A critical review of Natural Flood Management application and spatial prioritisation approaches in tropical island catchments

Tropical island communities face substantial hydrometrological threats, including flood inundation. Flood risk is increasing, driven by climate change but also other factors including urbanisation, land-cover and land-use (LCLU) change, making flood management challenging to address in practice. Protecting, restoring, and emulating the natural functions of catchments to reduce flood risk, also known as Natural Flood Management (NFM), is a promising method for improving flood management. Global NFM research is in its infancy and NFM research in tropical island states has tended to focus on individual catchment projects. Therefore, overall trends, challenges, and opportunities for NFM in tropical island catchments are poorly understood and, until now, have not been reviewed across these geographies. A particular gap in NFM understanding in tropical island catchments is how NFM options can be best implemented within any particular catchment - specifically where NFM should be located, how modelling can support these decisions and the influence of different catchment characteristics on these decisions. This literature review aims to explore what, where and how NFM has been used in catchments in tropical island states, with a specific focus on catchment characteristics and spatial modelling. This paper draws on research and interconnections between multiple environmental science spheres, by reviewing both academic and grey literature to better understand how NFM has been applied in tropical island states, with a primary focus on Pacific Island Countries and Territories (PICTs). The research highlights that some islands have greater potential for exploiting NFM due to their physical catchment characteristics and data availability. NFM spatial modelling approaches need to be further developed and adapted to specific tropical island community requirements to improve inland flood resilience at the pace needed and to ensure resources are directed optimally.

Embedding nature-based solutions into the social cost of carbon

China, the world's largest CO₂ emitter, is making every effort to transition to a low-carbon economy and fulfill its part of a concerted global commitment to combating climate change. In tandem with decarbonizing energy and industries, feasible supplementary measures are urgently needed to help remove anthropogenic CO₂ from the atmosphere. A burgeoning literature has emphasized the CO₂ removal capability of land re-naturalization (such as afforestation and wetland restoration), thereby regarding cognate land-use conversions as Nature-based Solutions (NbS) and potential climate policy options. However, little empirical evidence exists concerning the effectiveness of different land re-naturalization pathways (such as converting wetlands to forests or agricultural lands to grasslands), and it also remains unclear how NbS alternatives (i.e., land-use conversions resulting in negative CO₂ emission) and non-NbS options (i.e., land-use conversions resulting in positive CO₂ emission) could affect the social cost of carbon (SCC), a conventional measurement for prescribing carbon mitigation approaches. This study aims to fill in this knowledge gap via embedding NbS into the dynamic integrated climate-economics (DICE) model to quantify their impacts on the SCC. Using the Pearl River Delta region (south China) as a case study for the temporal horizon during 2000-2020, we find that both positive and negative CO₂ fluxes have been brought by different natural/semi-natural land conversions, affecting the SCC correspondingly. A total of 7 out of 17 types of land-use conversions could be identified as feasible NbS interventions, including forest restoration, forest-to-wetland, grassland-to-forest, grassland-to-wetland, grassland-to-cropland, cropland-to-forest, and cropland-to-wetland conversions, which could reduce the SCC values (comparing 2020 base-year with 2000 base-year) by 0.0132, 0.0009, 0.0033, 0.0030, 0.0001, 0.0082, and 0.0001 (USD/tCO₂), respectively. While the SCC is mainly determined by energy and industrial structure, the overall effect of NbS is larger than the sum of land urbanization and non-NbS land-use conversions. Via embedding the real-world inter-dynamics of land-use conversions into the SCC quantification, this study presents a pioneer assessment of the impacts of NbS on the SCC in an integrated framework, sheds important insights into the effectiveness of NbS, and offers practical implications for policy-makers to devise comprehensive policies covering all feasible CO₂ abatement options.

The role of Nature-based Solutions in disaster resilience in coastal Jamaica: current and potential applications for 'building back better'

Jamaica, like most Small Island Developing States around the world, is at high risk of coastal hazards due to its exposure to tropical storms, high levels of coastal development, vulnerable coastal communities, and the predicted impacts of climate change. Environmental degradation has been linked to increased vulnerability to disasters. Nature-based Solutions, although not formally present in the literature, are being implemented at various scales in Jamaica. This paper presents an overview of three marine and coastal Nature-based Solutions being utilised in the country: protected area management (Special Fishery Conservation Areas); mangrove restoration; and coral restoration. The paper briefly reviews their current application in Jamaica before arguing that these conservation projects that traditionally focused on biodiversity have co-benefits as Nature-based Solutions for disaster resilience. The paper closes by outlining several research objectives that should be explored in the future to further the implementation of Nature-based Solutions for disaster resilience in Jamaica.

Co-design of experimental nature-based solutions for decentralized dry-weather runoff treatment retrofitted in a densely urbanized area in Central America

The quality of water in many urban rivers in Latin America is increasingly degrading due to wastewater and runoff discharges from urban sprawl. Due to deficits in sanitary drainage systems, greywater is discharged to the stormwater drainage network generating a continuous dry-weather runoff that reaches rivers without treatment. One of the main challenges in the region is to achieve sustainable management of urban runoff for the recovery of rivers ecosystem integrity. However, retrofitting conventional centralized wastewater drainage networks into the existing urban grid represents important social, economic and technical challenges. This paper presents an alternative adaptive methodology for the design of Nature-based Solutions for decentralized urban runoff treatment. Through this study, technical solutions commonly used for stormwater management were adapted for dry-weather runoff treatment and co-designed for the particular conditions of a representative study area, considering space availability as the main constraining factor for retrofitting in urban areas. The application of a co-design process in a dense neighbourhood of the Great Metropolitan area of Costa Rica brought to light valuable insights about conditions that could be hindering the implementation of NBS infrastructures in Latin America.