Placemaking and Blue Green Infrastructure for Liveable, Resilient Places: Insights from Dundee, Scotland

<p>As global cities rethink their approaches to urban flood risk and water management in response to climate change, accelerating urbanisation and reductions in public green space, Blue-Green Infrastructure (BGI) is gaining increasing recognition due to the advantages of multifunctional BGI solutions over traditional piped drainage and grey infrastructure. BGI, including green and blue roofs, swales, rain gardens, street trees, ponds, urban wetlands, restored watercourses, reconnected floodplains, and re-naturalised rivers, is designed to turn ‘blue’ (or ‘bluer’) during rainfall events in order to reduce urban flood risk. In addition to managing flood risk and increasing water security, BGI generates a range of socio-cultural, economic and environmental co-benefits that help city authorities tackle other urban challenges and ultimately improve the quality of life of city dwellers.</p><p>Extensive research over the last decade has focused on improving knowledge of BGI systems in several broad areas, including: hydrological and hydraulic modelling of water flow through BGI assets; biochemical assessments of sediment and water quality; public preferences; identification and evaluation of BGI co-benefits, and; BGI planning and governance. Emerging research into adaptation pathways, natural capital accounting and social practice approaches for understanding community preferences demonstrate how BGI research is moving beyond hydrodynamic modelling to explore decision making under future uncertainty and placing greater emphasis on the role of community preferences in designing BGI that is accepted and supported by those who directly benefit.</p><p>This presentation will explore these emerging research areas, particularly focusing on the need for interdisciplinary research into BGI to enable the challenges and opportunities to be fully appreciated. Current knowledge gaps that present research opportunities in BGI will also be discussed, including the need for rigorous assessment criteria to determine the success of multifunctional BGI systems; greater investigation of the social benefits of BGI and the value people place on different types of BGI; the role of implicit perceptions in designing BGI assets, and; the role of urban watercourses as multifunctional BGI corridors able to safely convey stormwater while boosting water quality, providing multiple urban pathways (active transport, wildlife movements, etc.) and increasing green space in cities.</p>

Globally, cities are rethinking their approaches to urban flood risk and water management in response to the changing hydro-climate, accelerating urbanisation, reductions in public green spaces, and growing recognition of the advantages of multifunctional solutions over piped-drainage systems in tackling social, economic and environmental challenges. In this context, blue–green infrastructure, which comprises a wide range of assets including green and blue roofs, bioswales, rain gardens, restored watercourses and reconnected floodplains, is becoming established as a key component of urban flood resilience and water security planning and design. A Blue–Green City moves beyond the implementation of integrated treatment trains of blue–green and grey assets, towards the goal of creating a more natural urban hydro-cycle capable of generating multiple benefits that are valued by citizens and communities. In Blue–Green Cities these benefits are distributed in ways that are socially equitable, and blue–green+grey systems are maintainable in ways that are economically and environmentally sustainable. This chapter introduces the Blue–Green Cities concept and presents an overview of research undertaken by the Blue–Green Cities research project. The Blue–Green Cities research consortium envisaged and investigated novel flood risk management strategies that could be delivered as part of wider, integrated planning, designed to achieve urban renewal and environmental enhancement, and identify and rigorously evaluate the multiple benefits of blue–green infrastructure. The consortium was centred on ‘stakeholder and community communications’, and employed cutting-edge research methods in the engineering, environmental and social sciences to advance knowledge and understanding, while ensuring that the outcomes of the consortium (in terms of deliverables) exceeded the sum of its parts.

Managing flood risks in a changing climate

Blue-green infrastructure (BGI) has been recognized as an important tool for sustainable urban stormwater management. BGI is ecosystem-based, relying on biophysical processes, such as detention, storage, infiltration, and biological uptake of pollutants, to manage stormwater quantity and quality. Rain gardens, bioswales, constructed wetlands, retention and detention basins, and green roofs are most commonly used BGI systems. Unlike the single-functioned grey infrastructure, which is the conventional urban drainage system, these landscape systems collectively provide multiple ecosystem services, including flood risk mitigation, water quality treatment, thermal reduction, and urban biodiversity enhancement. In recent years, BGI is increasingly embraced through different initiatives around the world, driven by the urgency to tackle different local challenges, such as water quality standards, water security, increased flood risk, and aquatic ecosystem degradation. Whereas BGI is a relatively new term, the idea and practice are not new. In this chapter, we also showcase four cities—Portland , New York City, Singapore, and Zhenjiang—that are active and progressive in implementing BGI. Although BGI receives increasing attention, mainstreaming BGI remains a challenge today. To promote widespread BGI implementation, future research should focus on case studies on practical BGI experiences to inform strategies for overcoming the barriers to mainstreaming BGI in different cities.

