Nature-based solutions efficiency evaluation against natural hazards: Modelling methods, advantages and limitations

The general patterns of water flow in loess slope system and implications for slope geological security

Loess regions face significant challenges in quantifying hydrological processes and assessing geological environmental risks due to the prevalent development of preferential pathways and the limitations of existing monitoring technologies. To advance this knowledge, this study presents an improved electrical resistivity tomography (ERT) device, specifically designed for loess moisture observations. By refining the testing principle, power supply mode, and data collection method within the existing ERT framework, the new device offers unmanned operation, automatic data acquisition, remote transmission, and cost efficiency. It effectively tracks water movement and groundwater level fluctuations across various hydrological conditions, supporting long-term online monitoring of hydrological processes of loess slopes. Through the analysis of monitoring data and classification of 12 observed preferential flow types, water movement in loess systems can be generalized into four general patterns: uniform infiltration, preferential infiltration, inflowing diffusion, and lateral flow. This generalized scheme provides a simplified modeling approach for other researchers to quantify slope hydrodynamics and to assess geological safety risks involving preferential flow. Based on these insights and field investigations, a conceptual framework is proposed to elucidate the seepage-structure synergistic initiating mechanism of loess landslides. This framework suggests that water entry and movement patterns within the slope depend on the slope geological structure related to preferential pathways and the prevailing hydrological scenarios. Landslide occurs as the result of the progressive failure and reciprocal evolution between the slope hydrological environments and geological structure, which may also pose potential eco-hydrological risks. The outcome advances the development of slope hydrological monitoring technology and enhances the understanding of water movement laws and the associated geological environmental risks in loess slope systems, which is of vital importance to the early warning methods of loess landslides that account for preferential flow and for theoretical modeling of preferential flow in related disciplines.

Pathways of ecosystem-based disaster risk reduction: A global review of empirical evidence

Ecosystems provide valuable services in reducing the risks of disasters through various pathways, which are increasingly recognized as sustainable strategies for disaster management. However, there remains limited information on the underlying ecological processes of risk reduction. This paper addresses this gap by synthesizing ecological mechanisms and evaluating the 'level of evidence' and 'scale of use' through a review of 64 peer-reviewed research articles published between 2015 to 2022. These research articles covered nine types of disasters, predominantly floods (42.19 %), followed by urban heat waves (18.75 %), storm runoff (10.94 %), coastal erosion (9.38 %), tsunamis (4.69 %), and avalanches and landslides (6.25 % each). The level of evidence supporting ecological processes for disaster risk reduction is moderate, as is the 'scale of use'. Results show that there are a few studies describing the mechanism of ecosystem-mediated risk reduction and are mostly limited to the causal relationship. Empirical evidence demonstrates that forest and freshwater ecosystems buffer the risk of urban heat through processes such as transpiration, solar radiation interception, and evaporative cooling, while flood risks are mitigated by enhancing evapotranspiration, reducing water runoff time, and facilitating infiltration rates. Coastal erosion is reduced by dissipating wave energy and through beach nourishment, which facilitates ecological succession. The review underscores that hazard attenuation depends on factors such as forest type (e.g., species composition, age structure, and area), and landscape characteristics (e.g., matrix, composition and configuration). Moreover, the geographic scope of published research is largely confined to developed countries and the global north. Multidisciplinary research involving ecologists and disaster experts is imperative to address existing knowledge gaps and enhance the integration of ecosystem-based adaptation into disaster risk reduction strategies.

What-if nature-based storm buffers on mitigating coastal erosion

Creating ecosystem buffers in intertidal zones, such as seagrass meadows, has gained increasing attention as a nature-based solution for mitigating storm-driven coastal erosion. This study presents what-if scenarios using an integrated model framework to determine the effectiveness and strategies for planting seagrass to reduce coastal erosion. The framework comprises two levels of simulation packages. The first level is a regional-scale coupled hydrodynamic model that simulates the processes of a specific storm and provides boundary forces for the morphodynamic model XBeach to apply at the next level, which simulates nearshore morphological evolution. The framework is applied to the open coast of Norderney in the German Bight of the North Sea. We demonstrate that optimising the location and size of seagrass meadows is crucial to increase the efficiency of onshore sediment erosion mitigation. For a specific depth range, depending on the storm's intensity, the most significant reduction in erosion may not be achieved by starting the meadow at the depth that permits the largest meadow size. To maintain a significant coastal protection effect, seagrass density and stem height should be considered together, ensuring erosion reduction by at least 80 % compared to the unprotected coast. This study provides valuable insights for the design and implementation of seagrass transplantation as a nature-based solution, highlighting the importance of considering location, size, density, and stem height when using seagrass meadows for coastal protection.

