Integrated assessment of existing practices and development of pathways for the effective integration of nature-based water treatment in urban areas

Green roof effects on urban building surface processes and energy budgets

Nature-based solutions are increasingly used in domestic wastewater treatment, because of their potential to remove contaminants and pathogens from water (e.g., stormwater, river water, wastewater) as well as their provided co-benefits, such as mitigation of the heat island effect or enhanced biodiversity. The transition from traditional grey technologies towards nature-based solutions in domestic wastewater treatment might yield multiple benefits for local communities while enhancing biodiversity. Although some nature-based solutions such as treatment wetlands have been used for decades in domestic wastewater treatment, this is not the case for others such as green walls or roofs, which lack implementation guidelines and design criteria. Aiming to support implementation of nature-based solutions in domestic wastewater treatment, we have developed an online decision-support system for the pre-selection of the best nature-based solution to use in each socio-environmental context and adapted to the needs, as well as an estimate of the required area. Our decision-support system's recommendations are based on an expert knowledge-driven approach, building on two complementary expert knowledge elicitation workshops. We hope the developed online decision-support system will support the transition towards integrating nature-based solutions into urban water and wastewater treatment systems.

<p>In the recent past, severe flooding have caused major natural disasters leading to severe damage to public property, infrastructure and human life. The threat of flooding can be attributed to rapid growth in population, uncontrolled urban expansion, global warming and climate change. It has been reported that more than 100,000 people were killed and over 1.4 billion people were affected worldwide due to flooding over the past ten years. The main contributing factors of flooding that affect death or injury to people include flood depth, velocity of flood flow and the degree to which people are exposed to flood in the region. A significant increase in rate of flooding occurred due to decrease in vegetation cover and increase in the imperviousness at urban areas, leading to decrease in the efficiency of urban drainage system that increase proneness of flooding. This study identifies an innovative approach to flood control by deployment of a Nature based solution (NBS). NBS is relatively new approach to tackle flooding and is a solution framed with an inspiration and support from nature. This research focuses on addressing the following three questions: which NBS to deploy, how to identify the ideal site for deployment of the selected NBS, and how to quantify the effectiveness of the deployed NBS in terms of flood control/reduction? As a part of the EU Horizon 2020’s OPERANDUM project, the case study is being conducted at Dublin as the Open Air Laboratory Ireland. The NBS implementation study has been initiated along with the partnership of Dublin City Council. Preliminarily, city planning rules and land development guidelines were reviewed from Dublin and green roof was selected as the potential NBS. Subsequently, rainfall-runoff based hydrological modelling was performed to assess the potential flood hazard areas and to identify an effective location for implementation of NBS. For this purpose, the hydrological model was simulated with and without the presence of NBS at different potential locations and the site exhibiting highest flood control was selected to be the optimal location. The selected location is close to the Dublin Port and adjacent to River Liffey, which is the main river in Dublin. In order to show the effectiveness of the green roof NBS, real world data has been collected before and after implementation of the NBS to assess its effectiveness in real world framework.</p>

Sub-Saharan Africa (SSA) is the region most vulnerable to climate change and related hydro-meteorological risks. These risks are exacerbated in rapidly expanding urban areas due to the loss and degradation of green and blue spaces with their regulating ecosystem services. The potential of nature-based solutions (NBS) to mitigate hydro-meteorological risks such as floods is increasingly recognized in Europe. However, its application in urban areas of SSA still needs to be systematically explored to inform and promote its uptake in this region. We conducted a multidisciplinary systematic review following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) protocol to establish the general patterns in the literature on NBS and hydro-meteorological risk mitigation in SSA. We searched scientific journal databases, websites of 12 key institutions and 11 NBS databases and identified 45 papers for analysis. We found at least one reported NBS in 71 % of urban areas of SSA across 83 locations. 62 % of the papers were clustered in South Africa, Kenya, Tanzania and Nigeria only, while the most studied cities were Dar es Salaam and Kampala. Moreover, 66 NBS practices were identified, most of which (n=44) were for flood mitigation. With only Mozambique (n=2) reporting NBS among the most at-risk countries, we found that NBS are implemented where risks occur but not where they are most severe. Mangrove restoration and wetland restoration, reforestation and urban forests, and agroforestry and conservation agriculture were the most common NBS practices identified for floods, extreme heat and drought mitigation, respectively. Traditional practices that fit the definition of NBS, such as grass strips and stone bunds, and practices more popular in the Global North, such as green roofs and green façades, were also identified. These NBS also provided ecosystem services, including 15 regulatory, 5 provisioning and 4 cultural ecosystem services, while 4 out of every 5 NBS created livelihood opportunities. We conclude that reported uptake of NBS for hydro-meteorological risks in SSA is low. However, there could be more NBS, especially at the local level, that are unreported. Furthermore, NBS can help SSA address major development challenges such as water and food insecurity and unemployment and help the sub-region develop climate-resiliently. We, therefore, recommend that NBS be mainstreamed into urban planning and for knowledge exchange opportunities between SSA and Europe and other regions to be explored to promote uptake.

