Grey Infrastructure Research Articles

Greener or Greyer? Exploring the Trends of Sealed and Permeable Spaces Availability in Italian Built-Up Areas during the Last Three Decades

Increasing the availability of greenspaces in built-up areas (GSB) is one of the main challenges to improving sustainability and livability in urban landscapes. Concurrently, the availability of brownfields and permeable spaces offers the chance to increase sustainability through the implementation of Nature-Based Solutions. This work aims to evaluate how land use/cover changes influenced the availability of permeable spaces in Italian built-up areas over the last three decades. These spaces were classified according to population density, vegetation type, and average size, to better characterize recent dynamics (2008–2016) and offer remarks and tips concerning ongoing soil sealing dynamics. According to the findings, despite an overall increase of 41.5% in built-up areas with respect to their 1990 extension, permeable spaces increased only by 25.2% during the same time-span, moving from 49.8% coverage in 1990 to 44.7% today, in relation to the whole national built-up area. Moreover, our in-depth analysis for the 2008–2016 period shows that forested spaces increased by 0.4%, while permeable unforested ones decreased by 0.7%, especially in thinly and intermediately populated areas. Overall, the scarcity of these spaces should be carefully considered when assigning residual vacant lots to new buildings and grey infrastructure, especially in densely populated areas. The proposed methodology provides reliable estimates and represents a starting point to develop advanced monitoring tools supporting sustainable urban policies.

Tree Information Modeling: A Data Exchange Platform for Tree Design and Management

Trees integrated into buildings and dense urban settings have become a trend in recent years worldwide. Without a thoughtful design, conflicts between green and gray infrastructures can take place in two aspects: (1) tree crown compete with living space above ground; (2) built underground environment, the other way round, affect tree’s health and security. Although various data about urban trees are collected by different professions for multiple purposes, the communication between them is still limited by unmatched scales and formats. To address this, tree information modeling (TIM) is proposed in this study, aiming at a standardized tree description system in a high level of detail (LoD). It serves as a platform to exchange data and share knowledge about tree growth models. From the perspective of architects and landscape designers, urban trees provide ecosystem services (ESS) not only through their overall biomass, shading, and cooling. They are also related to various branching forms and crown density, forming new layers of urban living space. So, detailed stem, branch and even root geometry is the key to interacting with humans, building structures and other facilities. It is illustrated in this paper how these detailed data are collected to initialize a TIM model with the help of multiple tools, how the topological geometry of stem and branches in TIM is interpreted into an L-system (a common syntax to describe tree geometries), allowing implementation of widely established tree simulations from other professions. In a vision, a TIM-assisted design workflow is framed, where trees are regularly monitored and simulated under boundary conditions to approach target parameters by design proposals.

Multi-stage planning of LID-GREI urban drainage systems in response to land-use changes

Long-term planning of urban drainage systems aimed at maintaining the sustainability of urban hydrology remains challenging. In this study, an innovative multi-stage planning framework involving two adaptation pathways for optimizing hybrid low impact development and grey infrastructure (LID-GREI) layouts in opposing chronological orders was explored. The Forward Planning and Backward Planning are adaptation pathways to increase LID in chronological order based on the initial development stage of an urban built-up area and reduce LID in reverse chronological order based on the final development stage, respectively. Two resilience indicators, which considered potential risk scenarios of extreme storms and pipeline failures, were used to evaluate the performance of optimized layouts when land-use changed and evolved over time. Compared these two pathways, Forward Planning made the optimized layouts more economical and resilient in most risk scenarios when land-use changed, while the layouts optimized by Backward Planning showed higher resilience only in the initial stage. Furthermore, a decentralized scheme in Forward Planning was chosen as the optimal solution when taking costs, reliability, resilience, and land-use changes into an overall consideration. Nevertheless, this kind of reverse optimization order offers a novel exploration in planning pathways for discovering the alternative optimization schemes. More comprehensive solutions can be provided to decision-makers. The findings will shed a light on the exploration of optimized layouts in terms of spatial configuration and resilience performance in response to land-use changes. This framework can be used to support long-term investment and planning in urban drainage systems for sustainable stormwater management.

