The knowledge gap database compiles an evidence base for Nature-based Solutions, to support defining research and innovation avenues, and bolster policy and practitioners’ knowledge and knowledge-implementation. This database, first published in 2021 and updated in June 2024, aggregates knowledge gaps and research needs identified through extensive desk research, drawing from academic and non-academic sources. For a detailed explanation of the methodology and analysis behind the 2024 update, please refer to this NetworkNature report. For more context on the initial database see the NetworkNature report on practical, research, and innovation needs.
The updated database includes additional 619 gaps categorised into 32 broad topics and 11 types of approaches. This marks a significant expansion from the initial database, established in 2021, which contained 172 knowledge gaps. Covering gaps from 2017 to March 2024, this database will be continually updated throughout the duration of NetworkNature+.
| Gap description | Origin of source | Source | Resource | Broad topic | Types of approaches | |
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| In addition, co-creating change has shown to be necessary but insufficient for success in some reported case studies. Thus, it remains necessary to evaluate how power dynamics influence equity and the outcomes of NbS. | Desk Study | Scientific literature | Palomo, Ignacio & Locatelli, Bruno & Otero, Iago & Colloff, Matt & Crouzat, Emilie & cuni sanchez, Aida & Gómez-Baggethun, Erik & González-García, Alberto & Grêt-Regamey, Adrienne & Jiménez-Aceituno, Amanda & Martín-López, Berta & Pascual, Unai & Zafra-Calvo, Noelia & Enora, Bruley & Fischborn, Marie & Metz, Rosmarie & Lavorel, Sandra. (2021). Assessing nature-based solutions for transformative change. One Earth. 4. 10.1016/j.oneear.2021.04.013. |
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| As demonstrated by the bibliometric analysis, however, issues of justice remain underexplored within the literature. This points towards the need for developing just nature-based solutions and bringing together conceptual clarity on how to achieve just outcomes through NBS. | Desk Study | Scientific literature | Cousins, Joshua. (2020). Justice in nature-based solutions: Research and pathways. Ecological Economics. 180. 10.1016/j.ecolecon.2020.106874. |
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| Future research could engage more diverse, including marginalised groups, in the assessment of social acceptability to better understand ‘whose values’ rather than what values and where are likely to be affected by different biodiversity conservation and climate mitigation and adaptation strategies. This approach reflects current calls for just processes in urban green transitions for climate neutrality and biodiversity enhancement. | Desk Study | Scientific literature | Raymond, C.M., Lechner, A.M., Havu, M. et al. Identifying where nature-based solutions can offer win-wins for carbon mitigation and biodiversity across knowledge systems. npj Urban Sustain 3, 27 (2023). https://doi.org/10.1038/s42949-023-00103-2 |
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| Additional research is needed to comprehensively address core design aspects of NBS intended to mitigate urban heating, including factors such as the abundance, distribution and type of green and blue spaces, the micro-climatic thermal benefits of planting densities and specific species of trees and other vegetation, and social acceptability, local preferences and the integration of NBS within a built environment of high cultural heritage value. | Desk Study | Scientific literature | Calliari, Elisa & Castellari, Sergio & Davis, Mckenna & Linnerooth-Bayer, Joanne & Martin, Juliette & Mysiak, Jaroslav & Pastor, Teresa & Ramieri, Emiliano & Scolobig, Anna & Sterk, Marjolein & Veerkamp, Clara & Wendling, Laura & Zandersen, Marianne. (2022). Building climate resilience through nature-based solutions in Europe: A review of enabling knowledge, finance and governance frameworks. Climate Risk Management. 37. 100450. 10.1016/j.crm.2022.100450. |
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| Issues of NBS spatial and temporal scale and extent of cooling effect similarly require further investigation to inform the establishment and scaling of NBS across urban areas. | Desk Study | Scientific literature | Calliari, Elisa & Castellari, Sergio & Davis, Mckenna & Linnerooth-Bayer, Joanne & Martin, Juliette & Mysiak, Jaroslav & Pastor, Teresa & Ramieri, Emiliano & Scolobig, Anna & Sterk, Marjolein & Veerkamp, Clara & Wendling, Laura & Zandersen, Marianne. (2022). Building climate resilience through nature-based solutions in Europe: A review of enabling knowledge, finance and governance frameworks. Climate Risk Management. 37. 100450. 10.1016/j.crm.2022.100450. |