Urban heat mitigation by green and blue infrastructure: Drivers, effectiveness, and future needs

The combination of urbanization and global warming leads to urban overheating and compounds the frequency and intensity of extreme heat events due to climate change. Yet, the risk of urban overheating can be mitigated by urban green-blue-grey infrastructure (GBGI), such as parks, wetlands, and engineered greening, which have the potential to effectively reduce summer air temperatures. Despite many reviews, the evidence bases on quantified GBGI cooling benefits remains partial and the practical recommendations for implementation are unclear. This systematic literature review synthesizes the evidence base for heat mitigation and related co-benefits, identifies knowledge gaps, and proposes recommendations for their implementation to maximize their benefits. After screening 27,486 papers, 202 were reviewed, based on 51 GBGI types categorized under 10 main divisions. Certain GBGI (green walls, parks, street trees) have been well researched for their urban cooling capabilities. However, several other GBGI have received negligible (zoological garden, golf course, estuary) or minimal (private garden, allotment) attention. The most efficient air cooling was observed in botanical gardens (5.0 ± 3.5°C), wetlands (4.9 ± 3.2°C), green walls (4.1 ± 4.2°C), street trees (3.8 ± 3.1°C), and vegetated balconies (3.8 ± 2.7°C). Under changing climate conditions (2070-2100) with consideration of RCP8.5, there is a shift in climate subtypes, either within the same climate zone (e.g., Dfa to Dfb and Cfb to Cfa) or across other climate zones (e.g., Dfb [continental warm-summer humid] to BSk [dry, cold semi-arid] and Cwa [temperate] to Am [tropical]). These shifts may result in lower efficiency for the current GBGI in the future. Given the importance of multiple services, it is crucial to balance their functionality, cooling performance, and other related co-benefits when planning for the future GBGI. This global GBGI heat mitigation inventory can assist policymakers and urban planners in prioritizing effective interventions to reduce the risk of urban overheating, filling research gaps, and promoting community resilience.

Fluvial flood adaptation using nature-based solutions: A comprehensive and effective assessment of hydro-meteorological risks

The growing prominence of Nature-based Solutions (NbS) for disaster risk reduction (DRR) has sparked increased interest. This study is motivated by the need to establish a quantifiable and standardized method for assessing the risks mitigated by NbS in engineering applications. The goal is to establish a comprehensive and effective system framework for assessing hydro-meteorological risks related to NbS in engineering applications. The proposed framework considers flood disaster mechanisms, uncertain factors, and ecosystem services, integrating them to comprehensively assess the benefits of NbS. Specifically, 2-D hydraulic analysis and an in-house adaptive Kriging-based reliability analysis are developed and applied to establish flood prevention standards for NbS. Additionally, the InVEST toolkit is utilized to evaluate ecosystem services. To demonstrate the applicability of the framework, the Baoli River Watershed located in Pingtung County of Taiwan is selected as a case study. It is found that NbS can effectively withstand a 25-year return period flood and reduce flooding on agricultural land by 46.03 %. Furthermore, the probability of flooding decreased from 100 % to 27 % for a 20-year return period flood. NbS was found to provide approximately NT$1.20-4.65 million more in total benefit value compared to the engineering governance strategy. The supporting source codes are available at https://github.com/johnthedy/Adaptive-Kriging-Using-PSO-HHs-in-HECRAS3D.git.

Economic assessment of nature-based solutions to reduce flood risk and enhance co-benefits

Flooding is expected to increase due to climate change, urbanisation, and land use change. To address this issue, Nature-Based Solutions (NBSs) are often adopted as innovative and sustainable flood risk management methods. Besides the flood risk reduction benefits, NBSs offer co-benefits for the environment and society. However, these co-benefits are rarely considered in flood risk management due to the inherent complexities of incorporating them into economic assessments. This research addresses this gap by developing a comprehensive methodology that integrates the monetary analysis of co-benefits with flood risk reduction in economic assessments. In doing so, it aspires to provide a more holistic view of the impact of NBS in flood risk management. The assessment employs a framework based on life-cycle cost-benefit analysis, offering a systematic and transparent assessment of both costs and benefits over time supported by key indicators like net present value and benefit cost ratio. The methodology has been applied to the Tamnava basin in Serbia, where significant flooding occurred in 2014 and 2020. The methodology offers valuable insights for practitioners, researchers, and planners seeking to assess the co-benefits of NBS and integrate them into economic assessments. The results show that when considering flood risk reduction alone, all considered measures have higher costs than the benefits derived from avoiding flood damage. However, when incorporating co-benefits, several NBS have a net positive economic impact, including afforestation/reforestation and retention ponds with cost-benefit ratios of 3.5 and 5.6 respectively. This suggests that incorporating co-benefits into economic assessments can significantly increase the overall economic efficiency and viability of NBS.

