Sustainable urban water management initiatives are increasingly required to combat rapid urbanization and climate pressures. Initiatives include the role of tree planting, for which there is a need for strong evidence of benefits and drawbacks to support effective future planning. We report on the robustness of evidence from an assimilated database of urban hydrological impact studies which often had differing primary purposes. Consistent impacts were found at the local level, with trees reducing runoff and infiltration. Despite the consistency of evidence, much is undermined by the studies being somewhat lacking in robustness and scientific rigour. Many studies lack adequate controls, and models are often not strongly tested against observations. Moreover, evidence of impact at larger scales is lacking. Effects of  tree characteristics were also investigated, such as maturity and species (for which evidence is consistent and detailed) and arrangement (for which there is less evidence). Realizing the full potential of trees in urban water management decision-making would benefit from more rigorous evidence.

Urbanisation processes inherently influence land cover (LC) and have dramatic impacts on the amount, distribution and quality of vegetation cover. The latter are the source of ecosystem services (ES) on which humans depend. However, the temporal and thematical dimensions are not documented in a comparable manner across Europe and China. Three cities in China and three cities in Europe were selected as case study areas to gain a picture of spatial urban dynamics at intercontinental scale. First, we analysed available global and continental thematic LC products as a data pool for sample selection and referencing our own mapping model. With the help of the Google Earth Engine (GEE) platform and earth observation data, an automatic LC mapping method tailored for more detailed ES features was proposed. To do so, differentiated LC categories were quantified. In order to obtain a balance between efficiency and high classification accuracy, we developed an optimal classification model by evaluating the importance of a large number of spectral, texture-based indices and topographical information. The overall classification accuracies range between 73% and 95% for different time slots and cities. To capture ES related LC categories in great detail, deciduous and coniferous forests, cropland, grassland and bare land were effectively identified. To understand inner urban options for potential new ES, dense and dispersed built-up areas were differentiated with good results. In addition, this study focuses on the differences in the characteristics of urban expansion witnessed in China and Europe. Our results reveal that urbanisation has been more intense in the three Chinese cities than in the three European cities, with an 84% increase in the entire built-up area over the last two decades. However, our results also show the results of China’s ecological restoration policies, with a total of 963 km2 of new green and blue LC created in the last two decades. We proved that our automatic mapping can be effectively applied to future studies, and the monitoring results will be useful for consecutive ES analyses aimed at achieving more environmentally friendly cities.

This paper explores how varied systems of governance work at the European city level to deliver different policy mixes for implementing nature-based approaches which support integrated water management and policy. Urban systems provide unique insights here due to the concentration of consumption, economic activities and excessive land-use pressures. However, few studies are providing generic insights, rooted in policy and political theory perspectives, on the dynamic impact of urban governance systems on different mixes of policies to integrate urban nature and water management approaches. The paper fills this gap through an extensive literature review. It first draws on analysis that focuses on institutional logics of operation to understand how urban institutional arrangements of governance shape the framing of the policy problem and how this influences the choice of policy approaches. It then explores the related administrative processes including decision support tools, participatory approaches, and funding regimes. These administrative approaches deliver, potentially, different policy responses that take into account integrated nature-based policy approaches to urban water governance.

Nature-based solutions (NBS) offer multiple solutions to urban challenges simultaneously, but realising funding for NBS remains a challenge. When the concept of NBS for societal challenges was first defined by the EC in 2017, financing was recognised as one of the major challenges to its mainstreaming. The complexity of NBS finance has its origin in the multiple benefits/stakeholders involved, which obscures the argument for both public and private sector investment. Since 2017, subsequent waves of EU research- and innovation-funded projects have substantially contributed to the knowledge base of funding and business models for NBS, particularly in the urban context. Collaborating and sharing knowledge through an EU Task Force, this first set of EU projects laid important knowledge foundations, reviewing existing literature, and compiling empirical evidence of different financing approaches and the business models that underpinned them. The second set of EU innovation actions advanced this knowledge base, developing and testing new implementation models, business model tools, and approaches. This paper presents the findings of these projects from a business model perspective to improve our understanding of the value propositions of NBS to support their mainstreaming.

