Ecological infrastructure refers to naturally functioning ecosystems that deliver valuable services to people, such as filtered water and disaster risk reduction. With natural resources becoming scarcer, there is a growing interest in reinvesting in naturally functioning ecosystems in the form of ecological infrastructure, with the assumption that ecological infrastructure complements engineered infrastructure. In many low- and middle-income countries, ecological infrastructure interventions are seen as a key strategy to simultaneously alleviate poverty and improve ecosystem functioning. However, the socio-economic outcomes of ecological infrastructure investments remain poorly documented. We address this knowledge gap by synthesizing research (n = 53 cases) that analyses how ecological infrastructure investments affect ten different socio-economic dimensions, such as income and food security in low- and middle-income countries. We find that ecological infrastructure investments primarily lead to positive outcomes for short-term income and natural capital, whereas positive outcomes for other socio-economic dimensions are less frequently observed. Cases with a high degree of participant involvement in the early implementation of ecological infrastructure investments are significantly more likely to capture positive outcomes across a variety of socio-economic dimensions. Analogously, cases spanning multiple methods – rather than adopting either a qualitative or a quantitative approach – report positive outcomes across more dimensions.
Habitat Type: URB
Urban environment
Nature-based solutions (NBS) can protect, manage and restore natural or modified ecosystems. They are a multidisciplinary, integrated approach to address societal challenges and some natural hazards effectively and adaptively, simultaneously providing human well-being and biodiversity benefits. NBS applications can be easily noticed in circular cities, establishing an urban system that is regenerative and accessible. This paper aims to offer a review on NBS for urban water management from the literature and some relevant projects running within the COST Action ‘Implementing nature-based solutions for creating a resourceful circular city’. The method used in the study is based on a detailed tracking of specific keywords in the literature using Google Scholar, ResearchGate, Academia.edu, ScienceDirect and Scopus. Based on this review, three main applications were identified: (i) flood and drought protection; (ii) the water-food-energy nexus; and (iii) water purification. The paper shows that NBS provide additional benefits, such as improving water quality, increasing biodiversity, obtaining social co-benefits, improving urban microclimate, and the reduction of energy consumption by improving indoor climate. The paper concludes that a systemic change to NBS should be given a higher priority and be preferred over conventional water infrastructure.
This article provides a perspective on nature-based solutions. First, the argument is developed that nature-based solutions integrate social and ecological systems. Then, theoretical considerations relating to relational values, multifunctionality, transdisciplinarity, and polycentric governance are briefly outlined. Finally, a conceptual model of the social–ecological system of nature-based solutions is synthesised and presented. This conceptual model comprehensively defines the social and ecological external and internal systems that make up nature-based solutions, and identifies theoretical considerations that need to be addressed at different stages of their planning and implementation The model bridges the normative gaps of existing nature-based solution frameworks and could be used for consistent, comprehensive, and transferable comparisons internationally. The theoretical considerations addressed in this article inform practitioners, policymakers, and researchers about the essential components of nature-based solutions. The conceptual model can facilitate the identification of social and ecological interconnections within nature-based solutions and the range of stakeholders and disciplines involved.
Policy monitoring and evaluation are important elements of the policy cycle, this help to initiate policy-makers to assess the proper implementation and adjust it as appropriate. This paper aims to evaluate the existing policy, strategies, and institutional arrangement on the development of urban green infrastructure in the three study areas; namely Hawassa, Wolayita Sodo, and Bodity town. Analyzing policy documents, key informant interview, and questionnaire survey were used to collect the required data. Descriptive statistics and policy analysis were also used to analyze the collected data from different sources. The study revealed that different strategies and standards were developed by the federal government, but it is not practically exercised at the regional and local level. The majority of government officials and experts agreed that existing policies and strategies related to UGI is not properly implemented. On the other hand, lack of policy and strategies are the major limitation in the development and management of UGI. Almost majority of the respondents confirmed that weak institutional arrangement has contributed to the poor implementation of UGI development. Lack of attention and awareness, the weak institutional arrangement is the main responsible factors for the absence of proper policy and poor implementation of strategies concerning UGI. Thus, actions needed for all the development of proper policies and strategies to improve UGI development.
