Exploring nature-based solutions - The role of green infrastructure in mitigating the impacts of weather- and climate change-related natural hazards

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Courtesy of European Environment Agency (EEA)

Natural resource scarcity, climate change impacts, continued employment crises, public budget debts and economic recovery plans are some of the challenges that governments in Europe currently face. Moreover, Member States in the European Union (EU) need to continue building or rebuilding roads, sewage systems, levees, etc. (also known as grey infrastructure). Despite being essential for economic growth, these infrastructure investments are significant and put heavy burdens on governments. But as governments debate the future of economic growth and sustainable development, there is one infrastructure solution that can provide a good return on investment: nature.

In the past, governments and other investors automatically looked to expensive traditional grey infrastructure solutions in order to solve problems. Now, new and in many cases cheaper approaches are emerging that use natural processes or GI rather than concrete and steel. Forests, wetlands and other natural ecosystems are not commonly considered forms of infrastructure. But they are. Forests, for example, can prevent pollutants from entering streams that supply fresh water to cities and businesses downstream. Upstream landscape conservation and restoration measures can act as natural water filtration plants, as an alternative to more conventional water treatment technologies. As such, they are a form of GI that can serve similar functions to grey infrastructure.

For example, pre-existing development of concrete pipes, sewers and particularly of paved surfaces in cities is making it difficult for storm water to be absorbed where it falls. It is becoming increasingly evident that our concrete systems are not always able to accommodate all the storm water that comes their way. This can result in flooding, with tremendous economic and social consequences. Recent work on GI has highlighted the important role ecosystems play in providing benefits to conventional infrastructure solutions. Green areas in cities, for instance, can function as storm-water retention areas and mitigate the load on conventional sewage systems (see Photo ES.1 and ES.2).

Research also shows that in many cases, GI solutions are less expensive than grey infrastructure, and provide a wide array of co-benefits for local economies, the social fabric and the broader environment. This should be of particular interest to decision-makers, as GI can achieve significant cost savings. If GI can provide comparable benefits to grey infrastructure at reduced costs in the long term, then it makes financial sense to invest in the conservation, sustainable management, and/or restoration of natural ecosystems in order to meet development goals.

However, making the financial case for GI is complicated: it can be difficult to make a valid comparison between GI and grey infrastructure with a focus on incurred expenses and benefits. We know that GI solutions often provide multiple benefits (noise reduction, increased carbon sequestration, recreation opportunities, clean water, etc.) that are often cheaper and more robust, not to mention more sustainable, both economically and socially (EEA, 2014). These multiple benefits should be captured in the equation as having positive spin-off effects, while grey infrastructure solutions typically only fulfil single functions such as drainage or transport.

For instance, instead of automatically defaulting to grey solutions like dikes and pipes for flooding, we first should look at restoring floodplains or wetlands. Rather than building sea walls, we need to think about conserving sand banks. And before building more water filtration systems, we might first consider rehabilitating upstream watersheds. Planners should compare green to grey and identify new opportunities for investing in nature, including a combination of green and grey approaches when nature-based solutions alone are insufficient. As planners explore how to accommodate infrastructure demands in the future, the lesson is clear: think about green before investing in grey.

Many countries in the EU have already taken this on board and have prepared national guidance documents and/or strategies to actively encourage investments in GI as an essential part of sustainable spatial planning. GI is increasingly considered a 'life support system' able to deliver multiple environmental functions, with a key role in adapting to and mitigating climate change.

The importance of GI is also recognised in the EU policy domain, as the examples below show.