Interrelationships between urban and rural areas are fundamental for the development and safeguarding of viable future living conditions and quality of life. These areas are not well-delineated or self-sufficient, and existing interrelations may privilege one over the other. Major urban challenges facing China and Europe are related to changes in climate, environment, and to decision-making that makes urban and rural landscapes more susceptible to environmental pressures. Focusing on the six European and Chinese cities and surrounding rural areas, under study in the joint EC and MOST-funded REGREEN project, we examine how nature-based solutions (NBS) may assist in counteracting these pressures. We explore urban-rural dependencies and partnerships regarding NBS that can enhance resilience in Europe and China. We analyse differences between European and Chinese systems of governance, reflecting on the significance of the scale of research needed to understand how NBS provide benefits. We highlight interactions between differently delineated sheds (watershed, airshed, natureshed, and peopleshed), which influence the interrelationships between urban and rural areas. There may be one-way or two-way interdependence, and the impact may be uni or multi-directional. The European and Chinese solutions, exemplified in this article, tackle the nexus of environmental and peoplesheds. We discuss complex human interactions (and how to model them) that may, or may not, lead to viable and equitable partnerships for implementing NBS in cities within Europe and in China.

To safeguard the well-being of urban dwellers, it is vital to restore, protect and enhance urban green infrastructures (uGI), their related ecosystem services (ES) and the associated benefits for a large number of inhabitants. This study maps and monitors land cover between 2012 and 2018 in the fast-growing German city of Leipzig to produce precise information using OBIA and very high-resolution digital orthophotos. Based on this, this research pinpoints spatially differentiated multiple ES. Research has revealed that essential ES, which comprise regulating, socio-cultural and cultural-aesthetic services, have a multifunctional impact on the human urban habitat. The study provides insight into each ES type by evaluating specific classes of objects within the urban environment in a spatially explicit way and at a very high scale of resolution. In doing so, it illustrates variations in the provision of ES and renders visible disparities in the accessibility to uGI in Leipzig. By analysing the number and stands of trees and their respective height development, the study confirms that intensive management is successfully rejuvenating the urban forest, but also that foliage in this forest is suffering from drought. The mapping procedure reveals a high spatial and temporal variation in the rates of carbon storage. This is also the case for the provision of recreation areas which has an impact on the equitable distribution of ES to Leipzig’s inhabitants. Residential areas with a relatively high uGI on the outskirts of the city actually register lower market rents and rent growth rates than in those districts which lie closer to the city centre and have a comparably lower uGI. Thus, market rents and uGI have become decoupled in the fast growing city. In order to ensure and maintain the well-being of all residents in a fair way, fast growing cities like Leipzig must make even greater efforts in urban planning.

Urban expansion and ecological restoration policies can simultaneously affect land-cover changes and further affect ecosystem services (ES). However, it is unclear whether and to what extent the distribution and equity of urban ES are influenced by the stage of urban development and government policies. This study aims to assess the quantity and equity of ES under different scenarios in cites of China and Europe. Firstly, we used the Conversion of Land Use and its Effects at Small regional extent (CLUE-S) model to simulate future land cover under three scenarios: business-as-usual (BAU), a market-liberal scenario (MLS), and an ecological protection scenario (EPS). Then using ecosystem service model approaches and the landscape analysis, the dynamics of green infrastructure (GI) fraction and connectivity, carbon sequestration, and PM_2.5 removal were further evaluated. The results show that: (1) over the past 20 years, Chinese cities have experienced dramatic changes in land cover and ES relative to European cities. (2) Two metropolises in China, Shanghai and Beijing have experienced an increase in the fraction and connectivity of GI and ES in the long-term built-up areas between 2010 and 2020. (3) EPS scenarios are not only effective in increasing the quantity of ES but also in improving the equity of ES distribution. The proposed framework as well as the results may provide important guidance for future urban planning and sustainable city development.

Remotely sensed land surface temperature (LST) is often used as a proxy for air temperature in urban heat island studies, particularly to illustrate relative temperature differences between locations. Two sensors are used predominantly in the literature, Landsat and Moderate Resolution Imaging Spectroradiometer (MODIS). However, each has shortcomings that currently limit its utility for many urban applications. Landsat has high spatial resolution but low temporal resolution, and may miss hot days, while MODIS has high temporal resolution but low spatial resolution, which is inadequate to represent the fine grain heterogeneity in cities. In this paper, we overcome this inadequacy by combining high spatial frequency Environmental Services (ES), Landsat‐driven Normalized Difference Vegetation Index (NDVI), and MODIS low spatial frequency background LST at different spatial frequency bands (spatial spectral composition). The method is able to provide fine scale LST four times daily on any day of the year. Using data from Paris in 2019 we show that (1) daytime cooling by vegetation reaches a maximum of 30 °C, above which there is no further increase in cooling. In addition, (2) the cooling is relatively local and does not extend further than 200 m beyond the boundary of the NBS. This model can be used to quantify the benefits of NBS in providing cooling in cities.

