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

Abstract

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 (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.

Full text

Water 2021, 13, 544. https://doi.org/10.3390/w13040544 www.mdpi.com/journal/water
Article
International Perceptions of Urban Blue-Green Infrastructure:
A Comparison across Four Cities
Emily C. O′Donnell
1,
*, Noelwah R. Netusil
2
, Faith K. S. Chan
3,4
, Nanco J. Dolman
5
and Simon N. Gosling
1
1
School of Geography, University of Nottingham, Nottingham, NG7 2RD, UK; simon.gosling@notting-
ham.ac.uk
2
Department of Economics, Reed College, Portland, OR 97202-8199, USA; netusil@reed.edu
3
School of Geographical Sciences, Faculty of Science and Engineering, University of Nottingham Ningbo
China, Ningbo 315100, China; faith.chan@nottingham.edu.cn
4
School of Geography & Water@Leeds Research Institute, University of Leeds, Leeds LS2 9JT, UK
5
Royal HaskoningDHV, 1090 GE Amsterdam, The Netherlands; nanco.dolman@rhdhv.com
* Correspondence: emily.o’donnell@nottingham.ac.uk; Tel.: +44-(0)-115-846-8137
Abstract: 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 mul-
tiple 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 (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.
Keywords: blue-green infrastructure; perceptions; climate change adaptation; urban water manage-
ment; resilience; multiple benefits
1. Introduction
Blue-Green Infrastructure (BGI) is increasingly recognised and valued as a strategy
to address the urban water challenges posed by present-day climate variability and ur-
banisation, and to increase the resilience of cities to future change [1–8]. At the same time,
BGI can enrich society and the environment through the provision of multiple co-benefits
[9–12]. International cities are gradually evolving from a sole reliance on centralised grey
infrastructure towards decentralised facilities that use BGI to retain, attenuate, store and
reuse surface water on site, increasing their resilience to future environmental threats
[13,14]. This fundamental change in how cities manage water is driven by increasingly
frequent and extreme rainfall events, drier summers, accelerating urbanisation, and re-
ductions in public green spaces that lead to water challenges such as flooding, water scar-
city, over-exploitation of groundwater, water pollution, maladaptive drainage systems
and wasting of rainwater resources [15,16]. Approaches centred on ‘living with and mak-
ing space for water’ [17,18] and water-sensitive urban design [19], founded on the incor-
poration of multifunctional blue, green and grey infrastructure in urban development and
Citation: O′Donnell, E.C.; Netusil,
N.R.; Chan, F.K.S.; Dolman, N.J.;
Gosling, S.N. International Percep-
tions of Urban Blue-Green Infra-
structure: A Comparison across Four
Cities. Water 2021, 13, 544.
https://doi.org/10.3390/w13040544
Academic Editor: Vassilis Glenis
Received: 28 January 2021
Accepted: 17 February 2021
Published: 20 February 2021
Publisher’s Note: MDPI stays neu-
tral with regard to jurisdictional
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tutional affiliations.
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and con-
ditions of the Creative Commons At-
tribution (CC BY) license (http://cre-
ativecommons.org/licenses/by/4.0/).

Water 2021, 13, 544 2 of 25
retrofit projects, are increasingly adopted internationally to address the full water spec-
trum (floods to droughts) and tackle social, economic and environmental challenges
[20,21]. Implementation of BGI is further driven by the need to mitigate urban heat [22]
and increase the value of urban natural capital [10].
BGI is defined as an interconnected network of landscape components, both natural
and designed, that includes open, green spaces and water bodies (ephemeral, intermittent
and perennial) which provide multiple functions [23,24]. Often referred to as green infra-
structure (GI) or nature-based solutions (NBS), BGI is subtly different in that it is specifi-
cally designed to turn ‘blue’ (or ‘bluer’) during rainfall events to manage stormwater and
reduce flood risk [24,25]. BGI assets include green roofs and walls, swales, rain gardens,
street trees, ponds, urban wetlands, restored watercourses, reconnected floodplains, and
re-naturalised and de-culverted rivers [7,26]. Healthy riparian areas in urban environ-
ments are also acknowledged as BGI assets that provide opportunities for environmental
enhancement and recreation, and represent an ecological network connecting (physically,
visually and ecologically) BGI in urban areas with surrounding natural areas and blue-
green space [27,28]. Interlinked are soil and water bioengineering approaches, whereby
plants are used alone or in combination with structural materials [29] and play a key role
in the design of sustainable NBS and BGI [30].
Multifunctionality and the provision of multiple co-benefits is fundamental to the
growing appeal of BGI [7,31] as is the recognition that many of the unintended, adverse
side effects of grey infrastructure can be avoided by leveraging natural processes and eco-
system services [32]. As [7] summarise, BGI can reduce the impacts of climate change by
mitigating risks associated with extreme storms, droughts and heatwaves; improve water
security, air and water quality; enhance wildlife and biodiversity; increase urban green-
space and landscape connectivity; improve physical and mental health and wellbeing;
create attractive landscapes and positive placemaking; support sustainable water resource
management, and lengthen the service provision of ageing grey infrastructure currently
operating beyond its design life [9,12,31,33].
This study approaches the issue of BGI perceptions in a unique way by exploring
explicit perceptions of BGI in four cities at the forefront of BGI implementation, through
an online survey with professionals from a range of disciplines (engineers, environmental
managers, designers, planners, and those involved in strategy, policy, finance and imple-
mentation) and organisations (public, private, academia, nonprofits). To our knowledge,
this is the first multi-country comparison of professional stakeholders’ perceptions of BGI,
supported by a detailed online survey and supplementary analysis of open-source plans,
reports and city strategies.
2. Perceptions of BGI
Despite extensive knowledge of the multiple benefits, BGI is often designed to deliver
a primary benefit, typically stormwater management [34]. Numerous socio-political, tech-
nical and institutional barriers further obstruct implementation [25,35–37]. Low uptake of
BGI is compounded by unfavourable policies and governance, limited resources, famili-
arity with, and preference for, traditional infrastructure, low awareness, and perceptions
of higher costs, complex maintenance regimes and enhanced risk [38,39]. Understanding
perceptions of BGI in the public realm is a fundamental step towards designing infrastruc-
ture that is understood (e.g., awareness of the functionality and delivery of multiple co-
benefits), accepted, and desired by communities, practitioners and decision-makers
[39,40].
Research into the perceptions of BGI typically focuses on residents and communities
living with the assets (e.g., [40–43]). There are currently few studies that explore profes-
sional stakeholders’ (i.e., those involved in planning, designing, implementing and man-
aging urban flood risk and water management programs) perceptions of the challenges
and opportunities associated with BGI. Ref. [21] found that perceptions of BGI (specifi-
cally, green stormwater infrastructure) in two geographically proximal regions (Portland,