Purpose: This paper aims to advance the idea of sustainable flood reduction. Flood reduction through the use of the drainage system is considered an unsustainable approach that decreases the use of water. In contrast, the Water Sensitive City is a sustainable concept aimed at increasing the value of water for human needs and reduce flooding. Design/methodology/approach: The current approach of relying on drainage systems is ineffective and must be combined with green infrastructures to reduce flooding. Green infrastructures can increase infiltration rates or facilitate rain harvesting. The study developed four scenarios that combine green and grey infrastructures and used the Soil and Water Assessment Tool (SWAT) model to select the most effective scenario based on the remaining amount of flood volume in every scenario. Findings: Green infrastructures that are related to increased infiltration and rain-harvesting instruments reduced flooding by 22.3 and 27.7 per cent, respectively. Furthermore, a combination of the two types of green infrastructures reduced flooding up to 45.5 per cent. Conversely, applying only grey infrastructures (by increasing drainage capacity) to reduce the flooding to zero is unfeasible, as this requires more than double the current capacity. Therefore, a combination of green and grey infrastructures can significantly reduce flooding in a water sensitive and feasible manner. Originality/value: Applying a combination of green and grey infrastructures is a new and effective approach to reduce flooding in the Kedurus Catchment Area.
Background: The increase in frequency and intensity of urban flooding is a global challenge. Flooding directly impacts residents of industrialized cities with aging combined sewer systems, as well as cities with less centralized infrastructure to manage stormwater, fecal sludge, and wastewater. Green infrastructure is growing in popularity as a sustainable strategy to mimic nature-based flood management. Although its technical performance has been extensively studied, little is known about the effects of green stormwater infrastructure on human health and social well-being. Methods: We conducted a multidisciplinary systematic review of peer-reviewed and gray literature on the effects of green infrastructure for stormwater and flood management on individuals’, households’, and communities’ a) physical health; b) mental health; c) economic well-being; and d) flood resilience and social acceptance of green infrastructure. We systematically searched databases such as PubMed, Web of Science, and Scopus; the first 300 results in Google Scholar; and websites of key organizations including the United States Environmental Protection Agency. Study quality and strength of evidence was assessed for included studies, and descriptive data were extracted for a narrative summary. Results: Out of 21,213 initial results, only 18 studies reported health or social well-being outcomes. Seven of these studies used primary data, and none allowed for causal inference. No studies connected green infrastructure for stormwater and flood management to mental or physical health outcomes. Thirteen studies were identified on economic outcomes, largely reporting a positive association between green infrastructure and property values. Five studies assessed changes in perceptions about green infrastructure, but with mixed results. Nearly half of all included studies were from Portland, Oregon. Conclusions: This global systematic review highlights the minimal evidence on human health and social well-being relating to green infrastructure for stormwater and flood management. To enable scale-up of this type of infrastructure to reduce flooding and improve ecological and human well-being, widespread acceptance of green infrastructure will be essential. Policymakers and planners need evidence on the full range of benefits from different contexts to enable financing and implementation of instfrastructure options, especially in highly urbanized, flood-prone settings around the world. Therefore, experts in social science, public health, and program evaluation must be integrated into interdisciplinary green infrastructure research to better relate infrastructure design to tangible human outcomes.
To guide investments in ecosystem-based adaptation (EbA) in developing countries, numerous stated preference valuation studies have been implemented to assess the value of ecosystem services. These studies increasingly use time payments as an alternative to money. There is limited knowledge, however, about how to convert time to money and how the type of payment affects willingness to pay (WTP). In this study, the results of choice experiments using time and money payments are compared in the context of EbA measures in Vietnam. Six, of which five individual-specific, conversion rates are applied. WTP estimates are found to be higher for time payments. Moreover, the type of payment vehicle as well as the conversion rate has substantial effect on mean WTP and WTP distributions. We discuss implications of these results for the conversion of time to money and the use of resulting WTP estimates in cost benefit analyses in developing countries.