Noise pollution from road traffic is ubiquitous in modern cities and is the second greatest environmental risk to health in Western Europe. Urban woodland can provide substantial noise mitigation if located properly, yet such considerations are often absent from the urban planning process. Current approaches for quantifying this important ecosystem service (ES) do not account adequately for important spatial factors and are unable to identify effectively the best locations to place new woodland for noise mitigation. We present new methods, in which we exploit the concept of least-cost-distance, to map and value the mitigating effect of urban woodland, and to identify optimal locations to place new  woodland. Applying these methods, we show that urban woodland currently provides Birmingham City (UK) with over GBP 3.8  million in noise mitigation benefits, annually. We also show that our new ‘opportunity’ mapping methods effectively identify the best locations for new woodland, achieving close to a maximum  service with less than a quarter of the additional woodland needed to achieve it. This has important implications for the design and implementation of urban tree planting for noise mitigation, and these methods can be adapted for other ES, allowing consideration of multiple service outcomes.

The benefits of urban green and blue infrastructure (UGI) are widely discussed, but rarely take into account local conditions or contexts. Although assessments increasingly consider the demand for the ecosystem services that UGI provides, they tend to only map the spatial pattern of pressures such as heat, or air pollution, and lack a wider understanding of where the beneficiaries are located and who will benefit most. We assess UGI in five cities from four continents with contrasting climate, socio-political context, and size. For three example services (air pollution removal, heat mitigation, accessible greenspace), we run an assessment that takes into account spatial patterns in the socio-economic demand for ecosystem services and develops metrics that reflect local context, drawing on the principles of vulnerability assessment. Despite similar overall levels of UGI (from 35 to 50% of urban footprint), the amount of service provided differs substantially between cities. Aggregate cooling ranged from 0.44 °C (Leicester) to 0.98 °C (Medellin), while pollution removal ranged from 488 kg PM2.5/yr (Zomba) to 48,400 kg PM2.5/yr (Dhaka). Percentage population with access to nearby greenspace ranged from 82% (Dhaka) to 100% (Zomba). The spatial patterns of pressure, of ecosystem service, and of maximum benefit within a city do not necessarily match, and this has implications for planning optimum locations for UGI in cities.

Urban greenery in cities is important for human health, for resilient and sustainable cities, and for flora and fauna. The importance of urban greenery is highlighted in numerous global, national and local policies. However, the rapid increase of urban sprawl and densification globally has reduced access, availability and quality of urban greenery. According to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), cities “do not know how to incorporate nature and nature contribution to people into city planning”. Perhaps this limitation is because urban planners, architects, landscape architects (urban designers) and urban ecologist (nature conservationist) view nature in cities differently. In addition, few studies on cities focus on nature and ecology. In this paper, we highlight the need to develop new designs and nature conservation approaches that promote biodiversity in cities. Science fiction (SF) and science have a history of inspiring each other and inspiring innovative solutions. For example, SF blockbusters have affected people’s engagement in climate change. Here, we evaluate how 44 of the most viewed American SF movies depict nature in cities, including diversity of species and how characters interact with nature. We reveal that these movies tend to ignore nature in their depictions of future cities. If nature is depicted in SF it is very similar to contemporary cities with monoculture lawns and ornamental gardens. Moreover, SF movies do not depict innovative ways of including nature in cityscapes, they illustrate unrealistic settings without basic ecological functions (e.g., pollinators), and their characters do not interact with nature when nature is depicted or only frame the scene as a façade. We suggest that urban designers, urban ecologists, and SF artists collaborate to imagine how to integrate nature and biodiversity into the depictions of future cities, a strategy that could help change norms about urban greenery.

