Review article : Potential of nature-based solutions to mitigate hydro-meteorological risks in sub-Saharan Africa

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 71ĝ€¯% of urban areas of SSA across 83 locations. Of the papers, 62ĝ€¯% were clustered in South Africa, Kenya, Tanzania and Nigeria only, while the most studied cities were Dar es Salaam and Kampala. Moreover, 66ĝ€¯NBS practices were identified, most of which (nCombining double low line44) were for flood mitigation. With only Mozambique (nCombining double low line2) 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 (nCombining double low line10) and wetland restoration (nCombining double low line7), reforestation (nCombining double low line10) and urban forests (nCombining double low line8), and agroforestry (nCombining double low line3) and conservation agriculture (nCombining double low line2) 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

Governance models for nature-based solutions: Seventeen cases from Germany

Nature-based solutions (NBS) for mitigating climate change are gaining popularity. The number of NBS is increasing, but research gaps still exist at the governance level. The objectives of this paper are (i) to give an overview of the implemented NBS for flood risk management and mitigation in Germany, (ii) to identify governance models that are applied, and (iii) to explore the differences between these models. The results of a hierarchical clustering procedure and a qualitative analysis show that while no one-size-fits-all governance model exists, polycentricism is an important commonality between the projects. The study concludes by highlighting the need for further research on traditional governance model reconversion and paradigm changes. We expect the findings to identify what has worked in the past, as well as what is important for the implementation of NBS for flood risk management in future projects.Horizon 2020 Framework Programme http://dx.doi.org/10.13039/100010661Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347Horizon 2020 http://dx.doi.org/10.13039/501100007601Horizon 2020 ()Technische Universität München (1025)Peer Reviewe

Restoring Rivers and Floodplains for Habitat and Flood Risk Reduction: Experiences in Multi-Benefit Floodplain Management From California and Germany

Conventional flood control has emphasized structural measures such as levees, reservoirs, and engineered channels—measures that typically simplify river channels and cut them off from their floodplain, both with adverse environmental consequences. Structural measures tend to be rigid and not easily adapted to increased flooding regimes resulting from environmental change. Such actions also limit the natural hydrologic benefits of floodplains such as storing floodwaters, improving water quality, providing habitat for invertebrates and fish during periods of inundation, and supporting a multitude of cultural services. As these benefits are more widely recognized, policies are being adopted to encourage projects that reduce flood risks and restore floodplain ecosystems, while acknowledging the social-ecological context. The number of such projects, however, remains small. We assessed four multi-benefit floodplain projects (two in California, United States, and two in Germany) and characterized their drivers, history, and measures implemented. In both United States cases, the dominant driver behind the project was flood risk reduction, and ecosystem restoration followed, in one case inadvertently, in the other as a requirement to receive a subsidy for a flood risk reduction project. One German case was motivated by ecosystem restoration, but it was more widely accepted because it also offered flood management benefits. The fourth case was conceived in terms of balanced goals of flood risk reduction, ecosystem restoration, and recreation. We conclude that projects that both reduce flood risk and restore ecosystems are clearly possible and often cost-effective, and that they could be more widely implemented. The principal barriers are often institutional and regulatory, rather than technical

Stakeholder Mapping to Co-Create Nature-Based Solutions: Who Is on Board?

Nature-based solutions (NBS) are inspired and supported by nature but designed by humans. Historically, governmental stakeholders have aimed to control nature using a top-down approach; more recently, environmental governance has shifted to collaborative planning. Polycentric governance and co-creation procedures, which include a large spectrum of stakeholders, are assumed to be more effective in the management of public goods than traditional approaches. In this context, NBS projects should benefit from strong collaborative governance models, and the European Union is facilitating and encouraging such models. While some theoretical approaches exist, setting-up the NBS co-creation process (namely co-design and co-implementation) currently relies mostly on self-organized stakeholders rather than on strategic decisions. As such, systematic methods to identify relevant stakeholders seem to be crucial to enable higher planning efficiency, reduce bottlenecks and time needed for planning, designing, and implementing NBS. In this context, this contribution is based on the analysis of 16 NBS and 359 stakeholders. Real-life constellations are compared to theoretical typologies, and a systematic stakeholder mapping method to support co-creation is presented. Rather than making one-fit-all statements about the “right” stakeholders, the contribution provides insights for those “in charge” to strategically consider who might be involved at each stage of the NBS project