Increasing human demands for ecosystem services due to climate change, population growth, poverty, lack of employment, tourism, and concomitant coastal property development threatens adaptive capacity in South Africa’s coastlines. Adaptation strategies frequently propose ecosystem-based adaptation (EBA) as a model for transformative change. However, several studies point to difficulties implementing EBA across the world. The aim of this paper is to assess to what extent social-ecological systems approaches and common pool resource (CPR) governance theories could inform EBA. Data obtained from interviews and surveys with policy makers and residents in South Africa’s Garden Route District were interpreted using the robustness framework (RF) and the design principles (DPs), two common tools for analyzing CPR governance. We found that the Garden Route coast is threatened by negative interactions between hard public and private infrastructures and ecological infrastructures (the cornerstone of EBA) which are driven by weak local government bodies and asymmetrical power relations. By coding the data for elements/interactions within the RF and then identifying and mapping the DPs onto the RF, we also revealed ways to leverage transformative EBA in the Garden Route. Our analyses suggest that the interactions between human-made and ecological infrastructures, as well as power relation, should be at the core of any development debate. Trade-offs should aim for maximum congruence between sustainability and equity in ecosystem services provisioning. This paper provides some considerations for researchers and decision makers to leverage transformative EBA that could potentially apply to areas experiencing similar challenges.
Nature-based adaptation planning is a challenging endeavor, not least because it requires transdisciplinary approaches to unite different actors’ efforts and capacities. However, empirical knowledge on associated governance processes is scarce and fragmented. Against this background, this paper examines the integration of nature-based approaches for climate change adaptation into municipalities’ daily planning practices and associated governance. A city-to-city learning lab was established to systematically analyze selected urban development projects step-by-step, from the initial idea, to comprehensive and detailed planning, procurement, implementation, maintenance and follow-up. The results show the numerous constraints municipal staff face and how they use targeted strategies to overcome them and tap into existing drivers. We identify five, complementary strategies: i) targeted stakeholder collaboration; ii) strategic citizen involvement; iii) outsourcing; iv) the alteration of internal working structures; and v) concealed science–policy integration. Importantly, these strategies reveal an increasing need for relational approaches that, in turn, require individuals to develop the cognitive/emotional capacity to establish trust, communicate inclusively and promote social learning, while at the same time dealing with an increasingly complex and uncertain working environment. We conclude that tapping into the potential of nature-based solutions for climate adaptation governance requires more financial and human resources, and capacity development to support personal development, systematic mainstreaming and, ultimately, more sustainable development.
Nature-based solutions (NBS) have recently received attention due to their potential ability to sustainably reduce hydro-meteorological risks, providing co-benefits for both ecosystems and affected people. Therefore, pioneering research has dedicated efforts to optimize the design of NBS, to evaluate their wider co-benefits and to understand promoting and/or hampering governance conditions for the uptake of NBS. In this article, we aim to complement this research by conducting a comprehensive literature review of factors shaping people’s perceptions of NBS as a means to reduce hydro-meteorological risks. Based on 102 studies, we identified six topics shaping the current discussion in this field of research: (1) valuation of the co-benefits (including those related to ecosystems and society); (2) evaluation of risk reduction efficacy; (3) stakeholder participation; (4) socio-economic and location-specific conditions; (5) environmental attitude, and (6) uncertainty. Our analysis reveals that concerned empirical insights are diverse and even contradictory, they vary in the depth of the insights generated and are often not comparable for a lack of a sound theoretical-methodological grounding. We, therefore, propose a conceptual model outlining avenues for future research by indicating potential inter-linkages between constructs underlying perceptions of NBS to hydro-meteorological risks