Global expansion of sustainable irrigation limited by water storage

Providing affordable and nutritious food to a growing and increasingly affluent global population requires multifaceted approaches to target supply and demand aspects. On the supply side, expanding irrigation is key to increase future food production, yet associated needs for storing water and implications of providing that water storage, remain unknown. Here, we quantify biophysical potentials for storage-fed sustainable irrigation-irrigation that neither depletes freshwater resources nor expands croplands but requires water to be stored before use-and study implications for food security and infrastructure. We find that water storage is crucial for future food systems because 460 km3/yr of sustainable blue water, enough to grow food for 1.15 billion people, can only be used for irrigation after storage. Even if all identified future dams were to contribute water to irrigation, water stored in dammed reservoirs could only supply 209 ± 50 km3/yr to irrigation and grow food for 631 ± 145 million people. In the face of this gap and the major socioecologic externalities from future dams, our results highlight limits of gray infrastructure for future irrigation and urge to increase irrigation efficiency, change to less water-intensive cropping systems, and deploy alternative storage solutions at scale.

Evaluation of urban infrastructure policies in Turkey for climate resilience and adaptation

ABSTRACT Turkey is a country vulnerable to the negative effects of climate change. In urban areas where most of the population lives, floods occur due to sudden, short-term but heavy rains caused by climate change. Infrastructure deficiencies have also caused considerable loss of life and property. I have discussed policies and practices of public administration formed by central government and local administrations focusing on climate change resilience and adaptation. I have also evaluated policy areas that need further development. This study can contribute to finding solutions to problems faced by cities in Turkey and other nearby countries. Findings show that participatory processes involving scientific and local knowledge can play a key role. Green and blue infrastructure with grey infrastructure and associated engineering solutions should also be used. Legislation should be updated to expand the use of nature-based solutions and green infrastructure, which should form a key focus of urban policy development.

Nature-based solutions (NbS) and climate change adaptation in Bangladesh: does planning law facilitate NbS for climate change adaptation in Dhaka?

ABSTRACT Flooding is exacerbated by climate change, and the ecosystem functions of wetlands can assist in mitigating risk and contribute to climate adaptation. Nature based solutions (NbS) have emerged as an alternative to the exclusive reliance on grey infrastructure to drive climate adaptation responses to flooding. This article critically examines the role of planning law to facilitate NbS in the urban context of Dhaka, Bangladesh. The article will explore the following research question: does land use planning law in Bangladesh help facilitate the establishment and maintenance of NbS to assist in adapting to climate flood risk? This article will assess existing planning law on its ability to integrate NbS into the urban climate adaptation context while managing competing and incompatible land use and upholding strong, transparent and equitable governance. This article finds that the inability to enforce regulations and a lack of early consultation and engagement presents serious impediments to implementing NbS through planning law and development policy in Dhaka and contributes to a disconnect between high level policy documents and implementation on the ground, thereby undermining climate change adaptation interventions.

Impact of climate change on coastal water quality and its interaction with pollution prevention efforts