  • The Seventh Environment Action Programme (7EAP) (Decision No 1386/2013/EU) measures to enhance ecological and climate resilience, such as ecosystem restoration and GI, can have important socioeconomic benefits, including for public health.
  • The EU Biodiversity Strategy (COM(2011) 244 final) calls for a restoration of at least 15% of degraded ecosystems in the EU and aims to expand the use of GI. In addition, the European Commission will continue mapping and assessment work of GI in the context of the Biodiversity Strategy.
  • The 2013 European Commission Strategy on Green Infrastructure (COM/2013/0249 final) (EC, 2013a) underlines that GI can make a significant contribution to the effective implementation of all policies where some or all of the desired objectives can be achieved in whole or in part through nature-based solutions.
  • The Regional Policy 2014–2020 continues to support nature and GI through financial instruments such as the European Regional Development Fund and the Cohesion Fund, which contribute to several policy objectives and deliver multiple benefits, in particular socio-economic development (IEEP and Milieu, 2013).
  • The Water Framework Directive (2000/60/EC), Nitrates Directive (91/676/EEC) and the Floods Directive (COM(2006)15) offer GI-related opportunities (for instance, by supporting actions to put in place GI to improve soil retention, act as buffer strips between agricultural production and water sources, and provide water storage during flood events) (EEA, 2015).
  • The EU Strategy on Adaptation to Climate Change (EC, 2013b) aims to make Europe more climate resilient by ensuring the full mobilisation of GI- or ecosystem-based approaches to adaptation.

GI solutions that boost disaster resilience are also an integral part of EU policy on disaster risk management. Climate change and infrastructure development make disaster-prone areas more vulnerable to extreme weather events and natural disasters such as floods, landslides, avalanches, forest fires, storms and wave surges that cause loss of life and result in billions of euros of damage and insurance costs each year in the EU.
The impacts of such events on human society and the environment can often be reduced using GI solutions, as mentioned above. Functional flood plains, riparian woodland and protection forests in mountainous areas, barrier beaches and coastal wetlands can be set up in combination with disaster reduction infrastructure such as river protection works. Investment in ecosystem‑based DRR and GI can thus provide many benefits for innovative risk management approaches, adapting to climate change-related risks, maintaining sustainable livelihoods and fostering green growth. Cities and local authorities are the first to deal with the immediate consequences of such disasters. They therefore play a critical role in implementing prevention measures like GI.

To address some of these challenges and information gaps, the current report tries to demonstrate the role of GI for mitigating vulnerability to weather and climate variability-related natural hazards at European level. It proposes a simple, practical methodology for screening (rather than assessing) ecosystem services in areas where GI may contribute to reducing current (or future) weather- and climate-related natural hazards. The report addresses landslides, avalanches, floods, soil erosion, storm surges and carbon stabilisation by ecosystems.

As mentioned in Box ES.1, GI is a strategically planned network of high-quality green spaces, which can be approached and defined from different perspectives. In this study, GI is defined by its capacity to provide a relevant number of ecosystem services. The maps presented in this study provide an overview of where specific weather- and climate-related natural hazards are likely to occur, where well-functioning ecosystem services exist which can support DRR and climate adaptation so as to lessen the impacts of natural hazards (e.g. floods and landslides), and where the provision of ecosystem services may be improved.

Regions with well-functioning ecosystem services (depicted in green in the maps) are considered to be part of a GI network that has the main role of mitigating the impacts of climate change natural hazards and/or supporting adaptation to climate change impacts. Those regions exhibiting a lack of mitigating ecosystem services should be considered priority areas for investment in or restoration of the required services, as there is a demand for them expressed by the presence of a natural hazard and assets at risk.

The study identifies two different levels of lack of GI:

  • areas with no or a very low capacity of relevant ecosystem services for the mitigation of a given natural hazard (mapped in red);
  • areas with existing ecosystem services that are not able to function at full capacity (mapped in orange).

For each of the natural hazards assessed in this study, an individual European-scale map of potential GI elements and restoration areas has been produced. For potential restoration areas, stakeholders are requested to take a decision on which areas are to take priority, i.e. whether to restore the partially functioning ones or the non-functioning ones. For example, restoring areas with no relevant ecosystem services for the mitigation of a given natural hazard (mapped in red) might reduce hazard considerably if they are located in an area where the hazard is present.

These decisions might be further supported by considering the demands of population and infrastructure for protection by GI, and an additional series of maps has been produced for that purpose at the Nomenclature of Territorial Units for Statistics (NUTS) 2 level. These maps define 'high-risk areas' at locations where high demand matches with low/ medium-quality GI networks, and where medium demand matches with low-quality GI networks. Such areas are potential priority areas for GI restoration. The resulting 'medium risk area', however, might imply three possible situations: (i) high demand matching high-quality GI implies priority areas for conservation of ecosystems; (ii) medium demand matching medium‑quality GI implies conserving existing GI and at the same time restoring missing GI, and (iii) low demand matching low-quality GI implies that in specific areas, hazard is relevant and GI protection is low, but the overall risk is only medium, due to the current comparably low level of demand.

