Nature-based solutions knowledge gaps

NbS projects have shown to reproduce and increase existing inequalities or even create injustices. Also, NbS capacity building and financing risks to do the same at a larger, inter-city or inter-regional scale.

One of the pre-eminent challenges in the implementation of NbS is simultaneously managing multiple socio-ecological objectives including maximization of (1) biodiversity (e.g., native species, species richness, endangered species); (2) regulating services (e.g., flood and erosion control, wildfire management, pest outbreaks), and (3) cultural services (e.g., recreation space, aesthetic landscapes, spaces for quiet and reflection). Such management requires a transdisciplinary approach that engages natural and social scientists, land use managers, non-governmental environmental organizations, and local residents, among others, in order to define and integrate multiple - potentially conflicting - perspectives and goals. What is needed is a well-structured, yet adaptable, socio-ecological assessment framework which applies methodologies to integrate scientific knowledge and objectives with public perspectives and.

Questions were raised during the workshop regarding approaches on how to involve stakeholders from planning administrations and residents in long-term projects, as well as if all residents can benefit from implemented NbS or if benefits are only accessible to a selected portion of the population

Remaining knowledge gaps and a lack of comprehensive evidence on the reversibility, flexibility, cost-effectiveness and feasibility, and/or long-term sustainability of NbS as compared with grey approaches are barriers to mainstreaming of NbS and their full incorporation within (re)insurance schemes.

Researchers and practitioners have good understanding of the environmental impacts of NbS, but it remains unclear as to whether specific actions are cost effective and give rise to a range of benefits. This gap points to the need to better understand the interface between environmental, economic and social dimensions of NbS. Interdisciplinary, mixed‐method research designs that balance the need for qualitative and quantitative assessment of NbS impacts are missing from the NbS literature. Assessments which balance these are crucial to appreciating and understanding the complex linkages between elements of the socio‐economic, socio‐cultural systems and ecosystems.

Second, appraisals rarely factor in trade-offs among different interventions and ecosystem services, or between stakeholder groups, which may experience the costs and benefits of NbS

So far, most projects have investigated the effects of NbS on microclimate, while the susceptibility of NbS to extreme events has been neglected and requires further research. How is climate change foreseen to impact ecosystem health and individual species across the EU?

Societal relations also concern knowledge gaps relating to the identification of an optimal way of communicating positive and negative examples (failures) of NbS.

The assessment of NbS effectiveness or impacts is a multi-scale and multi-temporal problem. Indicators for urban scales and issues may not be relevant for wider scale such as catchment basin scale for example when dealing with flood risk reduction.