The impact of climate change on nearshore coastal water quality and its interaction with pollution prevention efforts (e.g., the development of green and gray water infrastructure) still lack systematic investigation. This study performed a holistic analysis of the impact of climate change on the salinity and concentrations of total nitrogen (TN), total phosphorus (TP) and chlorophyll a (Chl.a) in Shenzhen Bay between Shenzhen and Hong Kong, the two most developed megacities in South China, based on three-dimensional hydrodynamic and water quality modeling. The major study findings were as follows. First, Chl.a was the most sensitive parameter, and its bay-wide average concentration in 2100 was predicted to be approximately 13% and 46% higher than those in 2015 under mild and rapid climate change scenarios, respectively. Second, sea level rise was found to be a major driver of all four water quality parameters, while temperature and radiation mainly influenced Chl.a and precipitation mainly influenced nutrients. Third, water quality responses to climate change were highly heterogeneous over the bay. Even under a mild climate change scenario, the highest location-specific changes (2100 vs. 2015) in salinity and TN, TP and Chl.a concentrations were projected to be approximately 21%, 19%, 25%, and 65%, respectively. Fourth, changes in seasonal variation due to climate change may lead to an enhanced ecological risk of algal blooms. Finally, the effect of reducing TN and TP concentrations by proposed water infrastructure development was found to be significantly weakened (nearly 40% and 20% for TN and TP, respectively, under a mild climate change scenario), while the negative effect (i.e., increase in the Chl.a concentration) was notably accelerated. Regional cooperation is critical for protecting the water quality of the bay, particularly under climate change. The insights obtained in this study are applicable to other coastal water zones around the world with similar socioeconomic backgrounds and climatic conditions.

Regulatory requirements and voluntary interventions create contrasting distributions of green stormwater infrastructure in Baltimore, Maryland

Green stormwater infrastructure (GSI) has been increasingly promoted as a strategy to augment gray infrastructure because it can reduce flooding, improve water quality, and provide additional social and ecological benefits. Government regulations in many places now require or encourage the use of GSI to mitigate impacts of development, while numerous funding opportunities incentivize installation of additional GSI features to enhance community and environmental benefits. The equity of GSI benefits may be affected by these different underlying motivations for GSI installation—mandatory compliance with regulations vs voluntary community improvement—which could create distinct patterns of GSI across the landscape. We examined this hypothesis in Baltimore, Maryland, USA, by comparing the city’s database of GSI facilities that meet regulatory requirements (“regulatory GSI”) to a dataset we compiled of GSI installed voluntarily by nonprofit organizations and community groups (“voluntary GSI”). We found that regulatory GSI included more facility types than voluntary GSI, which was dominated by microscale practices like rain gardens. The presence of regulatory GSI was negatively related to greater Black populations, while voluntary GSI was more likely to be found both in low-income areas with predominantly Black populations and in high-income areas with predominantly white populations. Voluntary GSI was much more commonly located on public land, and GSI on public land tended to be in more disadvantaged areas. These patterns of GSI distribution, which reflect different motivations and constraints in a fragmented implementation process, provide an opportunity for improving equitable access to GSI benefits through more systematic planning and management efforts.

Categorization of green and grey infrastructure complexity in the rural–urban interface of Bengaluru, India: an unsupervised volumetric approach with relevance for urban quality

Trees are key elements of urban green infrastructure and provide multiple ecosystem services that are essential for the quality of life of people in urban environments. Grey infrastructure is made up of buildings or built-up area, generally characterized by imperviousness of the surface. The complexity of urban green and grey infrastructure and their interactions co-define the quality of urban life and the ecological value of urban areas. Using conventional dichotomies by separation into “urban” and “rural” contexts does hardly allow to comprehensively assess the situation in rapidly urbanizing environments of the Global South. We present an unsupervised remote sensing-based approach that integrates 3D information to objectively categorize the complexity of green and grey infrastructure. Using the rural–urban interface of Bengaluru, India, as a case example, we distinguished five categories that describe the composition and configuration of green and grey infrastructure, where three variables served as indicators for categorization into five clusters. We argue that such integrated 3D assessment of green and grey infrastructure is particularly useful for understanding and classifying “rurban” environments, where a distinction between urban and rural is often no longer possible. Our final map allows to quantitatively characterize such rurban configurations.