Water 2021, 13, 544 3 of 25
Oregon, and Clark County, Washington) differed extensively due to the distinct socio-
political climates and city-specific drivers for BGI; the opportunistic approach in Portland
contrasted with greater caution and more risk-averse BGI planning and delivery in Clark
County. New York City practitioners have suggested that changes in management re-
gimes are needed to improve the value of BGI, e.g., opening up bioswales to the public to
offer recreational opportunities (active–gardening, or passive–benches) [44].
Several case studies have examined professionals’ perspectives of the barriers and
challenges to implementing BGI and how they have been overcome, e.g., in Australia [35];
Portland, Oregon USA [21,36], Sweden [45], Semarang City, Indonesia [2], China [46] and
Newcastle, UK [39]. Recent research has also compared urban water management ap-
proaches across different cities and countries to develop an understanding of the role of
BGI in urban water management, and share best practices from cities with different geo-
graphical, climatological, socio-political and governance characteristics. For example, [47]
interviewed local government officials to evaluate and compare the governance of sus-
tainable stormwater management using green infrastructure (GI) in two Chinese and two
Swedish cities, exploring the impact of non-hierarchical (Sweden) and hierarchical
(China) political systems on GI governance. In their cross-country investigation of GI-
based sustainable urban water management practices, [20]found similar drivers and chal-
lenges to GI implementation in five international cities, yet the specific role of GI in each
city dictated how it was used to meet development targets and tackle water challenges.
Similarly, [48] report different priorities for climate change adaptation within seven
midsize cities in the North Sea Region, which impacts on the value given to BGI solutions.
As with professional perceptions of BGI, there are few studies of the perceptions of
urban climate adaptation strategies, such as Urban Heat Island (UHI) mitigation and im-
plementation strategies which include BGI as a key component. Ref. [49]] found that green
infrastructure (including green roofs) was considered the most effective UHI mitigation
strategy by 56% of respondents in an international survey. In a pilot study in ten countries
worldwide, [50] explored awareness of climate adaptation strategies and found differ-
ences in awareness between countries and, moreover, between different respondent
groups, e.g., citizens, politicians, urban planners and urban climate experts. As with BGI,
greater awareness raising and best practice exemplars are of paramount importance in
rising the profile of climate adaptions strategies and increasing implementation [50].
2.1. Purpose of the Research
Perceptions of BGI held by professional stakeholders in four cities, across three con-
tinents, with established BGI programs, are examined: Newcastle (UK), Ningbo (China),
Portland (Oregon USA), and Rotterdam (Netherlands). Survey responses are subse-
quently analysed in the context of published plans, strategies and literature from each city
that relate to BGI, urban water management, or climate change adaptation agendas. Such
an approach provides new insights into how BGI is viewed by professionals working both
within, and outside of, the flood and water management discipline. This range of perspec-
tives must be understood if multifunctional BGI is to become a cornerstone of urban de-
velopment and retrofit projects.
The expected insights from our study are twofold. First, contextualised knowledge
of BGI drivers, leadership, provision of multiple benefits, and the changes needed to ena-
ble critical barriers to be overcome and improve the uptake of BGI, will be developed for
the four case study cities. This knowledge, including examples of BGI best practices and
lessons learned from recent BGI programs, will be valuable to other international cities
currently exploring the role of BGI in urban water management and climate change ad-
aptation strategies. Second, the comparison of the four cities will create a nuanced under-
standing of how the socio-political, geographical and climatological similarities and dif-
ferences between these cities influence perceptions towards BGI.
The four case study cities are first introduced, followed by a description of the meth-
ods used to collect and analyse the data. Survey results are then presented and used to

Water 2021, 13, 544 4 of 25
inform discussion of the delivery of multiple benefits by multifunctional BGI, and how
barriers to widespread implementation may be overcome by effective leadership and gov-
ernance. Limitations of the survey approach are then outlined, and the key findings of this
research into international perceptions of BGI are summarised.
3. Case Study Cities
The four cities make for an interesting comparison and were selected due to their
different drivers for urban water management, varying approaches to governance and
regulations, and different mechanisms for planning and delivery. They are also at the
forefront of BGI implementation in their respective countries and have established BGI
visions (Figure 1, Table 1, further details are provided in Supplementary Material).
Figure 1. Examples of Blue-Green Infrastructure (BGI) in the case study cities: (a) sustainable drainage pond in the New-
castle Great Park development site; (b) Ningbo eco-corridor; (c) bioswale in a residential area in Portland; (d) green tram
tracks in central Rotterdam. Photo credits: (a), (b) and (d) Emily O’Donnell, (c) Noelwah Netusil.