The underexposed nature-based solutions: A critical state-of-art review on drought mitigation

Droughts are the most expensive climate disasters as they leave long-term and chronic impacts on the ecosystem, agriculture, and human society. The intensity, frequency, and duration of drought events have increased over the years and are expected to worsen in the future on a regional and planetary/global scale. Nature-based solutions (NBS) such as wetland and floodplain restorations, green infrastructures, rainwater harvesting, etc., are highlighted as effective solutions to cope with the future impacts of these events. While the role of NBS in coping with the impacts of other disasters, such as floods, has been extensively studied, there has been a lack of comprehensive review of NBS targeting drought. The following paper provides a unique critical state-of-the-art literature review of individual drought-related NBS around the world, in Europe, and particularly in Belgium, and assesses the critical differences between the NBS applied globally and in Flanders. An extensive literature review was conducted to systematically analyze NBS, listing the type, the location, the status of the implementation, and the possible recommendations proposed to optimize future NBS applications. Finally, a comparison is made between small- and large-scale applications of NBS. By analyzing all these aspects, especially the level of effectiveness and recommendations, insight was gained into the future potential of NBS and possible improvements. The research indicated a lack of scientific publications, especially in Belgium. Hence, grey literature was also included in the literature review. Only four papers included a quantitative assessment regarding the effectiveness of drought on a global level, all stating a positive impact on groundwater recharge. In contrast, at regional and country levels, the performance of NBS was not quantified. The number of large-scale implementations is low, where landscape- or watershed-scale holistic approaches to drought mitigation are still scarce. Some successfully implemented projects are only very local and have a long realization time, two aspects that limit achieving visible impact at a larger scale. Among the many NBS, wetlands are recognized as highly effective in coping with drought but are still degraded or lost despite their significant restoration potential. A common effectiveness evaluation framework shall be followed, which gives policymakers a clear view of the different NBS investment options. Furthermore, a more collaborative approach is recommended globally, including different stakeholder groups, with specific attention to the local communities. To conclude, future research should increase the evidence base and implementation of drought-mitigating NBS.

Nature-based solutions can help reduce the impact of natural hazards: A global analysis of NBS case studies

The knowledge derived from successful case studies can act as a driver for the implementation and upscaling of nature-based solutions (NBS). This work reviewed 547 case studies to gain an overview of NBS practices and their role in reducing the adverse impact of natural hazards and climate change. The majority (60 %) of case studies are situated in Europe compared with the rest of the world where they are poorly represented. Of 547 case studies, 33 % were green solutions followed by hybrid (31 %), mixed (27 %), and blue (10 %) approaches. Approximately half (48 %) of these NBS interventions were implemented in urban (24 %), and river and lake (24 %) ecosystems. Regarding the scale of intervention, 92 % of the case studies were operationalised at local (50 %) and watershed (46 %) scales while very few (4 %) were implemented at the landscape scale. The results also showed that 63 % of NBS have been used to deal with natural hazards, climate change, and loss of biodiversity, while the remaining 37 % address socio-economic challenges (e.g., economic development, social justice, inequality, and cohesion). Around 88 % of NBS implementations were supported by policies at the national level and the rest 12 % at local and regional levels. Most of the analysed cases contributed to Sustainable Development Goals 15, 13, and 6, and biodiversity strategic goals B and D. Case studies also highlighted the co-benefits of NBS: 64 % of them were environmental co-benefits (e.g., improving biodiversity, air and water qualities, and carbon storage) while 36 % were social (27 %) and economic (9 %) co-benefits. This synthesis of case studies helps to bridge the knowledge gap between scientists, policymakers, and practitioners, which can allow adopting and upscaling of NBS for disaster risk reduction and climate change adaptation and enhance their preference in decision-making processes.