If risk and demand are high, and ecosystem service capacity for risk mitigation is low, then ecosystem restoration clearly presents a significant and cost-efficient improvement for disaster risk mitigation. However, it should be noted that besides anthropogenic reasons, there are often also natural reasons explaining why a specific area cannot supply relevant ecosystem services.

The ecosystem services (according to the Common International Classification of Ecosystem Services, (CICES, 2015)) classification) were selected based on their potential ability to offer protection against extreme climate-related events:

  • mass stabilisation — landslides
  • mass stabilisation — avalanches
  • flood protection
  • storm surge protection
  • global climate regulation.

The results of the assessment show that it is possible:

  • to use ecosystem services to assess GI;
  • to identify potential areas for conservation and restoration;
  • to identify GI elements as an output of the modelling.

As is to be expected, multifunctional forest ecosystems provide several services addressing the mitigation of most natural hazards. Restoration areas, on the other hand, are often more hazard specific. A central aspect of the study is the coupling of ecosystem services with their demand side in order to identify areas where these services are needed most.

The emerging pattern shows that high-risk areas for landslides mainly occur in hilly to mountainous areas of the Mediterranean and the British Islands. For avalanches, fine-scale high-risk areas could be defined for the Alpine region. Flood risk at NUTS 2 level was greatest in a central European region between western Germany and the Danube Delta, in eastern England, and in parts of central Spain, while storm surge risk was highest at the Northern Sea coasts. The potential GI network for contributions to global climate regulation is mainly defined by a belt of forest spanning northern Iberia to southern France, the southern Alps and parts of the forests on the Carpathians and the Rhodope Mountains.

For future research, it is proposed that the outlook of GI be expanded: from being based on ecosystem services alone, to include other topics such as protected lands, sensitive areas or natural assets as a cornerstone of GI networks to be developed. This obviously depends on the underlying data that have been used to define the GI network. While this study uses ecosystem services, others have used Natura 2000 areas and their connectivity, for instance. Moreover, the selection of ecosystem services influences the outcome of the GI network. Individual GI networks may be developed to support flood protection, water and air quality, biodiversity and migration of species, climate adaptation, etc. All of these GI networks could be 'calculated individually' with the best available data. The results of the different networks (with different purposes) could be combined into a real multifunctional GI network, i.e. a combination of different GI networks can serve a variety of environmental functions.

There are both general and specific limitations inherent in the current work, as described below.

  1. General limitations
    1. The quality of the input data, although generally sufficient, might be regionally different for some of the presented assessments. This can cause biases in the pattern of the result maps.
    2. The selection of climate change-related impacts (natural hazards) that can be moderated by the presence of specific ecosystems and their services. The analysis worked with selected natural hazards which themselves can be moderated by ecosystem services, i.e. if there were no ecosystem services to moderate the hazard, then it was not selected (e.g. forest fire).
    3. The capacity of ecosystems to deliver (good-quality) services is estimated by the condition of the ecosystems.
    4. Some climate change-related impacts are local phenomena which are addressed at European/ landscape scale.
    5. The coarse resolution of three categories for the levels of hazard, vulnerability, GI elements and demand might cause rather different areas to fall under the same category, while close to the categories threshold, small differences might cause a jump to the next category.
    6. Sometimes, the mitigating effect of ecosystem services might be a local phenomenon for which no data are available, e.g. the presence of hedges and tree rows in agricultural areas to combat (wind) erosion.
  2. Specific limitations
    1. Avalanches are particularly local phenomena, and are scarcely assessable at European scale (not in terms of their risk nor their impact). Due to the coarse resolution of the underlying digital terrain model, the threshold for avalanche-endangered slopes needed to be changed with respect to standard literature values (15° instead of 30°), in order to generate relevant risk zones (otherwise, only a few, scattered pixels are defined as endangered).

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