Hazards in coastal ecosystems, such as flooding and land loss, demand natural and nature-based solutions from local communities due to the protective and non-protective services they provide when compared with traditionally engineered approaches. In this context, natural solutions are those that consider conserving existing habitats whereas nature-based solutions are those created by humans. These solutions support important coastal ecosystem functions, such as nutrient uptake, fisheries habitat, soil carbon storage, and surge attenuation. Our main research questions were: (1) Based on community engagement, what are the possible natural and nature-based solutions to address coastal hazards in Breton Sound Estuary, Louisiana? and (2) How do these community co-designed nature-based solutions support various ecosystem functions? To help answer these questions, we leveraged the competency group methodology to incorporate the local needs and traditional ecological knowledge of community stakeholders into collaborative ecosystem modelling. In total, fifteen members regularly met five times over an eight-month period to design nature-based solutions to address coastal hazards. Two nature-based solutions, created marshes and restored ridges, were identified most frequently by the competency group (>75% occurrence) in a final survey. Associated ecosystem functions of the identified solutions were assessed with simulation models to determine future ecosystem functions of nutrient uptake, fisheries habitat, soil carbon storage, and surge attenuation after 20 years. By adding created marshes to an ecosystem, our model results indicate slight increases in nutrient uptake, likely increases to fisheries habitat and soil carbon storage capacity, as well as storm surge attenuation in some areas following ridge restoration. Quantifying these ecosystem functions with management actions has been limited and is needed to assess how natural and nature-based solutions impact local communities and resource users. This novel approach to modeling ecosystem-based solutions through a collaborative modeling process with researchers and residents can be applied elsewhere to assess the viability of natural and nature-based solutions.
Scholars and practitioners are increasingly promoting so-called nature-based approaches for urban climate change adaptation. There is widespread consensus that they both support and require transdisciplinary approaches, notably by involving citizens in the change process and finding innovative ways to unite different actors’ efforts and capacities. However, there is little empirical evidence regarding the actual value of citizen involvement to sustainability in this field. Against this background, this paper examines whether (or not) current forms and conditions of citizen involvement help to create a platform to support nature-based solutions and ensure a transformative adaptation process. The results show that under current conditions, citizen engagement often hampers sustainable outcomes. In fact, current structures and mechanisms for mainstreaming nature and climate considerations into sectoral planning are limited and, furthermore, neglect citizen involvement. In addition, there is a blind spot with respect to personal spheres of transformation toward sustainability regarding citizens, civil servants, and decision-makers. Key constraints are power structures and the lack of cognitive/ emotional and relational capacities required for improved democratic governance. If we are to tap into the potential of nature-based solutions to increase climate adaptation governance, we need targeted financial and human resources, and greater capacity to overcome current constraints and support all levels and phases of mainstreaming, notably planning, implementation, monitoring, and learning.
Cities face increasing environmental, social and economic challenges that together threaten the resilience of urban areas and the residents who live and work there. These challenges include chronic stresses and acute shocks, amplified by climate change impacts. Nature-based solutions have emerged as a concept for integrating ecosystem-based approaches to address a range of societal challenges. Nature-based solutions directly address and contribute to increased urban resilience. However, implementing nature-based solutions is inherently complex, given the range of ecosystem services, their multi-functionality and the trade-offs between functions, and across temporal and spatial scales. Urban planning can play a substantial role to support the implementation of nature-based solutions and to manage trade-offs and conflicts, as well as how social equity dimensions are considered. This paper presents a framework that guides the application of urban planning to nature-based solutions’ implementation, by addressing key trade-offs across temporal, spatial, functional and social equity aspects. The framework highlights the key questions, and the supporting information required to address these questions, to underpin the inclusion of nature-based solutions for urban resilience. We find that while urban planning can contribute substantially, there are continuing gaps in how the inherently anthropocentric urban planning processes can give voice to non-human nature.
