The evolution and future of research on Nature-based Solutions to address societal challenges

Nature-based Solutions (NbS) are actions to protect, sustainably manage, and restore natural and modified ecosystems to address societal challenges while providing human wellbeing and biodiversity benefits. NbS have historically focused on resource management and ecosystem function but are increasingly framed as responses to the climate emergency, disaster risk, and biodiversity loss. The International Union for Conservation of Nature (IUCN) identifies seven societal challenges NbS can address: climate change mitigation and adaptation; disaster risk reduction; economic and social development; human health; food security; water security; and reversing environmental degradation and biodiversity loss. This study aims to systematically map and analyse NbS research from 1990–2021, identify primary thematic clusters, assess how these align with the seven societal challenges, evaluate their evolution over time and geography, and propose pathways to address gaps—particularly where societal needs and research production are misaligned with global vulnerabilities.

Previous NbS reviews have often targeted specific contexts or issues (e.g., hydrobiodiversity, social justice, human wellbeing) using a mix of automated text mining/machine learning and desktop reviews. Few have comprehensively assessed the entire NbS research landscape with an explicit focus on the breadth of IUCN societal challenges and on access/coverage across regions. The paper notes increased NbS funding and scholarship since 2015 (aligned with the UN SDGs and Paris Agreement), and highlights the need for systematic, large-scale mapping to identify trends and gaps beyond climate and biodiversity foci.

- Data source: Web of Science Core Collection (1900–present). Searches executed on 25 March 2022, restricted to 01/1990–12/31/2021. - Search strategy: Preliminary search using only the term “nature-based solution” was too narrow. The final strategy compiled umbrella terms closely aligned with the NbS concept (e.g., Nature-based solutions, Ecological restoration, Green infrastructure, Ecosystem restoration, Ecological engineering, Urban greening, Ecosystem-based approach, Engineering/Building with nature, Ecosystem-based adaptation, Natural infrastructure, Working with nature/natural processes, Soft engineering). Terms inherently tied to a single challenge (e.g., ecosystem-based disaster risk reduction) were excluded to avoid bias. The final Boolean query combined terms with OR in title/abstract/keywords, yielding 16,290 unique publications (citing articles). - Document co-citation analysis (DCA): Bibliographic data were analysed with CiteSpace to identify frequently co-cited references and thematically cluster the field. Seventeen major clusters (each with 150–1200 cited references and >200 citing articles) were retained; smaller clusters were excluded. Clusters were labelled using burst terms and verified via title review of cluster papers. - Assignment of societal challenges: The seven IUCN societal challenges were manually assigned to clusters by reviewing abstracts, introductions, and conclusions (not full texts). Two clusters focused on governance/implementation rather than a specific challenge and were tagged as governance (an eighth category for this study). Sensitivity analysis assessed impacts of alternative assignments. - Temporal comparison: For each 4-year period from 1990–2021, the presence of clusters associated with each societal challenge was tallied and expressed as percentages to reveal shifts over time, including a focused analysis for the NbS era (2009–present). - Geographic analysis: Author affiliations per country/continent were tallied (counted once per country per paper) to map research production and the proportion of affiliations per continent for each societal challenge. These were contrasted with regional vulnerability indices (e.g., Gini, Prosperity, Global Food Security, Global Water Security) to identify mismatches and priority regions. - Keyword analysis: VOSviewer was used to identify top author keywords per country for nations with the highest proportion of affiliations (excluding terms denoting themes or specific economy/sector/location identifiers). - Sensitivity analyses: A narrower DCA using only “Nature-based solutions” (2009–2021) produced themes consistent with those from the broader umbrella-term dataset for that period, indicating robustness of thematic results.