Water 2021, 13, 544 5 of 25
Table 1. Background information on the four case study cities. BGI (Blue-Green Infrastructure), SuDS (Sustainable Drainage Systems), CSO (Combined Sewer Overflows).
City Country Main River
Area
(km2) Population Drivers for BGI BGI Assets/Approaches
Newcastle UK Tyne 114 280,000
Improving resilience to
future flooding while
maximising the social
and environmental
benefits of managing
water above the ground
in attractive blue-green
systems
Several exemplar schemes showcase effective delivery of BGI through local and
regional partnerships, e.g., SuDS ponds in Newcastle Great Park development,
and the Killingworth and Longbenton surface water management scheme [51].
Proposed network of ‘Blue-Green corridors’ through city (Newcastle City Strate-
gic Surface Water Management Plan)[52].
Ningbo China
Yong,
Fenghua and
Yao
9816 7,500,000
Mitigating flood risk,
facilitating absorption
of rainwater and subse-
quent storage, purifica-
tion and reuse, updat-
ing current drainage
system
Sponge City Program (SCP) initiated by the Chinese Government in 2013 to
tackle urban water challenges, rapid urbanisation, and reduction in permeable
greenspace [53]. Pilot projects in 30 cities selected for the SCP trial. 20% of their
urban land should include ‘sponge’ features (e.g., rain gardens, swales, wetlands)
by 2020, and 70–85% annual precipitation should be managed onsite [47].
Portland USA
Willamette
and Columbia 375.5 653,000
Reducing nuisance
flooding, improving
water quality (e.g., by
CSO reduction), and
enhancing fish habitat
‘Grey to Green’ initiative and others have invested widely in BGI to alleviate
loadings on the piped infrastructure system and reduce adverse impacts on ur-
ban watercourses. To date, have delivered over 900 green streets (bioswales),
more than 400 ecoroofs, over 32,000 street trees, and invested in widespread cul-
vert replacement or removal; and reconnected and restored urban streams, flood-
plains and native vegetation [54].
Rotterdam The Neth-
erlands Maas 325.8 623,000
Increasing the city’s re-
silience to the impacts
of future climate
change [55].
Multi-layer-safety approach: (1) maintaining and strengthening existing infra-
structure (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 [56]. To date, there are several water
squares, depaving projects, 220,000 m2 of green roofs, and a rooftop park func-
tioning as flood defence [57].

Water 2021, 13, 544 6 of 25
Portland has one of the oldest and most successful BGI programs in the United States,
and has invested widely in BGI over the last two decades to alleviate loadings on the piped
infrastructure system, improve water quality and manage nuisance flood risk [58]. Ningbo
is one of the Chinese ‘Sponge City’ pilots, tasked with transforming urban water manage-
ment systems to promote water-resilient, low impact development integrated with urban
planning to improve the city’s capacity to function ‘like a sponge’ by absorbing rainwater
to mitigate flood risk while storing and filtering water to meet future use [14,46,59,60].
Rotterdam is a forerunner city moving towards transformative climate governance [61]
and has a long history of combining urban water management, spatial planning, and cli-
mate change adaptation to increase the city’s resilience to, for example, sea level rise and
increasing occurrence of pluvial flood events, while improving the quality of life of urban
residents [62]. Finally, BGI is a key component in Newcastle’s management plans, includ-
ing the Core Strategy and Urban Core Plan for Gateshead and Newcastle-upon-Tyne
2010–2030 [63] and Newcastle City Strategic Surface Water Management Plan [52].
4. Methods
4.1. Survey Structure and Delivery
The standard approach to survey development using focus groups to co-design the
questions and subsequently update the survey instrument after initial development by
the research project team [64] was not suitable for this study due to the limited number of
professional stakeholders working with BGI in the case study cities; the same participants
cannot be used for both focus groups and as survey participants. As with other studies of
professional stakeholder perceptions (e.g., [65,66]) the survey was developed iteratively
between the project team. Each question was carefully phrased to be unambiguous and
address a specific research question (explored in Section 5). The questions were informed
by existing literature on overcoming barriers to BGI implementation [35,36,39], percep-
tions of multiple benefits [40,43,67] and research and policy papers detailing the strategies
of the four cities [16,68,69].
The surveys were subdivided into five sections: (1) general information; (2) benefits,
beneficiaries and implementation of BGI; (3) multifunctionality and best practice; (4) col-
laboration; and (5) barriers and challenges. We report in this paper a sub-set of the survey
questions specifically selected to focus on identifying the most important water challenges
in each city; understanding what drives BGI implementation; what the perceived multiple
benefits are; who the BGI leaders are; and what strategies could improve uptake of BGI.
A combination of question types was used, including scalar (5-point scale), ranking, cate-
gorical, and multiple choice (Supplementary Material). The ranking, categorical and mul-
tiple choice questions included a free text option (‘other (please specify)’). The options in
the questions, e.g., the changes needed to improve the uptake of BGI (Section 5.5), were
decided by the researchers prior to the study. In several questions, respondents were
asked to rank from ‘very significant’ to ‘very insignificant’; however, for clarity we use
the term ‘significant’ in a statistical sense and report perceptions of ‘significance’ from the
survey as perceptions of relative ‘importance’.
The survey took approximately 15 to 20 min to complete and was launched online
through the Qualtrics XM platform. It was open from mid-March 2019 to the end of April
2019. The survey was translated into Dutch and Chinese and respondents could select
their preferred language on the survey home page (Supplementary Figure S1). Partici-
pants read a participant information sheet and granted consent prior to completing the
survey. Responses were anonymised and coded, i.e., P1 = Portland respondent 1. A sum-
mary of the methodological process is presented in Figure 2.

