International Perceptions of Urban Blue-Green Infrastructure: A Comparison across Four Cities

Blue-Green infrastructure (BGI) is recognised internationally as an approach for managing urban water challenges while enhancing society and the environment through the provision of multiple co-benefits. This research employed an online survey to investigate the perceptions of BGI held by professional stakeholders in four cities with established BGI programs: Newcastle (UK), Ningbo (China), Portland (Oregon USA), and Rotterdam (The Netherlands) (64 respondents). The results show that challenges associated with having too much water (e.g., pluvial and fluvial flood risk, water quality deterioration) are driving urban water management agendas. Perceptions of governance drivers for BGI implementation, BGI leaders, and strategies for improving BGI uptake, are markedly different in the four cities reflecting the varied local, regional and national responsibilities for BGI implementation. In addition to managing urban water, BGI is universally valued for its positive impact on residents’ quality of life; however, a transformative change in policy and practice towards truly multifunctional infrastructure is needed to optimise the delivery of multiple BGI benefits to address each city’s priorities and strategic objectives. Changes needed to improve BGI uptake, e.g., increasing the awareness of policy-makers to multifunctional BGI, has international relevance for other cities on their journeys to sustainable blue-green futures.


Ningbo, China
Ningbo is a major port and industrial hub, situated southeast of the Yangtze River Delta in Zhejiang province. The 2020 population is c. 7.5 million and projected to reach 10 million by the 2030s. Ningbo is sensitive to seasonal climatic effects, particularly in the wet season when cyclonic storms (typhoons), tidal surges and intense rainstorms frequently visit the region (Chan et al., 2012). More than 44 typhoons are estimated to have impacted the city since the 1950s, causing 12 large floods and a total economic impact exceeding 93 billion RMB (Tong et al., 2007). Typhoon Fitow (October 2013), exhibiting a maximum 24-hr rainfall of 263mm, caused widespread pluvial flooding as runoff overloaded the city's drainage network (currently designed for 1-in-5 to 1-in-20 year events), affecting over 2.4 million people (Tang et al., 2015).
The outdated drainage systems in Ningbo (and many other Chinese cities) currently operate in exceedance of their design standards, and are unable to cope with the combination of rapid urbanization, reduction in permeable greenspace, and high intensity of cyclonic-enhanced rainstorms (Chan et al., 2018). The Sponge City Program (SCP) was initiated by the Chinese Government in 2013 to tackle these urban water challenges; mitigating flood risk while storing water to meet future demand by retrofitting existing cities with BGI to facilitate the absorption of rainwater and subsequent storage, purification and reuse (MHURD, 2014). The SCP is founded on pilot projects in demonstration zones within the 30 cities selected to trial this approach (Qiao et al., 2019). Participating cities must ensure that 20% of their urban land includes 'sponge' features (e.g. rain gardens, swales, wetlands, ponds, and permeable paving) by 2020, and 70-85% annual precipitation should be managed onsite.
Strategies will improve stormwater management capacities from current low standards (1-in-1 to 1in-5 year events) to 1-in-30 year events (ibid.). The SCP is being delivered within an urban governance framework that promotes development and urbanization in tandem with improving the natural environment and maintaining pre-development hydrological flow regimes (Jiang et al., 2017).

Rotterdam, the Netherlands
As a low-lying port city situated in the Rhine-Meuse Delta, Rotterdam has a close connection with water; approximately 85% of the city is up to 7m below sea level and the remaining 15% lies in unembanked areas (City of . Increasing the city's resilience to the impacts of future climate change (notably rising sea levels and flooding from extreme rainfall events) is a key priority as outlined in the Rotterdam Climate Change Adaptation Strategy (City of  and subsequent Rotterdam Resilience Strategy (City of Rotterdam, 2016). A multi-layer-safety approach has been adopted and focuses on three key aspects: 1) maintaining and strengthening existing infrastructure (dykes, barriers, sewers), 2) redesigning the city to create more space for water storage by promoting BGI, and 3) working with other city projects to link adaptation and spatial planning (Ministry of Infrastructure and the Environment, 2015). Multifunctional space, multiple beneficiaries, and multi-agency partnerships and funding are key, as is using urban water policy to help improve the quality of life of city residents (de Graaf and van der Brugge, 2010).
Over the last two decades, Rotterdam has produced numerous reports and guidance to support the transition to greater climate resilience, founded on the 2007 ambition to become 100% climate-proof by 2025 (maintaining functionality of the economic and social systems in the city with minimal disturbance during extreme weather events) (Municipality of Rotterdam, 2007). Waterplan 2working on water for an attractive city, progressed from the 2001 Waterplan by focussing on sustainability and adaptation at the scale of the Rotterdam Metropolitan Region. The 3 rd edition of Rotterdam's Waterplan (2013) comprises 13 sub-water plans in accordance with the urban typologies of the city (Municipality of . Rotterdam Weather-Wise (Rotterdam Office of Climate Adaptation, 2019) can be considered the 4 th edition of Rotterdam's Waterplan. This promotes a bottom-up approach, involving both public and private actors, and focuses on small scale measures that will increase the city's resilience to future climate change impacts while improving outdoor public spaces. This development is increasingly visible in the city, including several water squares, extensive BGI, depaving projects, 220,000 m 2 of green roofs, and a rooftop park functioning as flood defence (Buro Sant en Co, 2014).