Restauration des rivières urbaines : un concept socio-écologique

Les rivières sont un réservoir biologique et source de développement pour les sociétés humaines. À cause de l’étroite relation entre les Hommes et les écosystèmes fluviaux, elles furent identifiées comme un système socio-écologique. Hors, il s’effondre suite à l’exploitation intensive des services écosystémiques, à l’urbanisation croissante, et à la gestion de la ressource en eau priorisant la protection des biens, des usages et des personnes aux formes et fonctions des écosystèmes. Ces cinquante dernières années furent marquées par de nombreuses actions de restauration réalisées pour rétablir la qualité écologique et sociale des rivières. En Europe, la Directive Cadre sur l’Eau ratifiée en 2000 organise l’effort européen de restauration et demande l’atteinte du bon état ou potentiel écologique de toutes les masses d’eau des pays membres. Les rivières urbaines sont fortement affectées par l’impact anthropique mais leur restauration est particulièrement difficile. Alors que la science de la restauration évolue par les expériences passées, peu de connaissance existent sur les pratiques urbaines. Cette étude a pour objectif (1) d’identifier les différentes pratiques de la restauration et leurs forces motrices en mettant en avant les particularités des restaurations en milieu urbain. Et (2) d’évaluer les conflits au sein du système socio-écologique, notamment entre protection environnementale et usage récréatif et productif.Rivers are hotspots for biological diversity and sources of ecosystem services. Because of the close interactions between riverine ecosystems and human activities, rivers are recognized as a socio-ecological system. Centuries of intensive exploitation of the ecosystem services, urbanization, and water management focusing on the use of water and safeguarding humans from floods and diseases, rather than on ecological health, have led to severe degradations and functional losses. In recent years, restoration has been recognized as essential to reestablish the quality of the rivers and an increasing number of restoration projects have been implemented. In Europe, the Water Framework Directive orchestrates restoration efforts, and demands that all water bodies achieve their good ecological status or potential. In urban areas, most rivers are heavily impacted by human activities and social demand for restoration is high. However, little knowledge exists about urban restoration practices. This research aims (1) to identify the different restoration practices and drivers, and examine the particularities of urban river restorations, and (2) to assess the potential conflicts inside the socio-ecological system.Flüsse sind ein Hotspot für biologische Artenvielfalt und Erbringer vieler Ökosystemleistungen. Aufgrund der engen Wechselbeziehungen zwischen Flussökosystemen und menschlichen Aktivitäten werden sie als sozio-ökologische Systeme verstanden. Jahrhunderte massiven Nutzungsdrucks, Urbanisierung und eine Gewässerbewirtschaftung, die sich viel mehr der Versorgung der Menschen und dem Schutz derer vor Überschwemmungen und Krankheiten anstatt der Wahrung des ökologischen Gleichgewichts verschrieben hat, haben zu starken Zerstörungen und Funktionsverlusten dieser Ökosysteme geführt. In jüngster Zeit wurde die Notwendigkeit der Renaturierung von Flüssen zur Wiederherstellung ihrer Qualität erkannt und eine wachsende Zahl an Renaturierungsprojekten wurde realisiert. In Europa koordiniert die Wasserrahmenrichtlinie (Water Framework Directive, WFD) entsprechende Bemühungen und verlangt, dass alle Gewässer eine guten ökologischen Zustand oder ein gutes ökologisches Potenzial erreichen. In städtischen Gebieten sind die meisten Flüsse stark durch menschliche Aktivitäten geprägt und der Bedarf nach Renaturierungsmaßnahmen hoch. Dennoch gibt es nur wenige Kenntnisse über die Praktiken von Flussrenaturierungen in Städten. Diese Studie hat sich zum Ziel gesetzt (1) unterschiedliche Renaturierungspraktiken und deren Triebkräfte zu identifizieren und die Besonderheiten städtischer Flussrenaturierungen zu untersuchen und (2) die potenziell möglichen Interessenskonflikte im sozio-ökologischen System zu bewerten.河流是生物多样性研究的热点和诸多生态系统服务的来源。由于河岸生态系统与人 类活动的密切相互作用，使得河流通常被认为是一种社会生态系统。几个世纪以来，生 态系统服务的集约利用、城市化和水资源管理主要关注于水资源的有效利用和保障人类 免受洪水和疾病的危害而往往忽视了生态健康，从而导致了严重的生态退化和功能的丧 失。近年来，河流修复被公认为重建河流质量的必要手段并且越来越多的修复项目开始 付诸实施。在欧洲，欧盟水框架指令对水资源的修复工作进行策划统筹，并对所有水体 需达到的生态状况或生态潜力提出了高的要求。在城市地区，绝大多数的河流深受人类 活动的影响并且对于河流修复的社会需求较高。然而，关于城市河流修复实践的相关知 识还非常缺乏。本研究旨在：（1）区分不同的河流修复实践项目及其驱动力，以及研究 城市河流修复的特殊性；（2）并对这一社会生态系统中存在的潜在冲突进行评估

La rivière et des hommes : quelle gouvernance pour la restauration des rivières ?