Efficacy assessment of green-blue nature-based solutions against environmental heat mitigation

Nature-based solutions (NBS) such as green (vegetation) and blue (waterbodies) infrastructure are being promoted as cost-effective and sustainable strategies for managing the heatwaves risks, but long-term monitoring evidence is needed to support their implementation. This work aims to conduct a comparative assessment of the cooling efficiency of green (woodland and grassland) and blue (waterbody) NBS in contrast to a built-up area. Over a year of continuous fixed monitoring showed that the average daily maximum temperatures at NBS locations were 2-3 °C (up-to 15%) lower than the built-up area. Woodland showed the maximum temperature reduction in almost all seasons, followed by waterbody and grassland. NBS performed the best during the summers, peak sunshine, and heatwave hours (up to ∼ 6 °C cooler than built-up area). Using an e-bike for mobile monitoring, the areas where green-blue NBS were combined showed the highest spatial cooling extent, followed by waterbody, woodland, and grassland areas. The database generated can validate city-scale environmental models and assist city planners to incorporate NBS into urban dwellings based on the opportunity, need and scope, aligning with Sustainable Development Goals 11 (sustainable cities and communities) and 13 (climate action).

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.

Review of Nature-based Solutions in Dryland Ecosystems: the Aral Sea Case Study

NbS have gained substantial attention in the academic literature recently as a potential approach for simultaneously tackling environmental issues and addressing societal challenges. Drylands, which are among the world's most vulnerable areas to the impacts of climate change and cover a little less than the half of the global terrestrial surface, were the focus of this study. We conducted a systematic literature review to explore the potential opportunities for the application of NbS in rural drylands across the globe. We go on to specifically consider the possibility of applying selected NbS approaches in the Aral Sea region of Uzbekistan, as a case study of a dryland ecosystem illustrating major environmental and social challenges. We highlight which NbS show the most promise in the Aral Sea region and conclude with a discussion of existing gaps in the literature on NbS in drylands, and opportunities for further research.

Enabling nature-based solutions: Innovating urban climate resilience

Current conceptualizations of nature-based solutions have so far served to characterize-and reproduce-cost-effective remedies, particularly in cities of the global north. Yet nature-based solutions (NbS) are fundamental to the production of urban resilience. Focusing on Ghana's second largest city, Kumasi, this research (i) examines climate literacy and explores the existing nature-based solutions towards climate change adaption; (ii) examines the perception on existing NbS and the barriers to building climate resilience via NbS; and (iii) explores ways of promoting the implementation of NbS to build climate resilience. It addresses these objectives drawing from secondary data, 367 household surveys and 7 agency interviews. The findings show that about two thirds (63%) of urban residents in the case study area are climate illiterate, and this has affected the slow uptake of nature based solutions as climate management intervention. The urban residents acknowledge the importance of nature based solutions but identify barriers such as poor consideration of the role of natural infrastructure and their incorporation in the planning process, inadequate technical capacity and guidance for incorporating NbS in climate planning, high cost requirements of NbS interventions, disparate interests from various institutions, and a general lack of knowledge, appreciation and interest from urban residents. The study concludes that mainstreaming and upscaling NbS in urban systems will require major investments which should vary from one city to the other depending on perculiar needs.

A modeling application of integrated nature based solutions (NBS) for coastal erosion and flooding mitigation in the Emilia-Romagna coastline (Northeast Italy)

Worldwide, climate change adaptation in coastal areas is a growing challenge. The most common solutions such as seawalls and breakwaters are expensive and often lead to unexpected disastrous effects on the neighboring unprotected areas. In recent years, this awareness has guided coastal managers to adopt alternative solutions with lower environmental impact to protect coastal areas, defined as Nature-Based Solutions (NBSs). NBS are quite popular around the world but are often analyzed and implemented individually at pilot sites. This contribution analyzes the effectiveness of two NBS to mitigate coastal impacts (coastal flooding and erosion) under three historical storms along the Emilia-Romagna coasts and the induced improvements due to their potential integration. Through numerical simulations with XBeach, this study demonstrated that the presence of seagrass meadows of Zostera marina produces an average attenuation of 32 % of the storm peak with a maximum attenuation of 89 % in incoming wave height. Seagrass also mitigates flooded areas and maximum inundation depths by 37 % and 58 % respectively. The artificial dune leads to higher mitigation in terms of inundation of the lagoon (up to 75 %), also avoiding any morphological variations behind it. Seagrass has also been shown to be able to reduce beach erosion volumes up to 55 %. The synergic effect of the two NBS improves the capacity to mitigate both inundation (with a benefit of up to 77 % for flooded area attenuation with respect to cases without any defenses) and coastal erosion. Results of the study suggest that the two NBS will work together to produce co-benefits in terms of preservation of their efficiency, development of habitats for organisms and vegetation species, and thereby offering an important social value in terms of possible tourism, recreation and research.