In response to climate change and growing ecological threats, many cities are planning to increase the resilience of urban drainage systems, including the reduction of combined sewer overflows (CSOs) - one of the leading causes of surface water pollution. Blue green infrastructure (BGI) are growing in popularity to do so, and recent studies have made progress to evaluate the potential of BGI to eliminate CSOs. However, current research tends to consider a limited number of individual BGI elements and scenarios, often overlooking different combinations (e.g., bioretention basins combined with green roofs) and uncertainty in a future climate. The aim of this research is to evaluate the ability of a range of blue green infrastructure combinations to reduce CSOs under multiple future climate scenarios.A hydrological simulation model, EPA SWMM, is used to simulate the performance of a 95-hectare combined sewer system near Zurich, Switzerland. Four types of BGI are evaluated, including bioretention basins, porous pavements, green roofs, and stormwater ponds. The potential surface availability for each BGI element was quantified using GIS and LiDAR data, yet scenarios include a range of different implantation rates for each type. Combinations of BGI element types are generated by combining different implementation surfaces to the share of the BGI type (e.g., 20% of the available surface with the same share of bioretention basins, porous pavements and green roofs, etc.).Bioretention basins are assumed to be implemented on pervious surfaces (i.e., gardens, traffic islands), porous pavements on impervious surfaces (i.e., sidewalks, cycling lanes) and green roofs on flat roof buildings. Observed rainfall data (1990-2019) are used to simulated the baseline conditions, while more than five bias-corrected future rainfall timeseries (2070-2099) from EURO-CORDEX regional climate models (RCP 8.5) are used to represent a worst-case future climate. CSO Volume, duration and frequency are used to characterize system-wide CSO events across the seven outfalls.Preliminary results show that in a current climate, bioretention basins are most effective at reducing CSO volume, followed by porous pavements and green roofs. BGI do not relevantly reduce the duration and number of CSO events. In one future scenario, future precipitation is concentrated into shorter duration events, which consistently leads to shorter, higher intensity CSO events at a frequency similar to the historical record. Overall, the only scenario that can avoid an increase in future CSO volume is an extensive implementation of bioretention basins. Porous pavement and green roofs are less effective in a future climate because they can store limited amounts of water compared to bioretention basins. As rainfall intensities increase, the ability to retain large amounts of water will be the most effective. These results point to strategies with higher storage capacities to account for high-intensity rainfall events that are expected in the future. Future work will evaluate additional BGI elements, including urban ponds, and a more comprehensive set of BGI scenarios, future climate scenarios, and case studies, enabling a definition of guidelines and BGI design requirements at an urban scale for Switzerland.

Blue-green infrastructures (BGI) integrate solutions implemented to enhance water management and landscape values for more climateresilient and livable cities. BGI have created an opportunity to renew the natural structure of water balance in cities through the increase in rainwater retention and enlargement of permeable areas. The review of the literature on BGI development and solutions showed that the most popular BGI elements in terms of urban water quantity and quality were rain gardens, green roofs, vertical greening systems, and permeable pavements. Their structure and effectiveness were presented and reviewed. Despite the consensus between researchers that BGI benefit urban hydrology, differences in runoff decreased (2%-100%) lowering the peak flows (7%-70%) and infiltration (to 60%) or evapotranspiration (19%-84%) were reported. Due to an individual technical structure, each BGI element plays a specific role and there is no universal BGI solution against water-related problems. We inferred that the most effective ones were individually adapted solutions, which prevent from a stressor. The greater variety of solutions in a given area, the more benefits for the urban environment. Our analyses showed that a holistic and co-creative approach to create blue-green networks should be considered in modern water management plans.