Water 2021, 13, 544 7 of 25
Figure 2. A flow chart summarising the main methodological stages in this study of professional stakeholder perceptions
of Blue-Green Infrastructure (BGI).
4.1.1. Participants and Response Rate
Purposive sampling was used in this geographically targeted investigation; the pro-
ject team’s expert knowledge of those working with, and knowledgeable of, BGI in the
four cities was used to select participants in a non-random manner. Twenty-one partici-
pants from each city were sent a personalised email from the research team inviting them
to complete the survey. Limiting the sampling frame to contacts of the research team is
not thought to introduce any significant bias or exclude respondents due to the team’s
detailed knowledge of BGI policy and practice in the four cities and corresponding
knowledge of the key professional players. In cases where the targeted respondent was
unable to complete the survey (due to time constraints, for example), they identified a
suitable replacement, thus broadening the sampling frame.
The small sample size in this study is primarily due to the limited number of profes-
sionals working with, and knowledgeable in, BGI, in the case study cities, especially in a
relatively small city such as Newcastle (population ~280,000). While surveys of public per-
ceptions are able to access a much larger sampling pool, i.e., typically focusing on a geo-
graphical area, such as [70] who surveyed 1750 homes in England and 2467 in Northern
Ireland in their study of community preferences around BGI (with 299 returns from Eng-
land and 329 from Northern Ireland), such a large initial sampling pool is not available
for studies of professional perceptions of BGI. The small sample size is comparable to ear-
lier investigations of professional stakeholder perceptions of BGI and water management.
For example, [39] interviewed 19 stakeholders to explore barriers to BGI implementation;
eight city managers responded to [20]’s questionnaire on urban water management and
green infrastructure; and [47] investigated governance factors of sustainable stormwater
management with 23 participants from four different cities. 72 stakeholders from 49 river
municipalities were also surveyed by [71] in an exploration of urban public services man-
agement. Participants in this study are thus deemed to be representative of the sample
population, i.e., those working with BGI in each city, and comprised professional experts
in BGI, stormwater management and/or climate change adaptation and mitigation, urban
planning, design and implementation.
The survey was initiated by all 84 invited participants. In total, 64 (76%) successfully
completed all questions. A total of 36% were from government organisations, 34% were

Water 2021, 13, 544 8 of 25
from private organisations (such as UK water companies or environmental consultancies),
17% were academics and 13% were from nonprofits (such as environmental societies,
charities and advocacy groups) (Table 2). Respondents were drawn from six disciplinary
areas with the highest proportion (39%) working in engineering. 47% of the Portland re-
spondents work in nonprofits.
Table 2. Respondents’ discipline and type of organisation (those who completed all questions). ‘Public’ typically refers to
government organisations.
City Engineering
Environmental
Management Implementation
Landscape
Architecture
or Design
Planning
Strategy,
Policy and
Finance
Total
Ningbo,
(China)
Private (3)
Public (6) Academia (3) Academia (1)
Private (1)
Academia (2)
Public (1) 17
Newcastle (UK)
Academia (2)
Private (5)
Public (2)
Nonprofits (1)
Private (1)
Public (2)
Public (1)
Academia
(1)
Private (1)
16
Rotterdam
(Netherlands)
Private (1)
Public (3) Academia (1) Private (3)
Public (1) Private (4) Public (1) Private (1)
Public (1) 16
Portland (USA) Nonprofits (1)
Public (2)
Nonprofits (3)
Public (2)
Academia (1)
Nonprofits (1)
Private (2)
Public (1)
Nonprofits
(2) 15
Percentage of
total 39% 20% 6% 17% 8% 9%
64
(100%)
4.2. Data and Statistical Analysis
The data were coded into IBM SPSS Statistics 25 software and the responses investi-
gated using descriptive statistics. Data are presented in a bar chart (Figure 3), tables with
colour scales (Figures 4 and 5), a radar chart (Figure 6) and a stacked bar chart (Figure 7).
Responses to the free text option in questions 1 (water challenges), 3 (drivers for BGI im-
plementation) and 4 (BGI leaders) are not included in the figures due to the disparity of
responses and fact that some provide additional commentary rather than a singular re-
sponse. These data are presented in Supplementary Material.

Water 2021, 13, 544 9 of 25
Figure 3. Median ranking of the water challenges by the whole sample population (n = 64). Respondents were asked to
rank the importance of each challenge in their city using a 1 (very important) to 10 (not important) scale; lower rankings
denote greater importance of the challenge. The bars are in the order of median score. *Water quality deterioration also
includes concern over river health.
Figure 4. The level of agreement between respondents in each city regarding the perception that the benefits of BGI (Blue-
Green Infrastructure) are very important or important. Values range from 0 (red, which indicate that no members of the
city group found the benefit to be very important or important) to 100 (green, which indicate that all members of the city
group found the benefits to be very important or important). RWH = Rainwater Harvesting.

Water 2021, 13, 544 10 of 25
Figure 5. Level of agreement within cities regarding what drives implementation of BGI (Blue-Green Infrastructure). Val-
ues range from 0 (red = no members of the city group selected the drivers) to 100 (green = all members of the city group
selected the drivers). Respondents could select multiple options. Physical process and risk drivers, e.g., impacts of climate
change, were not included in this question (see Supplementary Material).

Water 2021, 13, 544 11 of 25
Figure 6. Radar chart showing the perceptions of organisations and individuals that are leading the way, and who should
lead the way, in Blue-Green Infrastructure (BGI) implementation in the four case study cities (a–d) and all data (e). The
axes show the percentage of respondents that selected each group and the radii (or spokes) represent the different groups.
For example, in Newcastle, 100% of respondents thought that developers should lead the way in BGI implementation as
illustrated by the black line to the outer edge of the chart. Respondents were able to select multiple responses for both who
should lead and who are leading, explaining why the sum of the radii for each city exceed 100%. WSC (Water and Sewer-
age Companies). *Environment Agency refers to the relevant national organisation in each country, e.g., the Environment
Agency (UK), Environmental Protection Agency (USA), Ministry of Infrastructure and Water Management (Netherlands)
or the Housing and Construction Bureau (China).