Sub-Saharan Africa (SSA) is the region most vulnerable to climate change and related hydro-meteorological risks. These risks are exacerbated in rapidly expanding urban areas due to the loss and degradation of green and blue spaces with their regulating ecosystem services. The potential of nature-based solutions (NBS) to mitigate hydro-meteorological risks such as floods is increasingly recognized in Europe. However, its application in urban areas of SSA still needs to be systematically explored to inform and promote its uptake in this region. We conducted a multidisciplinary systematic review following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) protocol to establish the general patterns in the literature on NBS and hydro-meteorological risk mitigation in SSA. We searched scientific journal databases, websites of 12 key institutions and 11 NBS databases and identified 45 papers for analysis. We found at least one reported NBS in 71 % of urban areas of SSA across 83 locations. 62 % of the papers were clustered in South Africa, Kenya, Tanzania and Nigeria only, while the most studied cities were Dar es Salaam and Kampala. Moreover, 66 NBS practices were identified, most of which (n=44) were for flood mitigation. With only Mozambique (n=2) reporting NBS among the most at-risk countries, we found that NBS are implemented where risks occur but not where they are most severe. Mangrove restoration and wetland restoration, reforestation and urban forests, and agroforestry and conservation agriculture were the most common NBS practices identified for floods, extreme heat and drought mitigation, respectively. Traditional practices that fit the definition of NBS, such as grass strips and stone bunds, and practices more popular in the Global North, such as green roofs and green façades, were also identified. These NBS also provided ecosystem services, including 15 regulatory, 5 provisioning and 4 cultural ecosystem services, while 4 out of every 5 NBS created livelihood opportunities. We conclude that reported uptake of NBS for hydro-meteorological risks in SSA is low. However, there could be more NBS, especially at the local level, that are unreported. Furthermore, NBS can help SSA address major development challenges such as water and food insecurity and unemployment and help the sub-region develop climate-resiliently. We, therefore, recommend that NBS be mainstreamed into urban planning and for knowledge exchange opportunities between SSA and Europe and other regions to be explored to promote uptake.

Sub-Saharan Africa (SSA) is the region most vulnerable to climate change and related hydro-meteorological risks. These risks are exacerbated in rapidly expanding urban areas due to the loss and degradation of green and blue spaces with their regulating ecosystem services. The potential of nature-based solutions (NBS) to mitigate hydro-meteorological risks such as floods is increasingly recognized in Europe. However, its application in urban areas of SSA still needs to be systematically explored to inform and promote its uptake in this region. We conducted a multidisciplinary systematic review following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) protocol to establish the general patterns in the literature on NBS and hydro-meteorological risk mitigation in SSA. We searched scientific journal databases, websites of 12 key institutions and 11 NBS databases and identified 45 papers for analysis. We found at least one reported NBS in 71 % of urban areas of SSA across 83 locations. 62 % of the papers were clustered in South Africa, Kenya, Tanzania and Nigeria only, while the most studied cities were Dar es Salaam and Kampala. Moreover, 66 NBS practices were identified, most of which (n=44) were for flood mitigation. With only Mozambique (n=2) reporting NBS among the most at-risk countries, we found that NBS are implemented where risks occur but not where they are most severe. Mangrove restoration and wetland restoration, reforestation and urban forests, and agroforestry and conservation agriculture were the most common NBS practices identified for floods, extreme heat and drought mitigation, respectively. Traditional practices that fit the definition of NBS, such as grass strips and stone bunds, and practices more popular in the Global North, such as green roofs and green façades, were also identified. These NBS also provided ecosystem services, including 15 regulatory, 5 provisioning and 4 cultural ecosystem services, while 4 out of every 5 NBS created livelihood opportunities. We conclude that reported uptake of NBS for hydro-meteorological risks in SSA is low. However, there could be more NBS, especially at the local level, that are unreported. Furthermore, NBS can help SSA address major development challenges such as water and food insecurity and unemployment and help the sub-region develop climate-resiliently. We, therefore, recommend that NBS be mainstreamed into urban planning and for knowledge exchange opportunities between SSA and Europe and other regions to be explored to promote uptake.

