Reducing hydro-meteorological risks with Nature-Based Solutions

Floods, droughts, landslides and heat waves are increasing due to the impacts of climate change. Nature-Based Solutions can be used to effectively reduce hydro-meteorological risk. But what is the best measure to choose? Each area has its specific context for applying NBS, and there are tools to evaluate what is the right action to adopt.

From L. Ruangpan, Z. Vojinovic, S. Di Sabatino, L. Leo, V. Capobianco, A. Oen, M. McClain and E. Lopez-Gunn, Nature-Based Solutions for hydro-meteorological risk reduction: A state-of-the-art review of the research area, paper under discussion for the Natural Hazards and Earth System Sciences Journal. Download the paper here.

Natural hazards are having huge impacts on the global economy and the environment; moreover, climate predictions see further exacerbation of these hazards from human activities (land and water use change, population growth). Effective adaptation strategies, such as the restoration of biodiversity and ecosystem services, are needed to limit risks related to extreme hazards.

What are Nature-Based Solutions?

The European Commission defines NBS as “solutions that aim to help societies address a variety of environmental, social and economic challenges in sustainable ways. They are actions inspired by, supported by or copied from nature […]. Nature-based solutions use the features and complex system processes of nature, such as its ability to store carbon and regulate water flows, in order to achieve desired outcomes […].”

View of the Elbe River (Germany), one of the project demonstrators

There are several types of NBS, bringing different benefits that can be divided into four categories:

· Water management benefits: reducing flood risks, storing and infiltrating rainfall run-off, reducing erosion;

· Socio-economic aspects: a better aesthetic value of the area (increasing tourism, walking, jogging, cycling);

· Economic benefit: reducing damages from hydro-meteorological events, energy saving;

· Environmental benefits: reducing air and noise pollution, creation or rehabilitation of habitats for biodiversity.

Since each NBS is different and improves a particular aspect of an area, they can obtain superior performances when connected together and setted to work in parallel, each treating a different portion of run-off, thereby providing a more robust response to hydro-meteorological events.

NBS can also work combined with grey infrastructures (hybrid solutions), sometimes giving better results than concentrating on one approach only. Studies show that NBS are likely to be more effective when implemented through cooperation with local people, while hybrid solutions are more effective than single NBS in terms of performance.

Illustration of large and small scale Nature-Based Solutions (NBS); Large-scale NBS A illustrates NBS in mountainous regions (e.g., afforestation, reforestation, slope stabilization, etc.), Large-scale NBS B illustrates NBS along river corridors (e.g., dike relocation, retention basins, etc.) and Large-scale NBS C illustrates NBS in coastal regions (e.g., sand dunes, protection dikes/walls, marshes, etc.); Typically examples of Small-scale NBS are green roofs, green walls, rain gardens, porous/permeable pavements, swales, bio-retention, etc.

Good examples of Nature-Based Solutions

Tolbrug Bridge (Room for the River Programme)

An effective example of large-scale NBS implementation is the Dutch “Room for the River Programme”: constituted by 39 local projects based on nine different types of measures, the Programme achieved not only flood risk reduction, but had several co-benefits such as habitat and biodiversity restoration.

Another case study is the Laojiee River Project in Taiwan. The channelized watercourse was changed into an accessible green infrastructure corridor for the public, increasing the recreation activities and the value of the area.

More research is needed to reduce the impact of large-scale hydro-meteorological events and test the efficacy of NBS in rural and natural environments. Three “sister” projects funded by the Horizon 2020 Programme are developing this much needed research on NBS (RECONECT, PHUSICOS and OPERANDUM).

Techniques, methods and tools for planning and evaluating NBS

How does the process for implementation of NBS start? How does an implementer decide on the best NBS to put in place?

First of all, possible measures corresponding to local characteristics are selected. Then, an evaluation of the performance of these measures using numerical models, cost-benefit analysis and/or multi-criteria analysis is needed. In the case of complex systems, optimization can be used to maximize the benefits, while minimizing the costs. All processes are possible to combine in one tool or to use combination of existing tools to select and evaluate NBS.

1) Selection: not all NBS are good for every condition. The choice must be driven by site characteristics, land use, political and financial regulations, amenities, environmental requirements, catchment characteristics and space available.

2) Evaluation: There are several methods to evaluate the performance of NBS:

· Analyse, simulate and model hydraulics and water balance processes. The model results are compared to select the best NBS solution to use.

· Cost-benefit analysis. The analysis is based on the Life Cycle Costing approach (LCC) and the Return on Investment approach (ROI). Benefits considered include the prevention of damage costs, profit losses, erosion damages and agricultural losses, amongst others.

· Multi-criteria analysis, which integrate social and technical approaches to evaluate the performance of NBS. This analysis is useful when there are different and conflicting criteria that must be considered in the decision. Different weights are assigned to each criteria, to create a ranking of measures to choose from. Examples of criteria can be flood mitigation, pollutant removal and aesthetics.

3) Optimisation: parameters to consider when implementing NBS include the number of NBS measures, size, and location. Optimization algorithms can help in deciding suitable combinations, and their arrangements, of NBS measures.

There are tools that can be used for selection, evaluation, and optimization of NBS. These tools have a user-friendly interface and, therefore, simplify the work of the decision makers. Some of the most used tools are:

· Green-blue design tool, PEARL KB, Climate Adaptation App and Naturally Resilient Communities: they permit the user to filter NBS measures in relation to the problem type of the specific area.

· UrbanBEATS: combines both the selection and evaluation processes together.

· BeST Tool, BlueGreen City Toolbox, MUSIC tool: calculate benefits of NBS in monetary as well as in qualitative terms.

Implementations change the appearance of the Thur River (Switzerland)

Socio-economic influence on implementation of NBS

NBS are essential for future socio-economic development. The implementation of NBS is often proposed by an ecologist or biologist and it is often in language or framing that does not resonate with decision makers. This is one of the obstacles that those implementing NBS encounter. How can this be overcome?

Stakeholders and governments need to be more involved in NBS implementations, to raise their awareness of the importance of these measures. Moreover, a lack of confidence in NBS by the public is sometimes observed, a sign that a stronger effort must be made to change public perception. A connected network of joint participation bringing ideas together from municipalities, public works and communities could help to reach the target.

So, not only is it important to involve stakeholders, but it is also necessary to bridge the skills gap between researchers, politicians and financers to be all oriented in the same direction and improve acceptance of NBS measures.