Social inequality deeply affects people’s perception of ecosystem services and disservices provided by street trees

To ensure that changes in the landscape do not reinforce existing inequalities or create new ones, it is vital to continuously monitor the urban landscape. This is especially important in situations of poverty and economic and environmental inequality. However, little is known about the influence of socioeconomic factors on peoples’ perception of Ecosystem Services (ES) in Latin American cities, where a weak environmental governance, deep social inequality and high biodiversity and degree of endemism will differently determine the supply and demand of ESs. In this study, we investigated the social perception of a range of ESs and Ecosystem Disservices (i.e., negative impacts of ecosystems on people; ED) delivered by the street trees of Rio de Janeiro (Brazil), a city marked by a strong socioeconomic inequality. For this, we used a questionnaire investigating how the perceptions about the provision of ESs and EDs by street trees is modulated by sociodemographic (e.g., age and gender), urban (e.g., population density), socioeconomic (e.g., Social Development Index; SDI) and ecological factors (e.g., street trees density). For that, we used bi- and multi-variate analysis, including principal component analysis. We found that in neighborhoods with lower SDI, lower population density, lower species richness and higher arboreal deficit, respondents identified more ESs related to food provision, air quality, noise, and flood regulation while in neighborhoods with opposite characteristics, residents tend to affirm the esthetic identity of their neighborhoods, which are usually better maintained in terms of both green and grey infrastructures. Female respondents identified more safety EDs regarding negative aspects of street trees (e.g., risk of crime). Also, younger respondents identified for more regulatingservices (e.g., climate regulation and habitat support). We demonstrate that local assessment of ESs and EDs is necessary to adequately instruct suitable strategies for increase people's engagement, identify potential conflicts, as well as planning, designing, and managing the green infrastructures.

Realistic representation of city street-level human thermal stress via a new urban climate-human coupling system

Urban overheating aggravated by climate change and rapid urbanization poses a severe threat to thermal health of urban residents. To more realistically represent street-level heat stress, we propose a new urban climate-human coupling system by integrating an advanced urban canopy model (UCM) with a new human-environment adaptive thermal stress (HEATS) module. The coupled UCM-HEATS system features a state-of-the-art solution to complicated human-street radiative exchanges and incorporates dynamic human thermoregulatory responses to microclimatic changes. The UCM-HEATS system was evaluated in a typical hot and humid city, Hong Kong, and then applied to investigate street-level thermal stress in various urban settings and under different personal conditions. By explicitly resolving shading effects of buildings and trees on human radiation budgets, our study emphasizes the marked effectiveness of active shade management using green and gray infrastructure on daytime heat mitigation, proposing a “right shade, right place, right time” paradigm for regulating important street canyon geometries (building height, road width, and tree crown width) and orientations. Additionally, human evaporative heat dissipation can be hindered by urban moisture islands and wind impediments; thus, a detailed urban ventilation strategy is suggested considering different temperature-humidity combinations. For personal heat protection, we identified an evident cooling effect of high-albedo clothing and a thermal-comfort-optimal walking speed. Special attention is paid to heat-vulnerable groups, especially older people who suffer from notably higher heat risks during pandemics with facemask-induced heat burden. Bridging urban climate and human ergonomics, this study aims to advance human-centric urban design toward future smart, resilient, and inclusive cities.

Study on the land surface cover dynamics of built-up areas and its implication for sustainable urban planning in Hawassa city, Ethiopia

Rapid and uncontrolled urbanization is one of the drivers responsible for land cover Change dynamics in Ethiopia. In most of the cities and towns of Ethiopia, the proportion of different types of urban land surface cover and trends of change in each are unknown and thus hindering environmentally sustainable urban planning. This study describes different land surface cover types and their dynamics of change, and subsequent influence on the Land Surface Temperature of Hawassa city between 2011 and 2021. The i-Tree canopy and Landsat 5 (TM) and Landsat 8 (OLI) images were used for 2011 and 2021 to analyze the land surface cover and surface temperature change, respectively. The results show that bare soil is the dominant land surface cover type (23.4%), followed by tree canopy cover (21.4%), while impervious roads occupied the smallest land surface area cover (3.4%) along with water bodies (1%). In 10 years most of the land surface cover types increased positively, including tree covers by + 9.8%. The only exceptions were bare soil and herbaceous cover, which decreased drastically by − 34.6% and − 2.8%, respectively. As a result of tree cover increment, the average and maximum Land Surface Temperature showed a declining trend between the two periods. This study shows that increasing tree cover in line with the expansion of urbanization is inversely correlated with the land surface temperature which implies that integrating green coverage along with the built-up area can reduce heatwave in the fast growing urban areas. Therefore, the Hawassa city administration should set tree cover targets to achieve the desired balance between green and grey infrastructure and enhance the climate resilience level of the study area.