Sub-Saharan Africa (SSA) is the region most vulnerable to climate change and related hydro-meteorological risks. These risks are exacerbated in rapidly expanding urban areas due to the loss and degradation of green and blue spaces with their regulating ecosystem services. The potential of nature-based solutions (NBS) to mitigate hydro-meteorological risks such as floods is increasingly recognized in Europe. However, its application in urban areas of SSA still needs to be systematically explored to inform and promote its uptake in this region. We conducted a multidisciplinary systematic review following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) protocol to establish the general patterns in the literature on NBS and hydro-meteorological risk mitigation in SSA. We searched scientific journal databases, websites of 12 key institutions and 11 NBS databases and identified 45 papers for analysis. We found at least one reported NBS in 71 % of urban areas of SSA across 83 locations. 62 % of the papers were clustered in South Africa, Kenya, Tanzania and Nigeria only, while the most studied cities were Dar es Salaam and Kampala. Moreover, 66 NBS practices were identified, most of which (n=44) were for flood mitigation. With only Mozambique (n=2) reporting NBS among the most at-risk countries, we found that NBS are implemented where risks occur but not where they are most severe. Mangrove restoration and wetland restoration, reforestation and urban forests, and agroforestry and conservation agriculture were the most common NBS practices identified for floods, extreme heat and drought mitigation, respectively. Traditional practices that fit the definition of NBS, such as grass strips and stone bunds, and practices more popular in the Global North, such as green roofs and green façades, were also identified. These NBS also provided ecosystem services, including 15 regulatory, 5 provisioning and 4 cultural ecosystem services, while 4 out of every 5 NBS created livelihood opportunities. We conclude that reported uptake of NBS for hydro-meteorological risks in SSA is low. However, there could be more NBS, especially at the local level, that are unreported. Furthermore, NBS can help SSA address major development challenges such as water and food insecurity and unemployment and help the sub-region develop climate-resiliently. We, therefore, recommend that NBS be mainstreamed into urban planning and for knowledge exchange opportunities between SSA and Europe and other regions to be explored to promote uptake.

There are many types of Nature-Based Solutions (NBS), such as intensive/extensive green roofs, green walls, retention ponds, Bioretention cells, treatment wetlands, river restoration, urban parks, and infiltration trenches. Each could contribute to one or more sustainable development goals as some can improve the ecosystem, some improve water resources, or mitigate urban flooding. Implementing the most suitable NBS in each area needs multidisciplinary perspective analysis by considering circular economy principles and the available resources that exhibit the importance of ranking the possible NBS that could be geo-based. Therefore, the main purpose of this study is to develop a novel ranking method for selecting the best NBSs in each area, which depends on plenty of geo-based variables such as climate type, water resource, economy, environment, Sustainable Development Goals (SDGs) and so forth. The developed dynamic geo-based ranking method has been validated through case-based assessment in different regions, confirming the proposed method’s effectiveness. In conclusion, the developed method could rank the selected NBS in each location, and according to geo-based information, it could show the implementation of the most suitable NBS, thus improving their role in the circular city.