A nature-based solution selection framework: Criteria and processes for addressing hydro-meteorological hazards at open-air laboratories across Europe

Nature-based solutions (NbS) can be beneficial to help human communities build resilience to climate change by managing and mitigating related hydro-meteorological hazards (HMHs). Substantial research has been carried out in the past on the detection and assessment of HMHs and their derived risks. Yet, knowledge on the performance and functioning of NbS to address these hazards is severely lacking. The latter is exacerbated by the lack of practical and viable approaches that would help identify and select NbS for specific problems. The EU-funded OPERANDUM project established seven Open-Air Laboratories (OALs) across Europe to co-develop, test, and generate an evidence base from innovative NbS deployed to address HMHs such as flooding, droughts, landslides, erosion, and eutrophication. Herein, we detail the original approaches that each OAL followed in the process of identifying and selecting NbS for specific hazards with the aim of proposing a novel, generic framework for selecting NbS. We found that the process of selecting NBS was overall complex and context-specific in all the OALs, and it comprised 26 steps distributed across three stages: (i) Problem recognition, (ii) NbS identification, and (iii) NbS selection. We also identified over 20 selection criteria which, in most cases, were shared across OALs and were chiefly related to sustainability aspects. All the identified NbS were related to the regulation of the water cycle, and they were mostly chosen according to three main factors: (i) hazard type, (ii) hazard scale, and (iii) OAL size. We noticed that OALs exposed to landslides and erosion selected NbS capable to manage water budgets within the soil compartment at the local or landscape scale, while OALs exposed to floods, droughts, and eutrophication selected approaches to managing water transport and storage at the catchment scale. We successfully portrayed a synthesis of the stages and steps followed in the OALs' NbS selection process in a framework. The framework, which reflects the experiences of the stakeholders involved, is inclusive and integrated, and it can serve as a basis to inform NbS selection processes whilst facilitating the organisation of diverse stakeholders working towards finding solutions to natural hazards. We animate the future development of the proposed framework by integrating financial viability steps. We also encourage studies looking into the implementation of the proposed framework through quantitative approaches integrating multi-criteria analyses.

Optimisation of urban-rural nature-based solutions for integrated catchment water management

Nature-based solutions (NBS) have co-benefits for water availability, water quality, and flood management. However, searching for optimal integrated urban-rural NBS planning to maximise co-benefits at a catchment scale is still limited by fragmented evaluation. This study develops an integrated urban-rural NBS planning optimisation framework based on the CatchWat-SD model, which is developed to simulate a multi-catchment integrated water cycle in the Norfolk region, UK. Three rural (runoff attenuation features, regenerative farming, floodplain) and two urban (urban green space, constructed wastewater wetlands) NBS interventions are integrated into the model at a range of implementation scales. A many-objective optimisation problem with seven water management objectives to account for flow, quality and cost indicators is formulated, and the NSGAII algorithm is adopted to search for optimal NBS portfolios. Results show that rural NBS have more significant impacts across the catchment, which increase with the scale of implementation. Integrated urban-rural NBS planning can improve water availability, water quality, and flood management simultaneously, though trade-offs exist between different objectives. Runoff attenuation features and floodplains provide the greatest benefits for water availability. Regenerative farming is most effective for water quality and flood management, though it decreases water availability by up to 15% because it retains more water in the soil. Phosphorus levels are best reduced by expansion of urban green space to decrease loading on combined sewer systems, though this trades off against water availability, flood, nitrogen and suspended solids. The proposed framework enables spatial prioritisation of NBS, which may ultimately guide multi-stakeholder decision-making, bridging the urban-rural divide in catchment water management.