Green-blue infrastructure in the built environment – sustainable and resource-saving designs for urban structures and open spaces

Urban grey infrastructure, as it generally consists of monofunctional, sealed, impervious, heating up and reflecting surfaces, has led to a series of serious challenges (urban heat stresses, loss of biodiversity, flood risks and natural hazards) decreasing urban resilience. Ongoing construction activities result in irreversible soil consumption and loss of its numerous and vital functions. However, a common understanding has been evolving that the establishment of green-blue infrastructure (GBI) supports compensating for functional losses, as they are integrative and provide pervious, absorbent, shading and non-heating up surfaces. We present a concept to holistically interconnect stand-alone approaches to improve and support constructional design for transforming green open spaces addressing specifically urban landscape construction and building greenery. The underlying state of knowledge emerges from currently four ongoing projects on advancing GBI for re-establishing ecosystem functions and diverse habitats: 1. The Circular Soil Concept targets the reuse of excavated soil materials from construction sites to produce engineered soils. These are applied as functional vegetation substrates for landscape construction and installing building greenery, saving scarce soil resources while generating large scale and vegetated areas with climate change adaptation performance. 2. The StreetTREE-Planter is designed to install urban trees in a given street infrastructure. The advanced planter systems will support extended tree lifespans, microclimatic benefits, flood protection and urban resilience. The design is based on targeted rainwater harvesting for irrigation management in alignment with water requirements and the desired microclimatic performance. 3. The GLASGrün projects generates plant-based shading designs for glass facades. As plants and their leaves do not heat up from solar radiation, vertical greenery is promising, however challenging, for green shading of glazed surfaces and for indoor and outdoor microclimatic regulation. 4. The INReS rainwater management tool was developed as a prototype web application to integrate sustainable, plant-based rainwater management systems into BIM-(Building Information Modeling)-based construction projects. It provides up-to-date design for the wider public and specific planning guidelines. In synthesis with the present and upcoming findings of these projects, a parameter-based and BIM-compatible GBI-design management tool is foreseen to better and sustainably integrate GBI systems into construction projects, and to consider the resource question.

An ASBPA White Paper: U.S. community perspectives on coastal flooding

Coastal flooding, from both extreme events and sea level rise, is one of the top management challenges facing U.S. coastal stakeholders today. The intensity of coastal flooding is expected to increase with global sea level rise. This paper focuses on flooding challenges from the perspective of coastal communities. The myriad of flood mitigation strategies that have been implemented across the U.S. vary based on a multitude of factors including spatio-temporal scale of the coastal flooding hazard. ASBPA administered a survey of 106 coastal stakeholders from around the U.S. to assess specific community challenges and needs related to coastal flooding in late 2021. A majority of respondents indicated that their community includes an underserved population or neighborhood (54%) or nearby communities do (25%). While the vast majority of survey respondents indicated that flooding was a major challenge, only 24% of respondents’ communities have a coastal flooding adaptation plan. Improvements to drainage systems are the most commonly implemented gray infrastructure strategy in the Southeast and Gulf coast regions. Respondents from all regions noted that beach and dune restoration has been the most widely implemented nature-based flood mitigation strategy. Interest is now high in other nature-based solutions with application in low-lying, vulnerable coastal areas such as thin-layer placement on marshes, living shorelines, and hybrid projects on estuarine shorelines. This paper does not provide an exhaustive review of the science, forcings, or policies on coastal flooding in the U.S.; rather, it captures the perspectives of coastal communities and aims to inform and prioritize future research investments related to coastal flooding.