Water 2021, 13, 544 12 of 25
Figure 7. The percentage of respondents in each city that regarded the changes needed to improve the uptake of Blue-
Green Infrastructure (BGI) as very important or important. The coloured stacked bars represent the four cities as per the
legend; added together this gives the percentage of the whole sample population that regarded the strategies as very
important or important (the remaining percentages refer to those who scored each option as either ‘neither significant or
insignificant’, ‘insignificant’, ‘very insignificant’ or ‘do not know’).
Significant differences between the four cities were assessed using a nonparametric
one-way ANOVA (Kruskal-Wallis Independent samples test). When these analyses indi-
cated significance (at the 0.05 level), a Dunn’s Post Hoc Non-Parametric Test, adjusted by
the Bonferroni correction for multiple tests, was used to determine which cities were sig-
nificantly different from each other.
5. Results
5.1. Water Challenges
Overall, three water challenges are jointly ranked highest for importance by the sam-
ple population (n = 64): fluvial flood risk; increasingly frequent extreme rainfall events;
and water quality deterioration and river health (median rankings, Figure 3). Median
rankings in the four cities differ. Both Newcastle and Portland respondents regard age-
ing/outdated water and wastewater infrastructure as the highest-ranking challenge, likely
due to the (historic and current) prevalence of Combined Sewer Overflows (CSOs) and
flooding caused by old combined sewer systems. The highest ranking challenge in Ningbo
is water quality deterioration and river health, and in Rotterdam, increasingly frequent
extreme rainfall events is ranked the highest (likely due to the strong public profile of
managing ‘cloudburst’ events [72]). As Rotterdam and Ningbo are delta cities, coastal
flooding and storm surges was perceived to be a key water challenges (median ranking of
2 and 4, respectively, where lower rankings denote greater importance of the challenge,
see Supplementary Table S1). Challenges relating to water scarcity (e.g., water supply,
drought risk and low groundwater levels) are ranked lower. No statistically significant
differences were observed between all four cities (Supplementary Table S1). Water chal-

Water 2021, 13, 544 13 of 25
lenges suggested in the free text response include pinch points in the infrastructure net-
work, low stream flows and high water temperatures, and extreme heat (Supplementary
Material).
5.2. Multiple Benefits of BGI
Two benefits (flood risk and stormwater management, and water quality improve-
ments) are regarded as very important or important by 97% of the sample population, and
by 100% of Portland respondents (Figure 4). Health and wellbeing improvements, en-
hanced biodiversity, increased attractiveness/aesthetics and improved sense of place are
deemed very important or important by more than 80% of respondents in each city. Ben-
efits that may not automatically be associated with BGI, such as noise reduction, provision
of jobs and increase in property prices, are regarded as less important (aside from Ningbo,
where 76% regard increases in property prices and noise reduction as very important or
important).
Several key differences between the cities are evident. Reducing urban heat is a key
benefit in Ningbo, perceived by 94% of respondents as very important or important (sta-
tistically significant difference observed between Ningbo and Newcastle, p = 0.033, Sup-
plementary Table S2), likely due to the different climate profiles, size and density of ur-
banisation in these two cities (the latter being much higher in Ningbo). The educational
and recreational opportunities of BGI are key benefits in Newcastle, regarded as very im-
portant or important by 100% of respondents (statistically significant difference observed
between Newcastle and Portland for recreational opportunities, p = 0.006). The carbon se-
questration potential of BGI is an important benefit for 100% of Portland respondents (sta-
tistically significant difference observed between Portland and Rotterdam, p = 0.001). Re-
spondents’ disciplinary backgrounds were not found to significantly influence the per-
ceptions of BGI benefits (Supplementary Table S3).
5.3. Drivers for BGI Implementation
Socio-political and instrumental drivers for BGI implementation differ between the
four cities and within each city group, evident by the number of drivers in Figure 5 that
attracted neither high nor low agreement in responses between stakeholders (shaded yel-
low). There is, however, a general consensus that local government plans are more effec-
tive drivers than national government legislation in all cities, although the difference be-
tween respondents regarding local government plans as an effective driver of BGI (94%)
and respondents regarding national government legislation as an effective driver (88%) is
much smaller in Ningbo compared with the other cities. In contrast, no Rotterdam re-
spondents regard national government legislation as an effective driver (statistically sig-
nificantly different from the other cities (p = 0.000, Supplementary Table S4)). While the
Dutch National Government may provide overarching principles for urban water man-
agement, BGI strategies are driven by local and municipal authorities.
A total of 88% of Newcastle respondents perceive multi-agency approaches as an
effective driver, compared with 35% in Ningbo (statistically significantly different; p =
0.013). In Portland, 80% view the recognition of BGI multifunctionality, and quantification
and monetisation of the benefits and costs, as effective drivers, likely due to long-standing
methods of calculating the multiple benefits of BGI [73]. Aside from Newcastle (63%), lo-
cal flood authority guidance was selected by less than 50% of respondents. The role of
lobbying from local communities, e.g., for agencies/organisations to act to reduce flood
risk, is regarded as a more effective driver in Newcastle (50%) compared with Portland
(40%), Rotterdam (19%) and Ningbo (12%). Other effective factors for driving BGI imple-
mentation were identified in the free text response, including commitment from the com-
munity (Portland), catchment plans (Newcastle), local design, construction and mainte-
nance guidance (Portland) and “courage to deviate / to think freely” (Rotterdam, R5; Sup-
plementary Material).