Portland, Oregon, USA
Portland is located near the confluence of the Columbia and Willamette Rivers. The city of Portland, with a population of around 653,000 (United States Census Bureau, 2019), is the largest of the twentyfour cities in the region's urban growth boundary (UGB). UGB's are required around each city and metropolitan area in Oregon to protect farm and forest lands from development (Metro, 2014). This model of compact development has led to Portland being recognized as a world leader in smart growth (Mohammed et al., 2016).
Portland's climate has two distinct seasons-a wet season from October-March when approximately 70% of precipitation falls, and a dry season from April-September (Fahy et al., 2019). Substantial investments have been made by government agencies, nonprofits, and private landowners to reduce nuisance flooding, improve water quality, and enhance fish habitat. system of green streets. These investments are expected to decrease discharges from the combined sewer system into the Willamette River from fifty times per year to an average of four times each winter and once every third summer (Netusil et al., 2014). The 'Gray to Green' initiative invested widely in BGI implementation to alleviate loadings on the piped infrastructure system and reduce adverse impacts on urban watercourses. These ongoing efforts have, to date, delivered over 900 green streets (bioswales), more than 400 ecoroofs, over 32,000 street trees, and invested in widespread culvert replacement or removal; purchasing of properties at high flood risk from willing sellers, and; reconnected and restored urban streams, floodplains and native vegetation (BES, n.d). In 2018, the City Council adopted one of the most aggressive green-roof policies in the United States that requires any new buildings with a net building area of 20,000 square feet or more to have a green roof. As of 2019, there were almost 1.4 million square feet of green roofs in the city of Portland (Netusil and Thomas, 2019). Figure S1. Survey home page with language selection box in the top right.

Survey Questions
In several questions, respondents were asked to rank from 'very significant' to 'very insignificant'. Here, we present the exact language used in the survey. However, for clarity, in the manuscript and the statistical analysis in Supplementary Material C, e.g., Table C.2., we use the term 'significant' in a statistical sense and report perceptions of significance from the survey as perceptions of relative 'importance'.
1. What do you think are significant water challenges in your City? Please give each challenge a score from 1 (very significant) to 10 (not significant). The challenges interrelate through already existing complex (infrastructure) networks.

R4
Important is not the same as a substantial (big) risk… the above is filled in according to importance.
Question 3. Who are leading the way in implementing Blue-Green infrastructure in your City, and who should lead the way?
Respondent ID 'Other' response -who are leading the way N22 Ministry of Housing and Construction Bureau N29 Some of the stakeholders listed should participate but not necessarily lead. N7 Government initiate legislation for the rewards and punishments measures to control the private developers to implement the Blue-Green infrastructure NE2 Landowners, land agents, surveyors, planning/engineering/landscaping consultants, NE24 no one organisation is leading the way -it is more via partnerships leading P10 We don't have private water or sewer authorities so not ranked. P11 The City/Agencies were definitely leading but it's become less of a priority. P17 marked for both in cases where some individuals are leading the way while others are not in the same grouping R22 Question is not entirely clear.

R24
I think everyone should contribute, no distinctions.

R34
Difficult, considering the complexity to differentiate. Area-orientated alliances and programming should be leading.

R7
Housing corporations should be involved considering they own/manage large portion of properties.

Question 4. Which are the most effective factors for driving Blue-Green infrastructure implementation?
Respondent ID 'Other' response -who are leading the way N29 I think these may be regional specific. In China, national initiative from the central government would still be the most influential factor to drive any infrastructure building while local government would have the knowledge and capital on the ground to implement it. PPP is now a fashion but it still needs to be driven from the government. Money.

R5
Courage to deviate/ to think freely + sufficient resources for realisation and operation. Table S1. Ranking of the water challenges identified by the whole sample population and for each case study city. The values represent the median ranking for each water challenge. Lower rankings denote greater importance of the challenge. The most important challenges for each group are highlighted in grey. Water challenges that have (statistically) significantly different rankings between one or more cities are listed in the final column.   Table S3. Testing for statistically significant differences between respondents' disciplinary backgrounds and perceptions of the very important benefits of Blue-Green Infrastructure (BGI). Disciplinary backgrounds include: Engineering, Environmental Management, Implementation, Landscape Architecture or Design, Planning, and Strategy and Policy/Finance (see Table 1).