Developing an adaptation option is challenging for long-term engineering decisions due to uncertain future climatic conditions; this is especially true for urban flood risk management. This study develops a real options approach to assess adaptation options in urban surface water flood risk management under climate change. This approach is demonstrated using a case study of Waterloo in London, UK, in which three Sustainable Drainage System (SuDS) measures for surface water flood management, i.e., green roof, bio-retention and permeable pavement, are assessed. A trinomial tree model is used to represent the change in rainfall intensity over future horizons (2050 s and 2080 s) with the climate change data from UK Climate Projections 2009. A two-dimensional Cellular Automata-based model CADDIES is used to simulate surface water flooding. The results from the case study indicate that the real options approach is more cost-effective than the fixed adaptation approach. The benefit of real options adaptations is found to be higher with an increasing cost of SuDS measures compared to fixed adaptation. This study provides new evidence on the benefits of real options analysis in urban surface water flood risk management given the uncertainty associated with climate change.

Flooding is the costliest natural disaster worldwide. In the UK flooding is listed as a major risk on the National Risk Register with surface water flooding the most likely cause of damage to properties. Climate change and increasing urbanisation are both projected to result in an increase in surface water flood events and their associated damages in the future. In this paper we present an Agent Based Model (ABM), applied to a London case study of surface water flood risk, designed to assess the interplay between different adaptation options; how risk reduction could be achieved by homeowners and government; and the role of flood insurance and the recently launched flood insurance pool, Flood Re, in the context of climate change. The ABM is novel in its coverage of different combinations of flood risk management options, insurance, and Flood Re, and its ability to model changing behaviour, decision making, surface water flood events, and surface water flood risk in a dynamic manner. The analysis highlights that while combined investment in property-level protection measures and sustainable urban drainage systems reduce surface water flood risk, benefits can be outweighed by continued development in high risk areas and the effects of climate change. Flood Re is beneficial in its function to provide affordable insurance, even under climate change, and is shown to have some positive effects on the housing market in the model. However, in our simulations Flood Re does face increasing pressure due to rising surface water flood risk, which highlights the importance of forward looking flood risk management interventions, that utilize insurance incentives, limit new development, and support resilience measures. Our findings are highly relevant for the ongoing regulatory and political approval process for Flood Re as well as the wider flood risk management discussion in the UK.

Green roofs—rooftops that are partially or completely covered with vegetation growing in soil medium over a waterproof membrane—have gained momentum over the past six years as building owners recognize their advantages over conventional roofing in terms of better energy efficiency and reduced rain runoff. Now local governments are exploring incentives for moving the practice into the mainstream. A look at cities that are leading the country in green roof coverage reveals a growing range of policy tools.

Urban blue-green infrastructures (BGIs) fulfill a variety of functions that enable cities to cope with climate change and additional urban anthropogenic pressures such as increasing population density, heat island effects, biodiversity loss, and progressive sealing of permeable surfaces. In the urban water cycle, BGIs can play an important role when it comes to both managing and mitigating the direct effects of ever-increasing periods of extended drought as well as the temporary excess of stormwater during and after heavy rainfall events. Although BGIs are multifunctional in principle, the individual infrastructure has to be designed and operated toward achieving a set of specific objectives, e.g., stormwater retention, infiltration, or storage for increased overall water resilience. In this study, we focus on green roofs as a key BGI for water resilient urban spaces. Green roofs have the advantage of unlocking underutilized roof space for urban water management and additional co-functions, avoiding additional urban land use conflicts at ground level. Green roofs are available in a multitude of design types based on the selection of vegetation, the make and thickness of the substrate layer, and the absence or presence of additional retention space. With GR2L, we present a robust dual-layer green roof water balance model that is able to cope with a variety of design aspects and was validated and calibrated using a data set of four green roof types with varying technical specifications and different vegetation cover. We used the calibrated models to assess how different green roof types operate under variable climatic conditions using meteo ensembles that consist of dry and wet years as well as a suite of randomly selected years. Calibration results indicate that a green roof factor (based on the classic crop factor) largely depending on the retention capacity of green roofs, makes the results widely applicable in planning. The results provide information on how green roof designs can be optimized for fulfilling a given set of water balance-driven multifunctionality objectives under varying climatic conditions and enabling an assessment of the performance of existing green roof designs against these conditions.