Nature-based solutions attract more and more interest due to increasing maintenance costs of grey infrastructure, increasing design conditions and growing environmental awareness. Integrating ecosystems in coastal engineering practice not only scores with societal and ecological benefits, such as biodiversity and cultural services, but also provides coastal protection services by attenuating waves and stabilizing sediments. Although nature-based solutions can already be found along many coasts around the globe, coastal engineers are still posed to challenges when evaluating, designing, implementing or maintaining nature-based solutions as guidance and in-depth investigations on efficiency, vulnerabilities and natural dynamics are often lacking. Current challenges for science and practice relate to the general requirements of nature-based solutions, the determination of fundamental data and insecurities and knowledge gaps. To overcome these challenges, close collaboration of engineers and ecologists is necessary.
Climate change and urbanization have resulted in several societal challenges for urban areas. Nature-based solutions (NBS) have been positioned as solutions for enhancing urban resilience in the face of these challenges. However, the body of conceptual and practical knowledge regarding NBS remains fragmented. This study addresses this gap by means of a systematic review of the literature, to define NBS as a theoretical concept; its broader significance with respect to societal challenges; the key stakeholders in NBS planning, implementation and management; and major barriers to and enablers of NBS uptake. The results of this review reveal that, despite a lack of consensus about the definition of NBS, there is a shared understanding that the NBS concept encompasses human and ecological benefits beyond the core objective of ecosystem conservation, restoration or enhancement. Significant barriers to and enablers of NBS are discussed, along with a proposed strategic planning framework for successful uptake of NBS.
Nature-based solutions (NBS) in river landscapes, such as restoring floodplains, can not only decrease flood risks for downstream communities but also provide co-benefits in terms of habitat creation for numerous species and enhanced delivery of diverse ecosystem services. This paper aims to explore how landscape planning and governance research can contribute to the identification, design and implementation of NBS, using the example of water-related challenges in the landscape of the Lahn river in Germany. The objectives are (i) to introduce the NBS concept and to provide a concise definition for application in planning research, (ii) to explore how landscape planning and governance research might support a targeted use and implementation of NBS, and (iii) to propose an agenda for further research and practical experimentation. Our methods include a focused literature review and conceptual framework development. We define NBS as actions that alleviate a well-defined societal challenge (challenge-orientation), employ ecosystem processes of spatial, blue and green infrastructure networks (ecosystem processes utilization), and are embedded within viable governance or business models for implementation (practical viability). Our conceptual framework illustrates the functions of NBS in social-ecological landscape systems, and highlights the complementary contributions of landscape planning and governance research in developing and implementing NBS. Finally, a research and experimentation agenda is proposed, focusing on knowledge gaps in the effectiveness of NBS, useful approaches for informed co-design of NBS, and options for implementation. Insights from this paper can guide further studies and support testing of the NBS concept in practice
Coastal hazards pose a serious and increasing threat to the wellbeing of coastal communities. Adaptation responses to these hazards ideally need to be embedded in the local adaptation context. However, there is little understanding of factors that shape local adaptation choices, especially in rural and remote island settings. In this paper, we compile data on adaptation responses to coastal hazards and key factors that shape adaptation across 43 towns and villages in four Pacific island nations. Local communities cite erosion as a critical coastal hazard, even more often than coastal flooding and sea level rise. We find that communities prefer protective adaptation responses that use local knowledge and resources eand protect coastal ecosystems. Our findings reveal differences in preferred versus implemented adaptation responses.Ecosystem-based adaptation is the most commonly implemented response to coastal hazards. Seawalls and other hard structures are widely preferred and perceived as effective adaptation responses but are often not implemented due to a lack of social, institutional and technical capacity. Retreat is a highly unpopular adaptation response, and difficult to implement, as coastal communities in this study indicate a strong place attachment and are deeply embedded in their social and natural environment. Our results suggest that the selection of adaptation responses might involve important trade-offs between multiple, potentially conflicting, local priorities, such as the preference for seawalls and the need to protect coastal ecosystems. Findings emphasize the importance of considering the local context when making adaptation choices and show that even when responding to the same hazard, adaptation responses can vary significantly depending on local priorities and capacities.
