A financing gap is seen as a crucial barrier, hampering the further uptake and upscaling of Nature-based Solutions (NbS). However, it is not always clear what is meant by this, nor is it clear why this barrier exists and persists. The aim of this paper is to generate an enhanced understanding of financial barriers to NbS. This is accomplished through first conceptually and theoretically clarifying the difference between funding and financing and then exploring these through an integrative literature review. We expose three different dimensions of financial barriers in NbS projects, namely the occurrence of multiple types of funding gaps, the occurrence of multiple types of financing gaps, and the particular and complex cost structures of NbS. NbS funding gaps can be broken down into public funding gaps, private funding gaps, and funding gaps specific for lifecycle phases, activities, and cost types. Bridging the funding gap is a necessary (although not sufficient) condition for bridging the finance gap and financing alone cannot solve a funding problem. We further find that these different dimensions of financial barriers can be explained by the misalignment between the characteristics of NbS and the characteristics of our existing institutions. These misalignments occur through different institutional mechanism, including (i) Funders’ preferences, (ii) Revenue generation enablers, (iii) Justification requirements, (iv) Funders’ regimes, (v) Financiers’ preferences and (vi) Finance application processes. All mechanisms influence the occurrence of public and private funding and financing gaps and they influence the cost structure of NbS, in particular transaction costs. The results of this analysis suggest that overcoming NbS funding and financing challenges requires a systemic, multi-level approach as the barriers to project implementation are not all located within a project's sphere of influence or control.

Increased climate impacts threaten coastal functions globally, highlighting the need for multifunctional coastal climate adaptation. Sand nourishment can adapt sandy coasts to sea level rise, mitigate erosion, increase flood safety, enhance ecological habitats and expand recreational space. Therefore, sand nourishment is increasingly regarded as a promising nature-based strategy for coastal climate adaptation. However, despite this growing recognition, the assessment of how sand nourishment design impacts multifunctional adaptation remains limited. In this perspective article, we argue for three key lessons for researchers to optimise assessing multifunctional coastal climate adaptation by sand nourishment. We conducted stakeholder workshops to scope and inform our perspective, performed semi-structured literature reviews to concretise and validate this for international applications, built a qualitative model to visualise our interdisciplinary overview of how nourishments impact coastal multifunctionality, reflected on this in expert workshops, and identified implications for researchers. In this manner, we assessed the effects of nourishment design on coastal morphology, ecology, socio-economics and ecosystem services in realising the key policy goals of flood safety, nature and recreation. We found that sand nourishment design can result in conflicts between policy goals, generate ambiguous outcomes and lead to system-wide feedback effects. As such, we identified three key lessons: (1) conflicts between policy goals require informing political decision-making on prioritisation between coastal functions, (2) concreteness is needed on otherwise ambiguous functions, and (3) ongoing, multidisciplinary system-wide monitoring is essential. We thus call for a holistic approach to sand nourishment design and encourage researchers from diverse expertise and localities to expand on and adapt our findings to optimise informing sand nourishment design for delivering multifunctional coastal climate adaptation worldwide.

The community value and resonate with some species and ecological systems more than others and therefore can be used to engender broader public support for nature positive outcomes. Yet many of these are not the scientifically-derived indicator species or ecological communities used by conservation scientists to determine and report on the pressures or condition of the environment nor by those implementing programs or actions needed to reverse biodiversity loss. Urban environments represent the intersection of two complex systems, human and natural, and yet this socio-ecological or coupled human-natural system nexus remains elusive within conservation law and policy and the dominant paradigm of grey infrastructure in cities. New approaches are needed to tether environmental policies and practices, such as nature based solutions, to the values and interests of individuals and their place. This article offers a novel framework through which nature-based solutions may achieve policy traction when tied to iconic species that the community value. The iconic species framework is founded on validity theory and the relevance of community-selected species in supporting nature positive outcomes. In parallel, the framework satisfies the data driven outcomes on which science and conservation policy relies upon and the use controls that direct nature-based rather than conventional engineering approaches. The iconic species framework is situated between the indicator species framework, whereby taxa are selected on the basis of their ecological sensitivity, and flagship species, that are largely emblematic. It links numerous ecological and environmental requirements of the species that are preferred by the community to develop nature-positive policy and practice outcomes.