Due to their multifunctionality, blue-green infrastructure (BGI) such as bioretention cells and green roofs are increasingly adopted to manage stormwater and mitigate urban heat. Despite their multifunctional potential, current studies simulating BGI benefits tend to focus on a single objective, often overlooking how the proposed designs would perform across multiple functions. As a result, the heat mitigation potential of stormwater-focused BGI is not yet well understood.The goal of this study is to assess the impact that BGI primarily used for stormwater management, such as bioretention cells, porous pavements, and green roofs have on 2 m air temperature during the hottest hours of the day. To do so, we employ a microclimate model (Urban Tethys-Chloris, UT&C) to simulate over 20 BGI scenarios in three street canyon types—urban, residential, and industrial - in a town near Zurich, Switzerland. We also explore how properties affecting the stormwater management (e.g., variations in coverage, vegetation types, and soil properties) can alter canyon temperatures. Using measurements collected during the summer of 2024, the model was calibrated and validated (RMSE of 2.2°C and r2 of 0.84).Results show that BGI elements replacing impervious surfaces on the ground provide the greatest cooling effects (0.4 to 1°C of cooling). For example, bioretention cells replacing impervious surfaces achieved a temperature reduction of up to 1°C in urban street canyons. Porous pavements, though without vegetation, also contribute to cooling by allowing stormwater infiltration and direct evaporation, reducing temperatures by an average of 0.4°C. In contrast, replacing existing vegetation with bioretention cells slightly increased temperatures, likely due to soil properties that improve stormwater infiltration, resulting in drier topsoil layers and reduced evaporative cooling. Green roofs had negligible impact on 2m air temperature, likely because their cooling effect did not extend far enough to influence the street canyon. Sensitivity analysis demonstrated that dense vegetation, characterized by high albedo, a large leaf area index, and high evapotranspiration capacity, notably lowers temperatures compared to sparse vegetation with low albedo and limited evapotranspiration. Future work will assess how these results change under different scenarios, including with other types of BGI related to stormwater management, irrigation schemes, and in a future, more extreme climate. Overall, this work offers a deeper understanding of multifunctional BGI designs, highlighting potential trade-offs between stormwater management and heat reduction. By addressing these complexities, it supports a more holistic integration of BGI benefits in urban planning strategies.

Climate change is expected to affect the frequency, magnitude and seasonality of various precipitation-related hazards, including flooding as one of the costliest hazards in Europe. As natural hazards have a significant impact on infrastructure, human lives, and habitats, it is clear that adaptation measures aimed at both prevention and mitigation need to be considered to address climate change. Green (referred to as Nature-based) measures are currently being promoted by the European Union, but in some planning contexts these measures may not be fully capable of coping with predicted future climate hazards, especially in the case of extreme events. Furthermore, the implementation of such measures is often met with resistance from planning departments and decision makers due to institutional dependencies created by the use of grey infrastructure measures in the past. In addition, scepticism about the effectiveness of green measures goes hand in hand with a preference for grey measures. Hybrid measures do have a prevailing green visual look, they can fulfil some ecosystem services, but they require substantial technical equipment for implementation and may present a feasible complementary measure in planning context with limited space or already existing infrastructure. These solutions therefore combine parts of grey and green measures and present an alternative that can reflect the diversity of environmental conditions.This study evaluated the effectiveness of selected green (e.g. urban trees, rain gardens), grey (e.g. drywells, permeable sidewalks) and hybrid (e.g. green roofs, stormwater tree tranches) measures on flood risk using hydrological modelling with the HEC-HMS software. This study was carried out in order to define the most effective and suitable flood protection measures for the selected case study, the Glinšcica river basin in the municipality of Ljubljana in Slovenia. Based on the hydrological modelling performed, rain gardens were found to be the most effective measure in terms of reducing peak runoff and runoff volume for the Glinšcica river model. Both green roofs and stormwwater cisterns also showed relatively good results compared to the other measures. The hydrological study was combined with a public perception survey in which we investigated the acceptance, feasibility and effectiveness from the perspective of the Slovenian public. Therefore, we were interested in whether there are differences in the perception of the selected green, grey and hybrid flood risk management measures. We were also interested in which of the contextual (e.g., flood exposure and experience) and compositional (e.g., socio-demographics) factors influence public perception of the acceptability, feasibility, and effectiveness of these measures.Acknowledgment: The research was conducted within the project [Evaluation of hazard-mitigating hybrid infrastructure under climate change scenarios] co-granted by Slovenian Research Agency (J6-4628) and Czech Science Foundation (22-04520L). 