Urban Green Infrastructure (GI) provides multiple benefits to city inhabitants and can be an important component in nature-based solutions (NBS), but the ecosystem services that underpin those benefits are inconsistently quantified in the literature. There remain substantial knowledge gaps about the level of service supported by less studied GI types, e.g. cemeteries, or less-studied ecosystem services, e.g. noise mitigation. Decision-makers and planners in cities often face conflicting or incomplete information on the effectiveness of GI, particularly on their ability to provide a suite of co-benefits. Here, we describe a feature-based typology of GI which combines elements of land cover, land use and both ecological and social function. It is consistent with user requirements on mapping, and with the needs of models which can conduct more detailed ecosystem service assessments which can guide NBS design. We provide an evidence synthesis based on published literature, which scores the ability of each GI type to deliver a suite of ecosystem services. In the multivariate analysis of the typology scores, the main axis of variation differentiates between constructed (or hybrid) GI types designed primarily for water flow management (delivering relatively few services) and more natural green GI with trees, or blue GI such as lakes and the sea, which deliver a more multi-functional set of regulating services. The most multi-functional GI on this axis also score highest for biodiversity. The second element of variation separates those GI which support very few cultural services and those which score highly in enabling physical wellbeing and social interaction and, to a lesser extent, restoring capacities. Together the typology and multi-functionality matrix provide a much needed assessment for less studied GI types, and allow planners and decision-makers to make a-priori assessments of the relative ability of different GI as part of NBS to address urban challenges.

Cities are highly complex, inter-connected social-ecological systems, encompassing social, built and natural/semi-natural components. They interact with their surrounding extra-urban areas at varying scales, from peri-urban and rural to global. Space is a valuable commodity in cities. However, in most instances, city planners tend to think about interventions only within cities and rarely about the wider connected domains outside. Yet, considering the wider spatial context, including space outside of the city boundaries, may open up opportunities to achieve substantially greater benefit for city residents without sacrificing valuable space, leading to more sustainable city design for people and the environment. In this paper we discuss the intra-extra-urban flows which connect cities to their wider airsheds, watersheds, biosheds and resourcesheds, which in turn interact with their peoplesheds. For each domain, we illustrate the processes and the scales they operate at, and discuss the implications for optimum location of nature-based solutions (NBS) to address urban challenges. We suggest that integrating knowledge about these multiple sheds can inform holistic design of NBS to deliver greater benefit for city residents. This takes into account the synergies and multi-functional co-benefits which arise from a careful consideration of place and people, while minimising potential disbenefits and trade-offs.

Le concept de solutions fondées sur la nature est issu de la rencontre des sciences de l’écologie et des sciences économiques et se concrétise par une diversité de projets opérationnels ayant pour but de faire face aux défis du changement global (chaleur urbaine, perte de biodiversité, inondation, pollution de l’air) et autres maux de notre société (déconnexion à la nature, santé, bien-être, alimentation). Pour l’espace mégarégional, qui comprend des zones d’urbanisation très denses ainsi que des zones de biodiversité à préserver, ces solutions fondées sur la nature répondent à des problématiques à long terme. Plusieurs projets ont déjà vu le jour en région Île-de-France, mais restent encore discrets par rapport à l’ampleur du défi.

Urban green space (UGS) has gained increasing attention due to its environmental and social functions. However, the compound effects of climate change, population growth and economic development on UGS are largely unknown. We selected 107 medium-sized and large cities in China to investigate dynamics in the spatial pattern of UGS in relation to government policy and other drivers based on remote sensing data for the period 1990 to 2019. To explore the effect of different levels of urbanization on changes in green space, we develop a new Normalized Urban Development Index (NUDI) to classify urban-suburban-rural gradients, viz. Long-term Built-up, New Built-up and Non-Built-up. Then, we analysed changes over time in the annual peak value of fraction of vegetation cover (FVC) for 380,000 cloud-free Landsat images, and regional UGS dynamics were evaluated using the proposed Regional Greenness Dynamic Index (RGDI). Finally, to reveal the major driver(s) of changes in UGS and estimate the extent to which patterns of urban greening are due to differences in economic development, we compared the observed UGS spatio-temporal dynamics with data on several climatic, social-economic and land use related factors for the same period. The NUDI are shown to be highly effective in mapping urban development gradients, with overall accuracy in the identified classes of 89%. Annual maximum FVC analysis indicates that there was significant greening between 1990 and 2019 in both the long-term built up (10,667.52 km2) and the non-built up areas (529,310.47 km2), while there was a major increase in browning (25,110.43 km2) in the newly built-up areas. The RGDI results indicate that 65% (71/107) of long-term built-up areas in cities trended greener over 2010 to 2019 under consideration. At the whole city scale, RGDI is negatively correlated with gross domestic product (GDP), although when considering the long-term built-up areas only, economic growth exhibits a significant positive correlation during 2010 to 2019 (R = 0.62, p < 0.01). This study offers important insights as to the patterns of change in urban greening extent over time and its underyling drivers across urban-suburban-rural gradients against the background of urban expansion, afforestation, climate change and economic development.