Nature-based solutions for securing contributions of water, food, and energy in an urban environment

There is growing awareness that nature-based solutions (NBS) prevent negative effects and secure ecosystem services. However, the potential of NBS to provide intended benefits has not been rigorously assessed. Water, food, and energy (WFE) are essential for human well-being. This study highlights the importance of NBS in terms of water, food, and energy. A set of on-site NBS that includes permeable pavements, plant microbial fuel cells, bio-filtration basins, and rain gardens is used to determine the contribution of NBS to the environmental and economic development of urban environments. The results of this study show that NBSs benefit an urban environment in terms of water treatment, stormwater retention, food production and energy generation, carbon sequestration, pollination, sedimentation retention, and cultural services dimension. This research highlights an urgent need for the integration of water, food, and energy plans to ensure that NBSs contribute to the environment and for the conservation of ecosystem services.

An integrated assessment of land use impact, riparian vegetation and lithologic variation on streambank stability in a peri-urban watershed (Nigeria)

Bank erosion is an important source of sediment and phosphorus to inland fluvial systems and is generally responsible for more than half of the total watershed sediment export. Numerous studies have quantified bank erosion and the spatio-temporal variation of sediment flux in different watersheds. However, there is sparse research to date on the linkages between bank erosion/accretion and sediment export under different land uses, especially in rapidly evolving peri-urban watersheds. This research, therefore, integrated remote sensing techniques and repeated field survey of erosion pin plots to quantify bank erosion and sediment flux in the 80 km² Nkisi River watershed (NRW), southeast Nigeria, over a three-year period. The impact of land use change on streambank erosion was evaluated by utilising remotely sensed Landsat datasets of 2003, 2010, 2016 and 2019. Geotechnical tests were used to characterise the lithologic properties of the banks, while the Bank Stability and Toe Erosion Model (BSTEM) was used to determine the stability of the banks under various hydrological conditions and mechanical properties of the riparian vegetation. Mean bank recession rates increased from 10.7 cm during the 2017-2018 monitoring period to 17.5 cm for the 2019-2020 monitoring period. The percentage of total watershed export ascribed to bank erosion in the three stream reaches varied from 6.6 to 44.9%. The high rates of bank erosion and accretion within the NRW were attributed to rapid changes in land use, which evolved from grassland and woodland to cropland, built-up and bare land. The BSTEM accurately predicted the high erosion rates of the streambanks and showed that riparian vegetation has a mechanical effect on bank stability. However, the mechanical effect diminishes as the depth to water table rises during high streamflow events.

Comparison of the Engineering Strategies for Low Impact Development in a Densely Populated Old Urban Area

Most old urban areas of China have a dense population, severely indurated underlying surface, and highly developed underground space. Those increase the waterlogging risk and obstruct the stormwater management in old urban areas. To propose an appropriate engineering strategy for low impact development (LID) transformation in an urban area, a simulation was carried out by storm water management model (SWMM) in this project. Bioretention cells, permeable pavements, and green roofs were selected according to the study area surface. Runoff control performance of single LID control and combined schemes were compared. Results illustrate that only 50.21% of roofs can build green roofs in urban areas with dense populations, and the runoff control performance of green roofs is unsatisfactory, while bioretention cells and permeable pavements can effectively mitigate runoff caused by storms with a recurrence period less than 10 years, and combined LID controls can obtain better runoff control performance with less construction area. Those outcomes screened out the LID controls suitable for application in densely populated old urban areas and put forward reasonable engineering practice strategies. This study provides guidance and reference for the LID transformation in the densely populated old urban area.

Hydrological Modeling for Flood Adaptation under Climate Change: The Case of the Ancient Messene Archaeological Site in Greece

There is a growing global awareness about the impacts of climate change on cultural and natural heritage sites. In Greece—a homeland of important historical and cultural resources—archaeological sites are vulnerable to climate change-related flood events. In order to investigate the flood risk of the archaeological site of Ancient Messene under different climate change projections, a physically-based hydrological model was implemented and six climate change scenarios were examined. Additionally, the effectiveness of a soft structural nature-based solution adaption plan was evaluated. Based on the results, the archaeological site of Ancient Messene is shielded against small or larger flood events and only in case of extreme precipitation events is the area likely to be at risk. This flood risk can be further eliminated after implementing the soft structural nature-based solution adaptation plan proposed. Nature-based solutions provide a cost-effective alternative approach for flood risk reduction and climate change adaptation, with minimum possible disturbance, while hydrological modeling, even in case of data scarcity, constitute a valuable tool for flood risk estimation and adaptation plan management. Nature-based solutions seems to be most effective against small or medium precipitation events, and to limit the damages of extreme events. Their benefits for flood adaptation should not be underestimated.