<p>Nature-based solutions (NbS) are increasingly recognized as sustainable approaches to address socio-environmental challenges. Disaster risk reduction (DRR) has benefited by increasingly moving away from purely ‘grey’ infrastructure measures towards NbS, which can better provide cultural, aesthetic, and recreational co-benefits that are highly valued among European citizens. Public acceptance is of particular importance for NbS since they often rely on collaborative implementation, management, and monitoring, as well as protection against competing land uses. Although public engagement is a common goal of NbS projects and found in the IUCN’s core principles of NbS, outreach efforts are rarely based on a sufficient understanding of the (de)motivating factors tied to public perceptions. As a first step, we conducted a systematic literature review to examine how unique NbS characteristics relate to public acceptance through a comparison with grey measures. We identified influential acceptance factors related to individuals, society, and DRR measures. Based on the review, we introduce the PA-NbS framework as a starting point for the systematic consideration, design, and testing of strategies for increasing public acceptance. The PA-NbS highlights the roles of trust, competing interests, and effectiveness of NbS, as well as public perceptions of risk, nature and place.</p><p>A lack of consideration of these factors may lead to misaligned public expectations and failed participatory initiatives, while jeopardizing the success of NbS projects. Therefore, as a second step, we conducted citizen surveys within three NbS host communities. Distinct NbS being implemented within the OPERANDUM project aim to reduce risk from (socio-)natural hazards in Scotland (landslides and coastal erosion), Finland (eutrophication and algal blooms) and Greece (river flooding). Associations of factors related to risk, nature, and place perceptions with pro-NbS attitudes and behavior were tested to determine how these may be leveraged to increase acceptance. We find that trust is a consistent factor for defining attitudes towards the NbS across the sites. Attitudes are strongly associated with respondents’ commitment to nature and concern for risk, while some skepticism of NbS effectiveness leads to high public demand for relevant evidence. Risk perception and particularly the potential for future impacts are associated with behavioural acceptance (i.e. willingness to engage), along with responsibility for nature and connectedness to place.</p><p>Current data collection efforts to demonstrate NbS effectiveness for risk reduction are well-positioned to increase public acceptance in Europe. However, recognizing the differences among segments of the public within each site along with distinct hazard types, proposed NbS, and historical, social, and cultural characteristics across the sites is crucial for designing strategies that increase acceptance. An overview of these dynamics leads to evidence-based recommendations for the case-study sites and for successful NbS in Europe.</p>

Abstract. Sub-Saharan Africa (SSA) is the region most vulnerable to climate change and related hydro-meteorological risks. These risks are exacerbated in rapidly expanding urban areas due to the loss and degradation of green and blue spaces with their regulating ecosystem services. The potential of nature-based solutions (NBSs) to mitigate hydro-meteorological risks such as floods is increasingly recognised in Europe. However, its application in urban areas of SSA still needs to be systematically explored to inform and promote its uptake in this region. We conducted a multidisciplinary systematic review following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) protocol to establish the general patterns in the literature on NBSs and hydro-meteorological risk mitigation in SSA. We searched scientific journal databases, websites of 12 key institutions and 11 NBS databases and identified 45 papers for analysis. We found at least 1 reported NBS in 71 % of urban areas of SSA across 83 locations. Of the papers, 62 % were clustered in South Africa, Kenya, Tanzania and Nigeria only, while the most studied cities were Dar es Salaam and Kampala. Moreover, 66 NBS practices were identified, most of which (n=44) were for flood mitigation. With only Mozambique (n=2) among the most at-risk countries reporting NBSs, we found that NBSs are implemented where risks occur but not where they are most severe. Mangrove restoration (n=10) and wetland restoration (n=7), reforestation (n=10) and urban forests (n=8), and agroforestry (n=3) and conservation agriculture (n=2) were the most common NBS practices identified for floods, extreme-heat and drought mitigation, respectively. Traditional practices that fit the definition of NBSs, such as grass strips and stone bunds, and practices that are more popular in the Global North, such as green roofs and green façades, were also identified. These NBSs also provided ecosystem services, including 15 regulatory, 5 provisioning and 4 cultural ecosystem services, while 4 out of every 5 NBSs created livelihood opportunities. We conclude that the reported uptake of NBSs for hydro-meteorological risks in SSA is low. However, there could be more NBSs, especially at the local level, that are unreported. NBSs can help SSA address major development challenges such as water and food insecurity and unemployment and help the sub-region progress towards climate-resilient development. Therefore, we recommend that NBSs be mainstreamed into urban planning and knowledge exchange opportunities between SSA and Europe and that other regions be explored to promote uptake.