Water 2021, 13, 544 14 of 25
5.4. BGI Leaders
There is a marked difference in perceptions of who is currently leading BGI imple-
mentation in the four cities, and who should take the lead on initiatives (Figure 6). A total
of 84% of all respondents perceive local government as BGI leaders (Figure 6e) (94% in
Ningbo, Figure 6b). In contrast, only 50% believe that local government should lead, com-
pared with 56% who think that developers should lead (Figure 6e) (100% in Newcastle,
Figure 6a). Statistically significant differences are evident between cities. Private water
and sewerage companies are perceived to lead BGI implementation in Newcastle signifi-
cantly more than in Ningbo (p = 0.000), Portland (p = 0.000), and Rotterdam (p = 0.000)
(Supplementary Table S5). Nonprofits are perceived to lead BGI implementation in Port-
land significantly more than in Newcastle (p = 0.005), Ningbo (p = 0.000), and Rotterdam
(p = 0.000). Communities in Rotterdam and Portland are perceived to lead the way signif-
icantly more than communities in Newcastle and Ningbo (p = 0.000). No significant dif-
ferences were observed when asking who should lead BGI implementation (Supplemen-
tary Table S6).
Several other options were presented in the free text responses including housing
corporations (Rotterdam), Ministry of Housing and Construction Bureau (Ningbo) and
landowners, land agents and surveyors (Newcastle; Supplementary Material ), which sug-
gests a leadership role should be played by these organisations in BGI delivery in new
development. One respondent from Newcastle remarked that “no one organisation is lead-
ing the way—it is more via partnerships leading” (NE24), highlighting the importance of
multi-agency partnerships in BGI implementation in Newcastle (which was also regarded
as an effective driver by 88% of Newcastle respondents, Section 5.3). The low response
rate of Ningbo respondents regarding who should lead (only 76% recorded a response
and most only selected one option) suggests a different interpretation of this question than
in the other cities where multiple options were selected by each respondent.
5.5. Overcoming Barriers to BGI Implementation
Overall, there is strong agreement within and between the cities that most of the 19
options suggested as ways to improve the uptake of BGI are very important or important,
and therefore key to overcoming the barriers to widespread BGI implementation (Figure
7). Four changes to current systems of BGI implementation are perceived by over 90% of
the sample population as essential for improving BGI uptake; increased awareness (pol-
icy-makers) (94%), wider range of funding (94%), BGI in new developments (92%), and
increased funding for BGI (91%). We interpret ‘wider range of funding’ as an increase in
the range of funding sources for BGI projects, e.g., public, private and nonprofit organisa-
tions, whereas ‘increased funding for BGI’ implies a net increase in funds designated to
BGI projects which could potentially stem from one source. While this was not specified
to the survey respondents, the fact that both options related to funding were selected by
over 90% of the sample population suggests that current funding mechanisms are insuf-
ficient to deliver BGI aspirations. In contrast, stronger national legislation is deemed very
important or important by 68% of the sample population (although the low percentage
agreement in Rotterdam (20%) reduces the overall value).
Differences are evident between the four cities. For example, 100% of Newcastle re-
spondents perceive changes in cultures and behaviours as very important or important,
compared with 71% in Ningbo, 87% in Portland, and 73% in Rotterdam. This likely stems
from a perceived reluctance to support “novel” approaches and change practices around
flood and water management that [39] reported in an earlier study. Clearer maintenance
responsibilities are viewed as very important or important by 100% of Ningbo respond-
ents, compared with 88% in Newcastle, 73% in Portland, and 94% in Rotterdam.
Rotterdam has the most unique perception of the strategies to improve the uptake of
BGI, and in particular, the limited role of ‘command and control’ governance. For instance,

Water 2021, 13, 544 15 of 25
only 20% of respondents perceive stronger national legislation as very important or im-
portant (statistically significant difference to responses in Newcastle (p = 0.000), Ningbo
(p = 0.000) and Portland (p = 0.001), Supplementary Table S7). Stronger enforcement from
the planning system (33%) and mandatory standards (50%) are also regarded as very im-
portant or important by less than half of Rotterdam respondents (statistically significant
differences between respondents from Rotterdam and the three other cities were observed
and are detailed in Supplementary Table S7). Enforcement, particularly at the national
level, is likely to be less effective in Rotterdam where BGI implementation is driven by
local and municipal authorities.
6. Discussion
This study investigates the perceptions of BGI held by professional stakeholders in
four international cities with established BGI programs and visions for a future where
combined systems of blue, green and grey infrastructure are employed to address urban
water challenges. This study builds on earlier evaluations and comparisons of the percep-
tions of sustainable stormwater management and BGI in international cities [20,47,48],
bringing a wider range of disciplines to the discussion by including responses from engi-
neers, environmental managers, designers, planners, and those involved in BGI strategy,
policy, finance and implementation (albeit limited to 64 responses, see Section 4.1.1. for
discussion of the small sample size). Insight into general BGI best practices from the four
surveyed cities, and specific approaches of individual cities, are now discussed in the con-
text of (1) using BGI to deliver multiple benefits, and (2) governance and leadership that
facilitate widespread implementation of multifunctional BGI.
6.1. Delivery of Multiple Benefits by Multifunctional BGI
In all four cities, BGI is acknowledged as providing a range of benefits that can be
categorised as biophysical (e.g., urban water cycle and environmental management); so-
cial (e.g., health and wellbeing); and economic (e.g., increased property prices). However,
the most important benefits (flood risk and stormwater management, and water quality
improvement) suggests that, despite the increasing international focus on BGI as multi-
functional infrastructure [9,12,31,32,34], it is primarily perceived as infrastructure to man-
age water cycle processes. Nonetheless, agreement by the majority of the sample popula-
tion that BGI improves health, wellbeing and sense of place, enhances biodiversity, and
increases attractiveness of urban environments, suggests that benefit provision outside of
the hydrosphere is still highly important.
The perception of multiple benefit delivery is a key component of current water man-
agement strategies in Newcastle [52], Ningbo [53], Portland [54] and Rotterdam [56]. Such
approaches emphasise a move away from the traditional reliance on grey infrastructure
to manage urban water, and greater support for approaches that concurrently address key
social, environmental, and economic challenges [20,21]. A leading theme in all cities, and
exemplified in Rotterdam, is the use of BGI to improve the quality of life [62]. Perceptions
of the important benefits of BGI noted by respondents in each city are supported by local
and national practices and policies, which could be regarded as exemplars for other cities
looking to better incorporate multifunctional BGI into their own urban improvement
strategies.
In the UK, the ‘four pillars of SuDS (sustainable drainage system) design’, comprising
water quantity, water quality, amenity and biodiversity objectives [74], support many BGI
systems, explaining why these benefits are regarded as very important or important by
over 90% of Newcastle respondents. Urban water and extreme weather event manage-
ment is only one intended outcome of Rotterdam’s climate resilience strategies. The cur-
rent edition of Rotterdam’s Waterplan, Rotterdam Weather-Wise, highlights the opportuni-
ties offered by physical adaptation of the city to mitigate impacts of climate change, pri-
marily the creation of more attractive public green spaces and blue corridors that will im-