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| Longer-term research, including modelling and spatial analyses, data collection and observations, as well as the application of comparative approaches and data sharing, is necessary to identify patterns and meta-level strategies to support urban planning and development focused on mitigating excess urban heat. | Desk Study | Scientific literature | Calliari, Elisa & Castellari, Sergio & Davis, Mckenna & Linnerooth-Bayer, Joanne & Martin, Juliette & Mysiak, Jaroslav & Pastor, Teresa & Ramieri, Emiliano & Scolobig, Anna & Sterk, Marjolein & Veerkamp, Clara & Wendling, Laura & Zandersen, Marianne. (2022). Building climate resilience through nature-based solutions in Europe: A review of enabling knowledge, finance and governance frameworks. Climate Risk Management. 37. 100450. 10.1016/j.crm.2022.100450. |
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| In this vein, understanding the interactions between the solution and the medium it has been introduced in is an important platform to consider. Often, NBaS are wrongfully introduced as immune systems without considering how the components of the ecosystems they were introduced into influence their survival/efficiency. | Desk Study | Scientific literature | Mario J. Al Sayah, Pierre-Antoine Versini, Daniel Schertzer, H2020 projects and EU research needs for nature-based adaptation solutions, Urban Climate, Volume 44, 2022, 101229, ISSN 2212-0955, https://doi.org/10.1016/j.uclim.2022.101229. |
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| Given the predominant focus on ecosystem service outcomes, which emphasize biophysical impacts rather than social ones, the limited evidence on equity was expected. Nevertheless, there remains a critical need for more impact evaluation studies generally and specifically for those that attend to issues of equity. | Desk Study | Scientific literature | Castle, S.E., Miller, D.C., Merten, N. et al. Evidence for the impacts of agroforestry on ecosystem services and human well-being in high-income countries: a systematic map. Environ Evid 11, 10 (2022). https://doi.org/10.1186/s13750-022-00260-8 |
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| Quantitative and spatially explicit data are needed to support the development of mountain-specific policies and governance, however these data are mostly lacking in many mountain regions worldwide. | Desk Study | Scientific literature | Uta Schirpke, Genxu Wang, Emilio Padoa-Schioppa, Editorial: Mountain landscapes: Protected areas, ecosystem services, and future challenges, Ecosystem Services, |
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| Future research should focus on exploring the hydrological characteristics of other infrastructures to enhance the understanding of their overall performance in urban water management. | Desk Study | Scientific literature | Wenjie Chen, Weiqi Wang, Chao Mei, Yisi Chen, Pingping Zhang, Peitong Cong, Multi-objective decision-making for green infrastructure planning: Impacts of rainfall characteristics and infrastructure configuration, Journal of Hydrology, Volume 628, 2024, 130572, ISSN 0022-1694, https://doi.org/10.1016/j.jhydrol.2023.130572. |
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| We need on- farm type research and farms that can serve as demonstration sites and ideally whole watersheds (catchments) where the putative best combinations of techniques are used and evaluated for multiple years in real-world settings. | Desk Study | Scientific literature | Kronberg, S.L. & Provenza, Frederick & van Vliet, Stephan & Young, Sierra. (2021). Review: Closing nutrient cycles for animal production – Current and future agroecological and socio-economic issues. Animal. 15. 100285. 10.1016/j.animal.2021.100285. |
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| Our study reveals that rigorous evidence on the effects of agroforestry interventions remains extremely limited. Impact evaluations of agroforestry interventions remain challenging due to the long time scale between implementation and impacts. The scope of many development projects usually only lasts a few years, so long‐term monitoring and evaluation must be built in to project proposals and designs. | Desk Study | Scientific literature | Miller, Daniel & Ordonez, Pablo & Castle, Sarah & Forrest, Samantha & Nava, Noé & Hughes, Karl & Baylis, Kathy. (2019). The impacts of agroforestry on agricultural productivity, ecosystem services, and human well‐being in low‐and middle‐income countries: An evidence and gap map. Campbell Systematic Reviews. 16. 10.1002/cl2.1066. |
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| We need to better understand the costs and benefits of agroforestry from an interdisciplinary perspective, incorporating economics, social science, and environmental science, to assess its viability as a conservation practice while also considering the needs of farmers. | Desk Study | Scientific literature | Miller, Daniel & Ordonez, Pablo & Castle, Sarah & Forrest, Samantha & Nava, Noé & Hughes, Karl & Baylis, Kathy. (2019). The impacts of agroforestry on agricultural productivity, ecosystem services, and human well‐being in low‐and middle‐income countries: An evidence and gap map. Campbell Systematic Reviews. 16. 10.1002/cl2.1066. |