The use of nature-based solutions (NbS) to address the risks posed by hydro-meteorological hazards have not yet become part of the mainstream policy response, and one of the main reasons cited for this, is the lack of evidence that they can effectively reduce disaster risk. This paper addresses this issue, by providing model-based evidence from five European case studies which demonstrate the effectiveness of five different NbS in reducing the magnitude of the hazard and thus risk, in present-day and possible future climates. In OAL-Austria, the hazard is a deep-seated landslide, and the NbS analysed is afforestation. Modelling results show that in today's climate and a landcover scenario of mature forest, a reduction in landslide velocity of 27.6 % could be achieved. In OAL-Germany, the hazard is river flooding and the NbS analysed is managed grazing with removal of woody vegetation. Modelling results show that the NbS could potentially reduce maximum flood water depth in the near-future (2031–2060) and far-future (2070–2099), by 0.036 m and 0.155 m, respectively. In OAL-Greece, the hazard is river flooding, and the NbS is upscaled natural storage reservoirs. Modelling results show that in a possible future climate the upscaled NbS show most potential in reducing the total flooded area by up to 1.26 km2. In OAL-Ireland, the hazard is surface and river flooding, and the NbS is green roofs. Results from a modelled upscaling analysis under two different climate scenarios show that both maximum flood water depth, and total flooded area were able to be reduced. In OAL-UK, the hazard is shallow landslides, and the NbS is high-density planting of two different tree species. Modelling results under two different climate scenarios show that both tree species were able to improve slope stability, and that this increased over time as the NbS matured. The significance of these results is discussed within the context of the performance of the NbS over time, to different magnitude events, impact with stakeholders in engendering wider support for the adoption of the NbS in the OALs, and the uncertainty in the modelling analyses.

South Asian countries are highly susceptible to different forms of hydro-meteorological extremes (HMEs) like cyclones, storm surges, floods, erosion, sea level rise, etc., while changing patterns of climate variability also make the situations worse. Nature-based Solutions (NbS) in different forms, like mangrove forests, coral reefs, salt marshes, beach nourishment, reforestation and afforestation, wetland restoration, etc., can help to reduce the magnitude of impacts. This study was conducted in South Asia countries to understand the existing practices, challenges, and potentiality of NbS regarding HMEs. The findings of sea level rise-induced extreme events are summarized as follows: (a) Significance of coastal ecosystems in mitigating impacts of HMEs, (b) NbS approaches for coastal protection and restoration, (c) Co-benefits of NbS for coastal protection and restoration, (d) Coastal Protection and NbS: South Asia Perspective- (i) Current practices of NbS to protect the coastal region, (ii) Challenges to ensure NbS regarding coastal protection, and (iii) Potentiality of NbS to protect the coastal region.Unusual rainfall patterns and their connection to landslides, along with the environmental and socioeconomic consequences and threats to vulnerable groups, are examined. We also delve into NbS interventions that stabilize slopes and prevent erosion-related events, emphasizing the significance of early warning systems, community-based strategies, and disaster preparedness measures to enhance resistance and resilience. Case studies from Chittagong Hill Tracts and Rohingya Camps in Bangladesh demonstrate the customization of NbS approaches to meet particular needs.An in-depth analysis of diverse NbS approaches, including forest and floodplain restoration, construction of wetlands and green infrastructure, and several other solutions for urban flood prevention, is presented. The extent of their effectiveness and barriers to expanding NbS practices are discussed, encompassing a range of contexts from high-income urban areas to medium and low-income regions. The focus lies on the adaptability and potential impact of NbS in various contexts, providing valuable insights into their applicability. Barriers to large-scale implementation of NbS for urban flood prevention are elucidated, encompassing legislative, financial, and societal challenges that impede the integration of NbS in practice and policies, which hinder employing initiatives for a long-term national plan for NbS. Strategies to surmount these barriers are discussed, offering insights for stakeholders seeking to navigate the complexities of NbS integration. We conclude that although NbS can be considered a cost-effective and sustainable way to protect natural ecosystems and human properties, it needs more concentration to integrate into decision-making aspects from policy to practice perspectives.