Water 2021, 13, 544 16 of 25
prove water and air quality, enhance biodiversity and improve the cityscape [72]. In Port-
land, BGI has typically been implemented to improve water quality, manage nuisance
flood risk, and reduce loadings on the piped infrastructure system [58], explaining why
100% of respondents regard these benefits as very important or important. Carbon seques-
tration, also regarded as very important or important by all Portland respondents, is a key
component of the Climate Action Plan and county-wide initiatives to improve natural
systems and increase urban forests [75]. The key objectives of the Chinese SCP focus on
water cycle and flood risk management, and improvement of the natural environment
through better alignment between urban planning and water resource management [53].
Greater implementation of BGI in urban areas and conservation of existing blue and green
spaces are also proposed to improve social wellbeing [68], explaining the benefits that the
Ningbo participants regarded as very important or important.
The benefits of BGI that were identified as most important also align with the highest-
ranking water challenges (fluvial flood risk, increasingly frequent extreme rainfall events,
and water quality deterioration and river health). Unsurprisingly, the city objectives for
more sustainable and resilient future water management mirror the city-specific water
challenges illustrated in Figure 3. At present, risks associated with having too much water
are driving urban water management agendas. The challenges related to having too little
water (water supply, drought risk and low groundwater levels) have less dominance in
decision making as that current risk is perceived to be low. Nonetheless, the potential for
BGI to mitigate future risks of water scarcity is acknowledged by survey respondents and
illustrated by the relatively high percentages who regard rainwater use, e.g., via rainwater
harvesting, as a very important or important BGI benefit.
6.2. Overcoming Barriers through BGI Leadership and Governance
The perceptions of governance drivers for BGI implementation, BGI leaders, and
strategies to overcome the barriers and improve BGI uptake, are markedly different be-
tween the four cities, reflecting the varied local, regional and national responsibilities for
BGI implementation, and urban water management policy more generally.
6.2.1. National and Local Government Leadership
One theme that is apparent is the key role national governments are perceived to play
in both leading and driving BGI implementation in Ningbo. The Chinese National Gov-
ernment, which has responsibility for stormwater management in China, is a key driver
of BGI implementation and has provided funding for the thirty pilot Sponge Cities [53].
In the hierarchical Chinese governance system, the national government is responsible for
developing mandatory standards and clearer maintenance responsibilities to enable bar-
riers to BGI to be overcome (Figure 7). Interestingly, local government plans are perceived
by a greater percentage of Ningbo respondents (94%) as drivers of BGI implementation
(compared with 88% who selected the National Government, Figure 5). This may reflect
the overarching role that national policy has in setting local government priorities in Chi-
nese cities but the need for local government to implement strategies on the ground by
coordinating and monitoring the work of city bureaus [47]. This aligns with the perception
that the local government is Ningbo’s BGI leader (94% agreement). As respondent N29
noted:
“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.”
In contrast, policies that govern BGI in Rotterdam, primarily as part of wider urban
water management and climate change adaptation strategies, including the Rotterdam
Resilience Strategy [76]and Rotterdam Weather-Wise [72], are driven by local and munic-
ipal authorities. The Dutch National Water Plan (2016–2021) provides overarching princi-
ples and direction of national water policy over five year planning cycles [56], which are

Water 2021, 13, 544 17 of 25
then adapted and detailed for specific regions by local and municipal governments. This
explains why no Rotterdam respondents perceived national government legislation as a
driver for BGI, and only 20% regarded stronger national legislation as a very important
or important strategy to improve BGI uptake (Figure 7). Mandatory standards and
stronger enforcement from the planning system are also not deemed as important; the
Dutch National Government does not typically provide mandatory standards, instead is-
suing planning guidance and recommended approaches, e.g., Delta Plan on Spatial Adap-
tation [77]. Clear links between climate change adaptation projects and spatial planning
already exist [17,56] and there is a strong focus on delivery [72]. While the development
of adaptation strategies is mandatory for local and regional governments, the incorpora-
tion of BGI is encouraged but is not mandatory. On one hand, this provides local and
regional governments with greater freedom to develop their adaptation measures, yet
there is a risk that single purpose grey infrastructure systems will remain a favoured ap-
proach. The annual investment budget to maintain urban drainage in Rotterdam is 14.2
million Euros, yet only 10% of this budget is allowed to be invested in sustainable and
multifunctional drainage solutions like BGI [78].
The importance of local government plans in driving BGI uptake is evident in all
cities (Figure 5) and mirrored in the perceptions of current leaders of BGI implementation
(84% selected local government, Figure 6). In Newcastle, three organisations are perceived
as BGI leaders, reflecting the partnership between Newcastle City Council, the Environ-
ment Agency and Northumbrian Water (private water and sewerage company) that is
evident on many BGI projects [39,52]. These organisations, and others, also helped found
the 2019 Newcastle Declaration on Blue and Green Infrastructure that advocates changing
working practices towards greater collaboration and mechanisms to realise the multiple
benefits of BGI [79]. Multi-agency partnerships are the cornerstone of current BGI projects
in Newcastle, as in many UK cities, as advocated in policy and practice, e.g., in the New-
castle City Strategic Surface Water Management Plan [52]. This explains why 88% of New-
castle respondents perceived multi-agency approaches as a driver of BGI implementation
(Figure 5).
The approach in Portland is different, as individual cities and counties are advancing
their own approach to BGI, with some support from Federal agencies. In a study of green
stormwater infrastructure in three US cities (including Portland), [58] observed that fed-
eral regulations did not appear to exert as strong of an influence on BGI as is typically
presumed. This trend is echoed in the data presented here; only 47% regarded national
government legislation as a very important or important driver of BGI implementation
(Figure 5). Instead, the recognition of multifunctionality, and quantifying and monetising
the benefits and costs of BGI, presumably to help make the case for multifunctional infra-
structure to a range of potential funders, are regarded as more significant drivers of BGI.
6.2.2. Nonprofits and Citizen Advocacy
A trio of organisations are perceived as leading BGI adoption in Portland: communi-
ties, nonprofits and individual champions (Figure 6). Individual champions may be part
of local government organisations, such as the Bureau of Environmental Services (BES),
which manages Portland′s wastewater and stormwater infrastructure. This bottom-up,
‘grassroots’ approach, involving both public and private actors, stems from a lawsuit filed
in 1991 by Northwest Environmental Advocates (NWEA) against the city of Portland al-
leging that regular discharges of untreated effluent (CSOs) violated the Clean Water Act.
Shortly after the lawsuit was filed, Oregon’s Department of Environmental Quality (DEQ)
ordered the city to reduce CSO discharges using its authority under the Clean Water Act.
NWEA’s litigation resulted in a consent decree that the city of Portland obey DEQ’s order
to reduce CSOs [80]. This lawsuit established “a national legal precedent that citizens can
enforce narrative conditions in water pollution discharge permits.” [81].