National audienceIn the context of increasing renewable energy need to tackle climate change driver, emerging wisdom regarding freshwater ecological protection, and increasing flood risk due to weather pattern changes, river management was never been that stretched between conflicting goals. To adapt to such environmental and societal changes, sustainable management strategies should be implemented. Their design rises crucial questions, as how the responsible use of the resource can be integrated into high efficient river management. This contribution synthesizes and presents the results of many pieces of research on sustainable river use and on the institutionalization of river restoration processes. This study goes beyond the theoretical approach and is based on the observation of cases already carried out, e.g., the restoration of the Isar in Munich (Germany). This contribution shows the complexity of restoration projects considering its various objectives, the constellation of the institutions concerned and the game of local actors. The discussion highlights the decisive drivers and mechanisms for resilient river management. More particularly, polycentric governance and participatory planning are identified as success factors.Dans le contexte de l'augmentation des besoins en énergie renouvelable pour lutter contre les moteurs du changement climatique, de l'émergence de la conscience écologique, de l'augmentation des risques d'inondation dus aux changements climatiques, et de la crise écologique, la gestion des rivières n'a jamais été aussi tendue entre des objectifs contradictoires. Pour s'adapter à ces changements environnementaux et sociétaux, des stratégies de gestion durable doivent être mises en œuvre. Quelle gouvernance de la rivière peut apporter les solutions au challenge du 21ème siècle ? Cette contribution synthétise et présente les résultats de nombreux travaux de recherche sur l’institutionnalisation de la restauration de rivière. Cette étude va au-delà de l'approche théorique et s'appuie sur l’observation de cas déjà réalisés tels que la restauration de l’Isar. Elle montre la complexité des projets de restauration considérant ses objectifs variés, la constellation des institutions concernées et le jeu des acteurs locaux. La discussion met en avant les moteurs et mécanismes décisifs pour une gestion résiliente de la rivière. Plus particulièrement la gouvernance polycentrique et la planification participative sont montrées comme facteurs de succès

Model-Based Evaluation of Urban River Restoration: Conflicts between Sensitive Fish Species and Recreational Users

Urban rivers are socioecological systems, and restored habitats may be attractive to both sensitive species and recreationists. Understanding the potential conflicts between ecological and recreational values is a critical issue for the development of a sustainable river-management plan. Habitat models are very promising tools for the ecological evaluation of river restoration projects that are already concluded, ongoing, or even to be planned. With our paper, we make a first attempt at integrating recreational user pressure into habitat modeling. The objective of this study was to analyze whether human impact is likely to hinder the re-establishment of a target species despite the successful restoration of physical habitat structures in the case of the restoration of the Isar River in Munich (Germany) and the target fish species Chondostroma nasus L. Our analysis combined high-resolution 2D hydrodynamic modeling with mapping of recreational pressure and used an expert-based procedure for modeling habitat suitability. The results are twofold: (1) the restored river contains suitable physical habitats for population conservation but has low suitability for recruitment; (2) densely used areas match highly suitable habitats for C. nasus. In the future, the integrated modeling procedure presented here may allow ecological refuge for sensitive target species to be included in the design of restoration and may help in the development of visitor-management plans to safeguard biodiversity and recreational ecosystem services

Societal Drivers of European Water Governance: A Comparison of Urban River Restoration Practices in France and Germany

The European water governance took a decisive turn with the formulation of the Water Framework Directive (WFD), which demands the restoration of all water bodies that did not achieve sufficient ecological status. Urban rivers are particularly impaired by human activities and their restorations are motivated by multiple ecological and societal drivers, such as requirements of laws and legislation, and citizen needs for a better quality of life. In this study we investigated the relative influence of socio-political and socio-cultural drivers on urban river restorations by comparing projects of different policy contexts and cultural norms to cross-fertilize knowledge. A database of 75 projects in French and German major cities was compiled to apply (a) a comparative statistical analysis of main project features, i.e., motivation, goals, measures, morphological status, and project date; and (b) a qualitative textual analysis on project descriptions and titles. The results showed that despite a powerful European directive, urban river restoration projects still keep national specificities. The WFD drives with more intensity German, rather than French, urban river restoration. This study showed the limits of macro-level governance and the influence of microlevel governance driven by societal aspects such as nature perception and relationships between humans and rivers

Nature-Based Solutions—Concept, Evaluation, and Governance

Climate change results in an increase of the frequency and intensity of extreme hydro-meteorological risks such as floods, mudflows, landslides, avalanches and rockfalls jeopardizing a great number of people, settlements and critical infrastructures every year [...

Non-Structural Flood Management in European Rural Mountain Areas—Are Scientists Supporting Implementation?

Mountain areas are highly exposed to flood risks. The latter are increasing in the context of climate change, urbanization, and land use changes. Non-structural approaches such as nature-based solutions can provide opportunities to reduce the risks of such natural hazards and provide further ecological, social, and economic benefits. However, few non-structural flood mitigation measures are implemented in rural mountain areas so far. The objective of this paper is to investigate if the scientific boundaries limit the implementation of non-structural flood management in rural mountain areas. In the study, we statistically analyzed the knowledge about flood management through a systematic literature review and expert surveys, with a focus on European rural mountain areas. Both methods showed that scientific knowledge is available for decision makers and that nature-based solutions are efficient, cost-effective, multifunctional, and have potential for large-scale implementation