Subaqueous and Subaerial Beach Changes after Implementation of a Mega Nourishment in Front of a Sea Dike

Sandy nourishments can provide additional sediment to the coastal system to maintain its recreational or safety function under rising sea levels. These nourishments can be implemented at sandy beach systems, but can also be used to reinforce gray coastal infrastructure (e.g., dams, dikes, seawalls). The Hondsbossche Dunes project is a combined shoreface, beach, and dune nourishment of 35 million m3 sand. The nourishment was built to replace the flood protection function of an old sea-dike while creating additional space for nature and recreation. This paper presents the evolution of this newly created sandy beach system in the first 5 years after implementation based on bathymetric and topographic surveys, acquired every three to six months. A significant coastline curvature is created by the nourishment leading to erosion in the central 7 km bordered by zones with accretion. However, over the five-year period, net volume losses from the project area were less than 5% of the initial nourished sand volume. The man-made cross-shore beach profile rapidly mimics the characteristics of adjacent beaches. The slope of the surfzone is adjusted within two winters to a similar slope. The initially wide beaches (i.e., up to 225 m) are reduced to about 100 m-wide. Simultaneously, the dune volume has increased and the dune foot migrated seaward at the entire nourished site, regardless of whether the subaqueous profile gained or lost sediment. Our results show that the Hondsbossche Dunes nourishment, built with a natural slope and wide beach, created a positive sediment balance in the dune for a prolonged period after placement. As such, natural forces in the years after implementation provided a significant contribution to the growth in dune volume and related safety against flooding.

Evaluation of Systems and Technologies Of Underground Pipeline Gallery, Haikou

As the urban areas become denser, the built environment and land resources have limited the scope for further development of the urban areas. Haikou, as one of ten pilot cities to develop underground space, is chosen as the case in this study. Haikou Underground Pipe Gallery is a current underground building structure system that maximizes the utilization rate of land. This study investigates and analyzes the most useful and valuable technologies and systems of the Underground Pipe Gallery by survey and research. The result shows that U-shape construction technology is the most beneficial one and the electrical system is the largest and most widely used one. There are four high-tech applications in the electrical system: load power supply, construction of electrical distribution, power supply cable, and lighting facilities. In addition, a combination of green (sponge project), blue (water control) and gray (underground pipe network) infrastructure is utilized to create an optimal drainage system. It has made good use of the large area of urban green space and rainwater storage facilities.

Improvement of phosphorus removal in bioretention cells using real-time control

ABSTRACT Retrofitting urban watersheds with wireless sensing and control technologies will enable the next generation of autonomous water systems. While many studies have highlighted the benefits of real-time controlled gray infrastructure, few have evaluated real-time controlled green infrastructure. Motivated by a controlled bioretention site where phosphorus is a major runoff pollutant, phosphorus removal was simulated over a range of influent concentrations and storm conditions for three scenarios: a passive, uncontrolled bioretention cell (baseline), a real-time controlled cell (autonomous upgrade), and a cell with soil amendments (passive upgrade). Results suggest the autonomous upgrade matched the pollutant treatment performance of the baseline scenario in half the spatial footprint. The autonomous upgrade also matched the performance of the passive upgrade; suggesting real-time control may provide a ‘digital’ alternative to existing, passive upgrades. These findings may help site- and cost-constrained stormwater managers meet their water quality goals.

