issue in the run-up to the UK presidency of the COP26 global climate summit, due this November.

Among the adventurous early projects now being conceptualised are several in the parts of the world where finance is provided by the EBRD, a development bank at the forefront of climate finance, which operates around central and eastern Europe, Central Asia and the southern and eastern Mediterranean region – notably in some of the 47 cities already working to improve their sustainability through the innovative EBRD Green Cities programme.

The idea of this EUR 3 billion programme is to help each member city identify, prioritise and tackle the challenges it faces in becoming more sustainable, through a tailor-made programme of improvements drawn up with the support of EBRD experts. (The thinking behind the programme is that cities, where an ever higher proportion of the world’s population choose to live, are the source of three-quarters of greenhouse gas emissions, and thus an important focus of climate action.)

Where nature-based solutions come into this planning, Tyler says, is in providing new answers to questions such as, “how can a city increasingly plagued by heavy rainfall, which brings localised flooding that can endanger lives, deal most sensibly with it?” The conventional urban-planning wisdom is to collect and convey away water pouring down from rooftops through a network of underground pipes. But as cities grow, drawing all that water away through an ever-increasing network of pipes is a very expensive approach. As Tyler says, “the wisdom increasingly is to bring in more sustainable urban development solutions – a way of including nature in planning and design.”

An effective nature-based solution is to manage excessive rainwater through localised solutions ranging from green roofs, artificial basins, grass embankments to ponds with reeds that capture and use the rainwater as the first line of defence against flooding. These are called Sustainable Urban Drainage Systems, Tyler explains: “When it rains heavily, the water is attenuated in these green pockets, and stored locally. Once the storm is over, the water will seep back gradually into the conventional system in a more controlled way”.

The beauty is all in the simplicity. A water retention pocket might be as basic as, say, a small patch of green land, containing an artificial pond with reeds, between blocks of flats. They often have the added benefit of being more aesthetic – softer in appearance, with the plants providing micro-habitats for small animals, birds and insects.  

One example Tyler cites of a city that could benefit from this approach is Varna, in Bulgaria, which joined EBRD Green Cities in June 2019 and began consultations on its Green City Action Plan soon afterwards. One focus has been the rehabilitation of key segments of Varna’s water infrastructure, strengthening the city’s climate resilience and improving resource efficiency.

“They have this problem with rainwater running down the streets causing severe localised flooding. Conceptually this is the type of solution we are imagining for Varna.”

“We talked two years ago about whether they were interested in sustainable urban draining systems and now we are actively considering these types of solution – a softer engineered approach that works in partnership with existing systems, using green features within urban environments.”

Another flood-prone member city of EBRD Green Cities is Chisinau, the capital of Moldova. Here the solution being examined is to re-engineer the River Bic, reintroducing more natural features along its edges to help control the combined effect of river and storm water more sustainably.

“Rainwater from streets ends up in rivers and when those rivers are also surcharged the risk of flooding is high. Here the idea is to deliberately slow down the path of the river, by looking at the catchment and where flooding occurs … introducing something that is more natural in combination with traditional flood defences.”

Managed realignment is another option in flood management. One in London is located on the outer reaches of the River Thames, protected by a river barrier in the huge estuary that goes eastward to Essex – but now with a more natural area too, where “the UK Environment Agency very cleverly deliberately broke the defence in front of the Thames barrier, and have created an area of natural habitat that intentionally floods when there’s a sea surge – only maybe once every year or two – which is now part of a series of natural defences for London.”

“This is what Chisinau is thinking of, too – a park that might occasionally flood, but in a place where you want it to flood rather than trying to push the problem away by building canals or, worse, letting the city flood,” says Tyler, adding that urban planners were being lined up to “help understand how we can reengineer natural features to protect the city and also create public amenity space.”

A third way of controlling stormwater and river flooding is being considered in the Albanian capital Tirana, where the city administration plans to develop an orbital forest, initially by persuading local citizens to donate individual trees. The orbital forest is to be located partly within Tirana’s floodplain where high river water spills over:

“When the river is flowing in wet conditions, the trees will slow the flow of water and, in a similar way to that embankment, add protection and reduce the risk of flooding in the city. By growing an orbital forest you also improve air quality – a dual benefit. The third component is that it’s a very nice natural feature, which is where I understand the Mayor has been engaging with the community to sponsor planting trees.”

While the natural benefits of these plans are clear and intuitive, the idea of nature-based solutions is so new that ways of working out how to count and cost such investments are still being developed. Questions under consideration include how to measure the benefit, and demonstrate whether a nature-based solution works better than a conventional engineering solution, as well as whether such investments might be paid for by the city in question through a small tax rise, Tyler says:

“How do you value the benefit of a solution? We have to do a bit of extra work on that. Developing this work is requiring us to think differently about how to demonstrate the value proposition. The value is difficult to monetise.

A way of measuring, for instance, flood protection measures is to count how much money a city saves if there is less flooding after the measures are introduced, he adds. “In case of a flooding solution, you’d establish the frequency of flooding and who is impacted. Then you’d understand the cost of that impact on people and commerce. With a flood protection scheme, you measure the reduced flood risk, more importantly the cost of avoiding flooding.”

The added benefit of a nature-based solution – the value to public amenity of creating an attractive green space – is also difficult to put a monetary value on. “We are including that in our solution, so we are having to work a bit differently. There’s a lot of evidence that this can be a cost-effective way forward. But we’re talking here about engineering work which still needs managing and maintaining, but is different to conventional infrastructure. We have yet to fully understand how to invest in that kind of infrastructure.”

This is where the consultation process each city undergoes as it draws up its tailor-made Green City Action Plan (GCAP) within the EBRD Green Cities process is especially helpful, Tyler says, as it allows each member city to explore nature-based solutions that have worked elsewhere in the world and, if appropriate, adapt them. “We won’t always find a nature-based solution, but if there is a legitimate, cost-effective, multiple-benefit approach then we should be promoting it. It may be new to us, but these solutions have been well rehearsed and well tested elsewhere in the world. We need to use the GCAPs in a deliberate way to tease out opportunities.”

Source: EBRD