Urbanization causes modifications in the urban climate of a city due to increase in impervious fraction and lack of evapotranspiration. The rise of extreme heatwave events due to climate change is causing concern for the cities effected by the urban heat island. Europe Union has recommended using Nature based solutions as a solution for multiple urban issues including the mitigation of urban heat. The UPSURGE project aims to use nature-based solutions for regenerative development in five demonstration cities. The five cities are based in different climate zones, consists of single to multiple demonstration sites, and are deploying various Nature based solutions based on the key city challenges.  The cities include Belfast, Breda, Budapest, Maribor, and Katowice. The demonstration sites are being Co-designed with multiple stakeholders to address the local concerns, diversity of voices to encompass perspectives and include citizens to address the longevity of Nature based solutions. The static and mobile sensors are being deployed to build a baseline and measure the effect of Nature based solutions. The cities have selected Nature based solutions varying from green roof, green wall, raingardens, Miyawaki forest, agroecology community gardens, rewilded zones, climate arboretum, meadows, water gardens. The work aims to model the effect of different Nature based solutions on the canopy urban heat island. The urban parameterization of the cities is done using local climate zone classification scheme. The advanced research Weather Research Forecast model is used to model the canopy urban heat island during the heatwave of July 2022. The WRF model is run for 7 days on three domains, 10 km, 5 km and 1 km horizontal resolution using six hourly data from ECMWF. The performance of the model has been assessed by analysing temperature, wind speed, relative humidity and surface level pressure considering their effect on local urban heat stress. The results showcase the importance of using actual urban morphology values in Weather Research Forecast to accurately simulate near-surface variables. The Weather Research Forecast simulations shows the presence of urban heat island and depicts the effect of deploying the various Nature based solutions across cities.

Assessing nature-based solutions for transformative change

Nature-based solutions play an essential role in enhancing urban soil hydrology by improving water retention properties, reducing surface runoff, and improving water infiltration. This bibliometric analysis study reviewed the literature and identified the current trends in research related to nature-based solutions in urban soil hydrology. The study has the potential to highlight current research areas and future hot topics in this specific field. The research used the Scopus database to collect published articles from 1973 to 2023. The keywords (“trees” OR “vegetation” OR “green infrastructure” OR “blue green infrastructure” OR “greenery” OR “nature-based solutions” AND “hydrolog*” AND “urban” OR “city” OR “soil”) were searched in the Scopus database, and 13,276 articles were retrieved. The obtained publications were analyzed for bibliometric analysis by using Bibliometrix (v4.3.0) and VOSviewer (v1.6.20) software. The maximum number of publications (970) related to nature-based solutions and urban soil hydrology was published in 2023. Additionally, countries such as the United States and China published 54.2% of articles of the global research in the field of nature-based solutions and urban soil hydrology, with 36% from the USA and 18.2% of articles from China. The bibliometric analysis depicted that Beijing Normal University led this specific research field with 540 articles. The top country in terms of collaboration was the USA, with 26.17% as compared to the global countries. The most productive researcher identified was Jackson, T.J., as he had the highest number of publications, showing his considerable contribution to the field. Furthermore, the most frequent keywords used in this research area were hydrology, ecosystem services, urban hydrology, remote sensing, nature-based solutions, climate change, runoff, stormwater management, water quality, vegetation, green roof, bioretention, and land use. The early research trending topics in this field from 2015 to 2023 were remote sensing, soil moisture, climate change, drought, green infrastructure, machine learning, and nature-based solutions. The bibliometric analysis identified limited interdisciplinary research integrations, not using well-significant and standardized methodologies for the evaluation of urban soil hydrology, and under-representation of research from developing countries as current research gaps. Future research directions highlight advanced methods such as combining data-driven technologies with traditional hydrological approaches, and increasing international collaboration, specifically in developing nations, to address urban soil hydrological problems properly.