Cities are dependent on their upstream watersheds for storage and gradual release of water into river systems. These watersheds act as important flood mitigation infrastructure, providing an essential ecosystem service. In this paper we use metrics from the WaterWorld model to examine the flood management-relevant natural infrastructure of the upstream watersheds of selected global cities. These metrics enable the characterisation of different types, magnitudes and geographical distributions of potential natural flood storage. The storages are categorised as either green (forest canopy, wetland and soil) or blue (water body and floodplain) storages and the proportion of green to blue indicates how different city upstream basin contexts provide different types and levels of storage which may buffer flood risk. We apply the WaterWorld method for examining flood risk as the ratio of accumulated modelled annual runoff volume to accumulated available green and blue water storage capacity. The aim of these metrics is to highlight areas where there is more runoff than storage capacity and thus where the maintenance or restoration of further natural infrastructure (such as canopy cover, wetlands and soil) could aid in storing more water and thus better alleviate flood risks. Such information is needed by urban planners, city authorities and governments to help prepare cities for climate change impacts.
Urban nature has the potential to improve air and water quality, mitigate flooding, enhance physical and mental health, and promote social and cultural well-being. However, the value of urban ecosystem services remains highly uncertain, especially across the diverse social, ecological and technological contexts represented in cities around the world. We review and synthesize research on the contextual factors that moderate the value and equitable distribution of ten of the most commonly cited urban ecosystem services. Our work helps to identify strategies to more efficiently, effectively and equitably implement nature-based solutions.
Limiting climate warming to <2°C requires increased mitigation efforts, including land stewardship, whose potential in the United States is poorly understood. We quantified the potential of natural climate solutions (NCS)—21 conservation, restoration, and improved land management interventions on natural and agricultural lands—to increase carbon storage and avoid greenhouse gas emissions in the United States. We found a maximum potential of 1.2 (0.9 to 1.6) Pg CO2e year−1, the equivalent of 21% of current net annual emissions of the United States. At current carbon market prices (USD 10 per Mg CO2e), 299 Tg CO2e year−1 could be achieved. NCS would also provide air and water filtration, flood control, soil health, wildlife habitat, and climate resilience benefits.
Ecological infrastructure (EI) refers to ecosystems that deliver services to society, functioning as a nature-based equivalent of, or complement to, built infrastructure. EI is critical for socio-economic development, supporting a suite of development imperatives at local, national and international scales. This paper presents the myriad of ways that EI supports sustainable development, using South Africa and the South African National Development Plan as a case study, linking to the Sustainable Development Goals on a global level. We show the need for EI across numerous development and sustainability issues, including food security, water provision, and poverty alleviation. A strategic and multi-sectoral approach to EI investment is essential for allocating scarce public and private resources for achieving economic and social-ecological priorities. Opportunities to unlock investment in EI, both internationally and on the national level, are identified. This includes leveraging private sector investment into landscape management and integrating the costs of managing EI into public sectors that benefit directly from ecosystem services, such as the water sector and infrastructure development. Additionally, investing in EI also aligns well with international development and climate change funds. Investment in EI from a range of innovative sources supports global and national development, while complementing other development investments.
Globally, shoreline protection approaches are evolving towards the incorporation of natural and nature-based features (living shorelines henceforth) as a preferred alternative to shoreline armoring. Emerging research suggests that living shorelines may be a viable approach to conserving coastal habitats (marshes, beaches, shallows, seagrasses) along eroding shorelines. Living shorelines typically involve the use of coastal habitats, such as wetlands, that have a natural capacity to stabilize the shore, restore or conserve habitat, and maintain coastal processes. They provide stability while still being dynamic components of the ecosystem, but due to their dynamic nature, careful designs and some maintenance will be required if habitat conservation is a goal. Living shorelines may represent a singular opportunity for habitat conservation in urban and developing estuaries because of their value to society as a shoreline protection approach and resilience to sea level rise. However, enhanced public acceptance and coordination among regulatory and advisory authorities will be essential to expand their use. To fully understand their significance as habitat conservation strategies, systematic and standardized monitoring at both regional and national scales is vital to evaluate the evolution, persistence, and maximum achievable functionality (e.g., ecosystem service provision) of living shoreline habitats.