To overcome barriers to innovation in urban flood risk management and enable widespread implementation of blue–green infrastructure (BGI) to support cities in their transition towards Blue–Green City status, a range of biophysical, socio-political and governance uncertainties and challenges must first be identified, addressed and dealt with. In this chapter, an approach to identify and prioritise the barriers, or relevant dominant uncertainties (RDUs), that hamper blue–green decision-making is introduced and applied in two cities at different stages of BGI implementation: Portland, Oregon, USA, and Newcastle upon Tyne, UK. Strategies that have been employed to successfully overcome a range of barriers to innovative flood risk and stormwater management are presented and further discussed as part of three international and national best practice exemplars: the East Lents Floodplain Restoration Project, Portland, Oregon, USA; SuDS in Sutton’s Schools, London, UK; and Ellis Meadows BGI, Leicester, UK. These three examples demonstrate that identifying and managing the biophysical, socio-political and governance RDUs are essential for wider implementation of blue–green systems. This is because practitioners and policy-makers involved in delivering innovative flood risk and water management projects must have confidence that BGI components are scientifically sound, in addition to being supported, accepted and desired by the intended local beneficiaries.

Can Tho, the largest city in the Mekong River Delta, is experiencing rapid urbanisation that is causing many typical urbanisation-related issues, including the increasing flood risk. The flooding area has expanded from 30% to 50% of the total city area due to urbanisation and climate change. Due to the low topography and poor capacity of drainage systems, the city may sometimes remain inundated for up to three hours after the rain event has ended. It is essential to develop effective and also sustainable management strategies for the city to mitigate risk of flooding, especially surface water flooding caused by extreme heavy rainfall.Nature-based Solutions (NbS) are proposed and widely promoted globally as a sustainable strategy for managing flood risk and creating other benefits. For flood risk management, NbS can help a city reduce surface runoff and subsequently release pressure on drainage systems through infiltration and interception, thus mitigating flood risk. Numerical modelling has been widely used to support the design and assessment of NbS. Conventionally, NbS modelling is achieved by integrating a hydrological model with NbS simulation modules though a one-way coupling method. Such models are incapable of fully describing the rainfall-runoff-flooding processes dynamically interacting with NbS measures, and therefore can only provide limited information such as temporal and spatial variation of runoff removal rate for NbS design and evaluation.In this work, a 2D hydrodynamic flood model is adopted and further developed by coupling with compatible NbS simulation approaches to overcome the existing NbS restrictions. The new modelling framework is applied in Can Tho city to evaluate the feasibility and performance of different NbS against various evaluating metrics. The simulation results indicate that green roofs, rain gardens, and bio-retention cells can effectively reduce inundation area, flow rate, and runoff volume to protect localised infrastructure and key buildings under certain rainfall scenarios. However, dramatic change of flow velocities is observed near the key infrastructure and structures following the implementation of a rain garden, posing higher risk to pedestrians and vehicles. In-depth analysis of the hydrological performance of bio-retention cells further indicates that their designed capacity is not sufficiently exploited due to the inappropriate installation location, further demonstrating the advantage of the proposed model for better planning and design of NbS to achieve optimised performance.

Realizing a multifunctional blue-green infrastructure (BGI) as a nature-based solution for the urban water system and built environment within crowded city areas is seen as a promising route for the process of climate adaptation. BGI projects like rain gardens, green roofs, and water squares can be combined to achieve a variety of technical (drainage), environmental (biodiversity), economic (property development) and social (health and wellbeing) goals and values at a local neighborhood level. As integrating such values within local governments' existing fragmented structures and procedures has proved to be challenging, urban governments are increasingly experimenting with innovative governance approaches at different levels to capitalize on the multiple benefits of BGI. Nevertheless, policy actors who try to justify their choices in the face of value conflicts are both constrained and enabled by the institutions they can call on. Using a qualitative comparative case study, this article therefore aims to gain insight into different ways of, or approaches to, organizing value integration. In particular, we compare: (1) a top-down case of programmatic steering to translate value integration into a neighborhood approach; (2) a market-oriented innovative procurement approach to local public-private partnership projects; and (3) a case of invitational governance for a future-proof neighborhood that is striving for a sense of citizen ownership. Our findings demonstrate the conditions, drivers, and barriers to the value integration of different governance innovations in relation to time-related issues, the types of support available, organizational embedding, and stakeholder involvement. Our specific focus is on understanding how social and sustainability and spatial and technical values are integrated. This paper thus helps us to get to grips with different pathways to value integration in the context of urban infrastructures, as well as their applicability and the conditions for success. These insights will enable the further strengthening of our capacity to build climate-proof cities in a value-driven and integrative manner.