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| The lack of evidence on agroforestry interventions underscores the need for more high‐quality impact evaluation studies that use experimental or quasiexperimental designs. Impact evaluations of agroforestry policies, programs, and projects implemented on farmers land are urgently needed to help us understand what types of interventions work, under what circumstances, and with what effects for different objectives and social groups. Such studies should assess effects on the range of relevant outcomes along the causal chain, including agricultural productivity, ecosystem, and human well‐being outcomes. | Desk Study | Scientific literature | Miller, Daniel & Ordonez, Pablo & Castle, Sarah & Forrest, Samantha & Nava, Noé & Hughes, Karl & Baylis, Kathy. (2019). The impacts of agroforestry on agricultural productivity, ecosystem services, and human well‐being in low‐and middle‐income countries: An evidence and gap map. Campbell Systematic Reviews. 16. 10.1002/cl2.1066. |
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| To support the use of NbS in the understudied societal challenges, causal evidence is needed and can be achieved through new research using new data, with the implementation of longitudinal studies. To identify mechanisms for the use of NbS in the health sector, innovative research strategies could include collaborations between health specialists, urban planners and engineers, to conduct randomised, controlled NbS trials to considerably reduce the risk of bias and thereby provide stronger proof for the efficiency and impact of NbS. | Desk Study | Scientific literature | Dunlop, T., Khojasteh, D., Cohen-Shacham, E. et al. The evolution and future of research on Nature-based Solutions to address societal challenges. Commun Earth Environ 5, 132 (2024). https://doi.org/10.1038/s43247-024-01308-8 |
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| Under this context, significant efforts are needed for the assessment of large scale NBS-NBaS, watershed scale NBS-NBaS and hybrid structures that contain both small and large NBS. | Desk Study | Scientific literature | Mario J. Al Sayah, Pierre-Antoine Versini, Daniel Schertzer, H2020 projects and EU research needs for nature-based adaptation solutions, Urban Climate, Volume 44, 2022, 101229, ISSN 2212-0955, https://doi.org/10.1016/j.uclim.2022.101229. |
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| The complexity of the environmental challenges and the solutions themselves calls for significant efforts that are still somewhat underdeveloped, particularly in the domain of assessing the changes brought about by the (re)introduction of “nature” and its processes into a specific ecosystem. Accordingly, there is a need to develop tools that take into consideration the interconnectivity of the natural and newly inserted system. | Desk Study | Scientific literature | Mario J. Al Sayah, Pierre-Antoine Versini, Daniel Schertzer, H2020 projects and EU research needs for nature-based adaptation solutions, Urban Climate, Volume 44, 2022, 101229, ISSN 2212-0955, https://doi.org/10.1016/j.uclim.2022.101229. |
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| The monitoring and evaluation frameworks for NBS, like the EU Handbook, are available but there is a need to identify and utilise appropriate metrics and indicators to assess the socio-ecological effectiveness and limitations of NBS in the face of future climate change. | Desk Study | Scientific literature | Sisay E. Debele, Laura S. Leo, Prashant Kumar, Jeetendra Sahani, Joy Ommer, Edoardo Bucchignani, Saša Vranić, Milan Kalas, Zahra Amirzada, Irina Pavlova, Mohammad Aminur Rahman Shah, Alejandro Gonzalez-Ollauri, Silvana Di Sabatino, Nature-based solutions can help reduce the impact of natural hazards: A global analysis of NBS case studies, Science of The Total Environment, Volume 902, 2023, 165824, ISSN 0048-9697, https://doi.org/10.1016/j.scitotenv.2023.165824. |
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| Social-ecological benefits need to be evaluated in a holistic, geographical context. Building a systematic model including all the essential components in a social-ecological system is advocated so that any change in a particular factor reveals the associated responses of both ecological and social benefits in the restoration program. | Desk Study | Scientific literature | Fu, Bojie & Liu, Yanxu & Meadows, Michael. (2023). Ecological restoration for sustainable development in China. National Science Review. 10. 10.1093/nsr/nwad033. |
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