- Research concentration: 14 of 17 identified clusters primarily addressed climate change impacts/adaptation/mitigation and biodiversity loss, indicating strong concentration on these foundations. - Understudied challenges: Four societal challenges are peripheral across the NbS landscape—economic and social development, human health, food security, and water security. Up to end of 2021, these were often intertwined within other clusters and were the principal focus in only one cluster (air quality/health, cluster 17) among the 17 themes. - Temporal evolution: Early work (1990–2000) focused on ecological engineering, forest/ecosystem restoration—precursors to NbS. Post-2015 growth in NbS research (aligned with UN SDGs and EU Horizon programs) expanded themes such as disaster risk reduction (clusters 5, 6, 8). Human health (clusters 6, 17) and water security (cluster 8) emerged but remained relatively low compared to other clusters. - Geographic distribution: Research production is dominated by Europe and North America, with substantial output also from China, Australia, and Brazil. These distributions correlate with major funding sources (e.g., EU Horizon) and national policy/funding contexts. - Vulnerability mismatch: The highest vulnerabilities in the understudied challenges often lie outside Europe and North America, yet research outputs are skewed toward those regions, underscoring a need to reassign priorities and include local researchers in vulnerable regions in stewardship and authorship. - Thematic pathways: Six research pathways are proposed to advance NbS research: Maintain (foundational themes and policy integration), Expand (integrate interdependencies across challenges), Pilot (field trials and long-term monitoring), Innovate (novel designs, causal evidence, materials), Re-assign (align priorities with regional/global vulnerabilities; include local agendas), Connect (link legacy literature/terminology to NbS).

The study addressed its core question by systematically mapping NbS research themes, their alignment with IUCN societal challenges, temporal evolution, and geographic distribution relative to vulnerability indices. Findings confirm that the field predominantly targets climate change and biodiversity loss, while economic and social development, human health, food security, and water security remain underrepresented. This imbalance, alongside regional mismatches between research production and vulnerability, implies that current NbS scholarship may not fully meet societal needs where they are most acute. The proposed six pathways outline actionable strategies to: sustain and translate foundational evidence into policy; broaden project objectives to capture interdependencies (e.g., water–energy–food nexus); strengthen empirical, context-specific evidence via pilots; generate causal evidence through innovative, interdisciplinary designs (e.g., randomized controlled trials for health-related NbS); reassign research efforts toward high-vulnerability regions and include local researchers in governance and authorship; and connect past domain-specific literatures to the NbS framework to expand the evidence base. Collectively, these actions aim to realign NbS research with global social-ecological priorities, enhance interdisciplinary impact, and support equitable, resilient outcomes.

NbS research has expanded rapidly, particularly since 2015, but remains concentrated on climate and biodiversity themes. The study reveals persistent gaps in the four understudied societal challenges—economic and social development, human health, food security, and water security—and highlights geographic mismatches between research production and vulnerability. By identifying 17 thematic clusters and comparing them across time and regions, the paper provides a comprehensive map of the NbS landscape and proposes six research pathways (Maintain, Expand, Pilot, Innovate, Re-assign, Connect) to guide future efforts. These recommendations encourage prioritizing research in vulnerable regions, integrating multiple societal objectives, building causal evidence, and linking legacy knowledge to the NbS concept. Future work should invest in long-term, interdisciplinary, and context-specific research programs, include local stewardship and authorship, and target integrated solutions that support environmental, societal, and economic goals.

- Data source scope: Reliance on Web of Science Core Collection may omit relevant publications from other databases or grey literature. - Search term choices: Exclusion of some domain-specific terms to avoid bias toward single challenges could under-represent certain literatures; inclusion of umbrella terms may also shape cluster composition. - Co-citation clustering and labelling: Cluster labels were derived from burst terms and manual title reviews; subjective interpretation may influence theme naming. - Societal challenge assignment: Manual assignment based on abstracts/introductions/conclusions (not full-text reviews) may introduce classification uncertainty; sensitivity analyses suggest limited impact on overall conclusions. - Geography via affiliations: Using author affiliations as a proxy for research origin does not always reflect study locations or beneficiaries. - Cluster coverage: Only clusters with sufficient size were included; smaller or emerging themes may be underrepresented.