Climate change disproportionately impacts the world’s poorest countries. A recent World Bank report highlighted that over 100 million people are at risk of falling into extreme poverty as a result of climate change. There is currently a lack of information about how to simultaneously address climate change and poverty. Climate change challenges provide an opportunity for those impacted most to come up with new and innovative technologies and solutions. This article uses an example from Mozambique where local and international partners are working side-by-side, to show how developing countries can simultaneously address climate change and poverty reduction using an ecosystem-based adaptation approach. Using ecosystem-based adaptation, a technique that uses the natural environment to help societies adapt to climate change, developing countries can lead the way to improve climate adaptation globally. This paradigm shift would help developing countries become leaders in ecosystem-based adaptation and green infrastructure techniques and has implications for climate policy worldwide.
Ecosystem-based approaches for climate change adaptation are promoted at international, national, and local levels by both scholars and practitioners. However, local planning practices that support these approaches are scattered, and measures are neither systematically implemented nor comprehensively reviewed. Against this background, this paper advances the operationalization of ecosystem-based adaptation by improving our knowledge of how ecosystem-based approaches can be considered in local planning (operational governance level). We review current research on ecosystem services in urban areas and examine four Swedish coastal municipalities to identify the key characteristics of both implemented and planned measures that support ecosystem-based adaptation. The results show that many of the measures that have been implemented focus on biodiversity rather than climate change adaptation, which is an important factor in only around half of all measures. Furthermore, existing measures are limited in their focus regarding the ecological structures and the ecosystem services they support, and the hazards and risk factors they address. We conclude that a more comprehensive approach to sustainable ecosystem-based adaptation planning and its systematic mainstreaming is required. Our framework for the analysis of ecosystem-based adaptation measures proved to be useful in identifying how ecosystem-related matters are addressed in current practice and strategic planning, and in providing knowledge on how ecosystem-based adaptation can further be considered in urban planning practice. Such a systematic analysis framework can reveal the ecological structures, related ecosystem services, and risk-reducing approaches that are missing and why. This informs the discussion about why specific measures are not considered and provides pathways for alternate measures/designs, related operations, and policy processes at different scales that can foster sustainable adaptation and transformation in municipal governance and planning.
A core concept in stormwater green infrastructure (GI) design is whether a system will meet its rainfall-runoff volume capture goals within a period of time after a previous event. In GI design, it is necessary not to view storms as singular, isolated events, but rather as a series of events, some of which are occurring within short durations and are often termed back-to-back events. This paper demonstrates the statistical rarity of back-to-back rainfall events that impact GI performance and analyzes the expected impact on the design of several GI systems for the mid-Atlantic region. Twenty-four scenarios were evaluated for common design events (2.5, 3.8, and 8.1 cm), followed by a substantial subsequent event (50-100% of the original storm volume) that occurred within the period where it would be expected that the GI system would be recovering capacity (24, 48, 72, or 96 h interevent period). The results indicated that only four scenarios had an annual average occurrence greater than one time per year, and 9 of the 24 scenarios had less than 0.1 annual average occurrences. Simple, conservative models of a bioinfiltration rain garden and green roof demonstrated that system storage capacity is almost always restored by infiltration and evapotranspiration within the prescribed interevent drawdown period, thus back-to-back events are not a primary concern. This finding was further confirmed with field site evidence from three GI sites at Villanova University, which regularly captured more than the design rainfall volume and only infrequently had minimal discharges for rainfalls smaller than design. An exception to this finding was that a green roof with a drainage layer did not exceed its design capacity because the drainage layer conveyed stored water away from the GI system before evapotranspiration could contribute to volume removal. These results demonstrate that the likelihood of large back-to-back events is very low, as is the chance of the design runoff volume being exceeded. This paper provides evidence that the existing required drawdown period for GI design can be overly restrictive for a system to meet its volume control goals, which may inhibit optimal implementation. The findings support more appropriate design through the development of regionally specific required drawdown times based on storm event frequency.