Multidisciplinary evaluation of flood mitigation measures integrating hydrological effectiveness, public perception, economic evaluation and funding opportunities analysis

Climate‑driven changes in flood frequency and magnitude are intensifying the need for robust and efficient flood mitigation strategies that, at the same time, provide ecological co-benefits and are accepted by the public and other relevant stakeholders. A wide spectrum of measures, ranging from conventional grey-structural infrastructure to nature‑based solutions (NbS) and hybrid approaches, is nowadays being considered to reduce hydrometeorological risks. While NbS are increasingly promoted in European and international policy frameworks, their implementation is often hindered by uncertainties regarding effectiveness, feasibility, public acceptance, and funding structures. This contribution provides a brief overview of some recent studies dealing with hydrological modelling, economic evaluation, public perception analysis, and review of funding and conceptual frameworks related to the implementation and design of NbS and other flood mitigation measures.

Public perception study conducted in Slovenia, Czechia, and the Netherlands revealed statistically significant differences in perceived effectiveness, feasibility, and acceptability of green, grey, and hybrid measures. Respondents generally view grey measures such as dams as more effective and acceptable, though more difficult to implement and less feasible, while perceptions varied with country context, age, and income. Additionally, perception of multiple stakeholders was also investigated in Slovenia indicating that researchers tend to rate green measures more favourably compared to engineers and agricultural advisors. For selected measures (dams, retention polders and wetlands) hydrological simulations were conducted in the Gradaščica River catchment in Slovenia. It was shown that wetlands, although offering diverse ecological and other co‑benefits, reduced flood peaks by only few percentages whereas retention polders and dams achieved substantially higher peak flow reductions at reference downstream river cross-sections. Consequently, economic analyses indicated that grey measures outperform green measures in cost‑effectiveness. In contrast, some recently conducted studies showed that other NbS solutions like urban greenery can provide a notable reduction in runoff for low and medium magnitude rainfall events.

A complementary analysis of 53 European funding calls and 342 global projects highlighted how the current NbS policy discourse increasingly shapes funding opportunities and supports framing of interventions as NbS. This framing can facilitate access to resources and significantly enhance the research related to the NbS implementation. However, at the same time, too generic NbS framing can introduce additional uncertainty in assessments of NbS effectiveness and potentially exclude other viable flood mitigation measures from consideration and implementation. Therefore, it is recommended that coherence between the stated NbS and the indicators capturing effectiveness of actual set of measures is critical for gaining evidence from monitoring of hydrometeorological risk reduction projects.

In summary, while NbS and related measures are being promoted by different stakeholders, their public perception, hydrological effects, and economic viability continues to diverge across geographical and institutional settings. The research community, in turn, increasingly labels different types of measures as NbS in order ensure funding, potentially limiting research insights needed for more transparent and effective implementation of NbS.

 

Acknowledgment: The research was conducted within the project J6-4628 (22-04520L) co-funded by Slovenian Research and Innovation Agency (ARIS) and Czech Science Foundation and was additionally supported by ARIS P2-0180 grant.