Nature-Based Solutions in “Forest–Wetland” Spatial Planning Strategies to Promote Sustainable City Development in Tianjin, China

Nature-based solutions are some of the most effective strategies to promote sustainable city development; however, existing research on NbS is mostly comprised of single variable studies rather than multiple variables. The purpose of this study was to explore the possibility of extending the NbS of a single variable to two variables for the better development of sustainable cities. Both forestation and wetland restoration are regarded as NbS for sustainable city development. The research approach of “forest–wetland” NbS was proposed and centers on the process and core issues of traditional NbS. Taking Tianjin as an example, the spatial patterns of forests and wetlands, correlation between the spatial distribution of forests and wetlands, and spatial correlation between the areas of forest growth and wetland growth within a certain distance in different years were studied using a spatial distribution pattern analysis, geographic concentration analysis, kernel density estimation and spatial autocorrelation analysis. Based on the core issues of NbS and the above spatial analysis, a “forest–wetland” spatial planning strategy was formulated. The main conclusions are as follows: forest and wetland were negatively correlated in the whole area of Tianjin, forest resources w mainly located in north, while wetland resources were mainly located in south. Compared with forests, the spatial distribution of wetlands in Tianjin was more balanced. There exist synergy and trade-offs between forest and wetland area under certain circumstances. Growth of forests was positively correlated with the growth of wetlands, within a distance of 0–400 m from 2000 to 2010, and within a distance of 0–600 m from 2010 to 2020. An increase in forest area will lead to an increase in evaporation, which in turn will hinder the growth of wetlands in Tianjin. Forest–wetland ecological network could promote synergistic between forest and wetland, and grey infrastructure to reduce potential trade-off between forest and wetland.

Integrated Land Use and Urban Function Impacts on Land Surface Temperature: Implications on Urban Heat Mitigation in Berlin with Eight-Type Spaces

• This study proposes a new categorization of land uses, the eight-type spaces (ETS). • The ETS integrates land functions into urban human-natural systems. • Spatial compositions have a distinct impact on the LST of the ETS. • Human systems and natural systems have a difference in hot spot areas. • To mitigate temperature, human systems need more attention in urban planning. The planning for cooling cities is crucial for sustainable development under the influence of climate change. However, urban warming mitigation across human-natural systems is scarce. This research aims at characterizing land surface temperature with the integration of land uses and land function with the eight-type spaces, including human systems (H1 residential area, H2 commercial area, H3 public service, H4 open space) and natural systems (N5 natural green, N6 farmland, N7 brownfield, N8 water). We seasonally investigated the LST, its correlation with three indices of spatial components. From the results, NDVI had more impact on LST than NDBI in H1, H3, H4, N6, N7, and N8; while NDBI had more influence than NDVI in H2 and N5; The area of Hot and Very hot classes in human systems is higher than in natural systems. It reveals that mitigating temperature across different urban land use types requires different management of green, grey, and blue infrastructures. The eight-type spaces could explain there are different NDVI and NDBI influences on urban temperature. More attention on urban planning is needed on human systems though increasing building height and combining grey infrastructures with green infrastructures and natural systems requiring decreasing impervious spaces for cooling cities.

Innovations in Urban Green and Blue Infrastructure: Tackling local and global challenges in cities

Traditional engineering approaches alone (gray infrastructure) are not able to meet all the challenges of sustainability posed by growing urban population and consumption. Urban Green and Blue Infrastructure (GBI) can provide cost-effective treatments, and help the achievement of several Sustainable Development Goals (SDGs). However, knowledge concerning how to innovate GBI strategically in cities remains limited. Together with the others in the special issue, this article aims to enhance understanding of the potential of city-based GBI to tackle local and global challenges practically, and provide theoretical discussions on sustainable transitions and future research on urban GBI. Via envisioning and implementation of integrated urban innovations for GBI, the ecosystem services derived from these nature-based solutions can contribute directly and indirectly to SDG achievement at various scales by increasing water and food security, reducing energy consumption, as by supporting urban biodiversity, health, and life quality. GBI can also contribute to discussions related to such emerging concepts as circular economy, urban transitions, and smart cities.