Ex-ante evaluation of NbS effectiveness in mitigating water-related hazards at a catchment level

Nature-based solutions (NbS) draw researchers’ attention as they can offer numerous co-benefits to the society and environment, as opposed to the traditional grey infrastructure, while having a potential to offer the same level of protection against water-related hazards, such as floods. Therefore, NbS are deemed a viable option to climate change adaptation. However, proof of their effectiveness in mitigating water-related hazards, especially at a large-scale level (i.e., at a catchment level), are still lacking. Ex-ante assessments, which are needed for initiating NBS projects, heavily rely on the modelling, mainly hydrological and/or hydrodynamical. The effectiveness of NbS is quantified through modelling exercises, by comparing simulated hazard levels simulated with- and without an NbS implemented. However, these assessments of NbS effectiveness are fraught with uncertainties, which primarily stem from the way they are accommodated in the models. Specifically, there are no clear guidelines on inclusion of NbS in the models, and evaluation of their effectiveness.

To learn about modelling of the NbS effects on reducing water-related hazards, a survey was distributed among the RECONECT (http://www.reconect.eu/) participants. The survey contained questions about the NbS and water-related hazards considered, and on the details on the models employed to simulate NbS effects, as well as on the indicators used to gauge NbS effectiveness. In most cases, flood hazard was considered, while the respondents reported various NbS (e.g., retention ponds, flood plain restoration, afforestation and reforestation). The respondents indicated that the NbS were included in the models by (1) changing model parameters (e.g., to represent afforestation or reforestation), (2) by including additional computational elements in the model (e.g., storage-type elements that represent retention ponds), or (3) by changing simulation settings to represent hydraulic structure operation. The way in which NbS are modelled was also dictated by the features of the model used. In some instances, some NbS could not be modelled, since they act at rather small-scale, and their effects could not be captured by a model (e.g., check dams in the headwater parts of a catchment). The respondents reported various indicators, but those related to flood hazard was most frequently reported one. Generally, all respondents agreed that the NbS modelling remains a great challenge, and that specific guidelines are needed.

To facilitate bridging this gap, a new survey on modelling of NbS effectiveness in reducing water-related hazards is launched. The new survey focuses on the “water” aspect of the NbS effectiveness, and delves into specific details on the model development and application. The main goal of this research is to target a wider audience (such as audience at EGU), and facilitate sharing knowledge on modelling of the NbS effects. It is the authors’ firm belief that sharing knowledge on modelling of NbS effectiveness can promote their wider implementation, and aid sustainable mitigation of water-related hazards, and adaptation to climate change.

 

Acknowledgements

This research received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No. 776866 for the research RECONECT (Regenerating ECOsystems with Nature-based solutions for hydro-meteorological risk rEduCTion) project.