Research articleIdentifying barriers for nature-based solutions in flood risk management: An interdisciplinary overview using expert community approach
Graphical abstract
Introduction
The recent major flood that hit vast regions of Belgium, the Netherlands, Germany, and Austria reminds society that floods are recurrent and among the costliest natural hazards in Europe (Cornwall, 2021, MunichRe, 2021). Despite the existing flood risk management (FRM) strategies and initiatives implemented over the last decades, flood hazard is expected to increase in some European regions due to climate change (Blöschl et al., 2019; IPCC, 2021) and increasing human pressure on river systems (Hein et al., 2016; Ferreira et al., 2018; EEA, 2018).
The long-term FRM efforts relying on technical measures to prevent and mitigate floods have shown to be not sufficiently effective (Ellis et al., 2021) and to have some adverse environmental impacts (Xu et al., 2021). Indeed, the implementation of technical measures can cause unintended consequences that lead to increased exposure of societal assets, denoted as the safe development paradox (Haer et al., 2020), or may negatively affect floodplain connectivity and its ecological functions (Keesstra et al., 2020; Jakubínský et al., 2021). Therefore, FRM strategies have recently shifted towards solutions that use nature-derived features, processes and management options to improve water retention in catchments and floodplains (Jakubínský et al., 2021). Nature-Based Solutions (NBS; Kabisch et al., 2016; Hartmann et al., 2019a, Hartmann et al., 2019b, for definitions of overlapping terms) are measures and actions that are inspired and supported by natural processes, although their implementation and maintenance may also require technical interventions. The intended function of these measures range from reducing runoff and instream flow by water storage, to de-synchronizing spatio-temporal patterns of peak flows during extreme hydrological events. For settings such as urban landscapes with limited availability of land to retain water, NBS are also combined with engineered infrastructure to form hybrid solutions (Alves et al., 2020). However, regardless of the setting, a catchment-wide perspective is essential to mobilise co-benefits of various NBS and to support water sensitive spatial planning (Hartmann, 2018; Albrecht and Hartmann, 2021).
While there is an increasing number of initiatives and projects implementing NBS worldwide and the reviews of NBS effects for enhancing ecosystem services are available (Jones et al., 2012; Kabisch et al., 2016; Keesstra et al., 2018), there is a persisting lack of empirical data documenting the effectiveness and efficacy of NBS in FRM at various spatiotemporal scales (Dadson et al., 2017; Ellis et al., 2021). In addition, the existing evidence from the implementation of NBS in FRM is rather fragmented and with contrasting results, leading to a lack in wider policy considerations (Wingfield et al., 2019). These factors limit our understanding of suitable design and implementation of different types of NBS in various environmental and institutional settings.
The research on effects and implementation barriers of NBS is mostly diverted in the two following avenues employing different concepts, epistemologies and methodologies. First, for hydrological processes, the evidence on effects related to NBS is mainly collected through ongoing field experiments and modelling (e.g., Ferreira et al., 2020; Nicholson et al., 2020). Second, for the policy domain, the research has mostly focused on developing new planning instruments, negotiation approaches and stakeholder engagement schemes (e.g., Bark et al., 2021; Zingraff-Hamed et al., 2021). This drives an urgent need to adopt an integrated approach for exploring the cascading and compound interactions among various implementation barriers related to NBS and their combinations. Moreover, as the empirical evidence is poorly validated and it will take considerable time to provide more robust results, expert-based approaches should be employed to inform policy- and decision-makers in using NBS for FRM.
This paper aims to identify the barriers of NBS for FRM based on an expert community approach, which has been successfully employed for understanding complex problems across fields (e.g., Elliot et al., 2020). More specifically, we identify experiences with the preferred NBS in European regions and document the spectre of barriers that impair their wider implementation. Based on this evidence, we identify knowledge gaps and formulate research directions to streamline and facilitate further studies of NBS for FRM. Adding up to the existing NBS in FRM reviews (e.g., Dadson et al., 2017; Wingfield et al., 2019; Keestra et al., 2020; Ellis et al., 2021), we extend our focus on both the urban and rural settings and their interactions, and on the implementation barriers emerging at the intersect of hydrology and soil sciences, on the one hand, and land use planning, social geography and economics, on the other. We draw upon the four years of the Cost Action initiative entitled LAND4FLOOD Natural flood retention on private land (https://www.land4flood.eu), which has established an interdisciplinary community of researchers and practitioners.
Section snippets
Data and methods
The research has been conducted in three phases (Fig. 1), allowing to refine the methodological design upon internal and external discussions and to ensure consistency in the contributions by experts involved in the survey.
The first phase involved establishing an interdisciplinary group of experts (https://www.land4flood.eu) based on academia and conducting collaborative research with practitioners. The expert community discussions conducted enabled drafting a research design for this study and
Types of NBS
The list of NBS (Table 1) obtained during the initial expert workshop showed that there is no common understanding of whether NBS denote only physically-based nature-derived measures. The results indicate that NBS should be understood as a broader ensemble of measures and practices that would also include (i) artificial measures supporting nature-based processes as well as hybrid measures combining technical and green interventions, such as dry polders, and (ii) management approaches, such as
Conclusions
Current policies and strategies increasingly highlight NBS as suitable approaches to FRM. This paradigm shift is supported by empirical evidence that remains rather fragmented. In addition, an increasing number of studies point out NBS limitations to effectively enhance water retention and reduce flood risk, and report various implementation barriers for NBS across Europe and beyond. In this paper, we scrutinized the research devoted to implementation barriers of NBS by conducting discussions
Funding
The networking of authors was funded by COST Action LAND4FLOOD (CA16209) supported by COST (European Cooperation in Science and Technology, www.cost.eu) and complementary national InterCost Project (MŠMT LTC18025). N. Bezak and M. Šraj work was partially supported by the Slovene Research Agency (ARRS) through grant P2-0180 and conducted in the scope of the UNESCO Chair on Water-related Disaster Risk Reduction.
Author contributions statement
P. Raška, N. Bezak, C.S.S. Ferreira and Z. Kalantari: research design, data curation, drafting the paper. All authors contributed to data collection, commented on and approved the final paper. All authors understand that the Corresponding Author is the sole contact for the Editorial process.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We are greatly indebted to colleagues, who participated the initial workshop and discussions: Karin Snel, Simon McCarthy, Thomas Kahlix, Alaoui Abdallah, Valentina Nikolova, Aleksander Glavinov, Mila Chilikova-Lubomirova, Mikhail Kalinin, Dimmitra Manou.
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