Water 2021, 13, 544 18 of 25
Citizen advocacy is long-standing in Portland; indeed, the city was one of the first to
advocate for green stormwater solutions to address combined sewer overflow (CSO) reg-
ulations, which was led by an involved citizen advisory panel [21]. A range of nonprofits,
public and private organisations, often led by individual champions, are dedicated to con-
serving existing blue-green space and wildlife, improving watershed health, ensuring that
greenspace is accessible to everyone, and petitioning for the equitable delivery of BGI in
urban neighbourhoods. Portland, more so than the other cities, demonstrates the im-
portance of citizen advocacy, led by informed, knowledgeable citizens with access to in-
formation on urban BGI, in raising the profile of BGI and enabling widespread delivery
of BGI systems.
The role of the community in BGI implementation is most apparent in Rotterdam;
the joint leaders of BGI are perceived to be local government and the community
(Figure 6). Rotterdam communities play a key role in decision making around climate
change adaptation and resilience, and are involved throughout the lifetime of projects.
For example, the Benthemplein water square, which provides water storage during rain-
fall events while concurrently improving the quality of urban public space, involved a
wide range of community groups in the design and planning phase. This included teach-
ers and students at the local college, faith groups and local residents, to ensure that the
final design offered activities in neighbourhood spaces that were most desired by local
stakeholders, in addition to managing rainfall [82]. A move away from top-down hierar-
chy towards greater levels of community and citizen involvement are also key compo-
nents of the Rotterdam Resilience Strategy [76]. In contrast, communities do not take such
a leading role in Ningbo (perceived by 6% as leading BGI), as citizens are typically in-
formed about SCP projects, with limited engagement and consultation [47], which again
stems back to the hierarchical governance structure.
It is interesting to note that the organisations currently perceived as BGI leaders in
Newcastle and Portland are different from the organisations that respondents say should
be leading BGI (Figure 6). All Newcastle respondents believed that developers should be
leading BGI, likely due to the housing delivery targets of Newcastle City Council over the
next few decades and the focus on high quality sustainable drainage to manage water and
flood risk on site [63]. In Portland, greater leadership on BGI is thought to be needed from
the U.S. Environmental Protection Agency (EPA), which is the federal agency in charge of
administering the Clean Water Act. EPA encourages the use of green infrastructure to
manage “wet weather” and, since 2007, EPA’s Office of Water has released memos detail-
ing how green infrastructure can be integrated into federal regulatory programs [83].
6.2.3. Improving Uptake of BGI
Despite the four case study cities having strong BGI visions and aspirations, more
than 50% of the respondents from each city still perceive all options for improving BGI
uptake as very important or important (Figure 7). This highlights the myriad barriers to
BGI delivery that are still hampering progress [35,36], and the need for concurrent change
in cognitive, normative and regulative conditions of urban water management [20]. It fur-
ther suggests that the changes needed to improve BGI uptake, as outlined in Section 5.5,
have international relevance for other cities on their journeys to sustainable urban water
management and blue-green futures. This includes increasing the awareness of policy-
makers to the multifunctional benefits of BGI that may meet different city objectives if
designed with more than water management in mind. A wider range of funding, and in-
creased funding for BGI, were very important in all cities suggesting that despite the grad-
ual transformation from solely grey to combinations of blue, green and grey infrastruc-
ture, and changes in attitudes towards BGI, greater monetary support is still needed if
cities are to meet their blue-green aspirations. Other drivers, such as building codes and
rating systems, are also important for BGI implementation [49].
6.3. Key Insights

Water 2021, 13, 544 19 of 25
This research provides three key insights that have relevance for other cities inter-
ested in investing in BGI and progressing with their journeys to a sustainable blue-green
future. First, the international acknowledgement of the multiple environmental, social
and economic benefits delivered by BGI suggests a need for transformation in policy and
practice towards greater implementation of BGI that is truly multifunctional, rather than
being designed to specifically manage water and flood risk and only paying lip service to
wider benefit provision. While BGI cannot be designed to deliver all possible benefits sim-
ultaneously, improving quality of life through high quality BGI is likely to be high on the
political agendas of many cities. The geographical, climatological, socio-political and gov-
ernance characteristics of cities will influence local BGI design, guided by the priorities
and strategic objectives of each city, and negotiated by the stakeholders involved in BGI
projects to maximise benefits and determine which benefit trade-offs will be made (e.g.,
see [84] for a discussion of conflicts between minimising flood and heat risks in cities).
Second, in cities with non-hierarchical governance structures, the national govern-
ment plays a pivotal role in setting overarching criteria for managing urban water man-
agement and addressing environmental challenges. However, local governments typi-
cally drive BGI projects in line with their strategic objectives. Multi-agency approaches
are becoming increasingly common and such collaborative approaches, particularly if
they include nonprofits and community groups, are increasingly likely to deliver BGI that
is understood and supported by decision makers and local communities. Cities looking to
expand their BGI delivery are recommended to develop partnerships and multi-agency
approaches, facilitated by frameworks that bring together disparate stakeholders to nego-
tiate innovative solutions to specific challenges, such as Learning and Action Alliances
that enable social learning, knowledge transfer and collaboration [85,86].
Finally, there is no one solution to overcoming the barriers to BGI owing to the range
of biophysical and socio-political barriers that hamper progress, and the intersectional na-
ture of the challenges [36,37]. Cities and countries also have differing abilities to support
strategies to overcome the barriers (e.g., changes in national legislation may not univer-
sally be a suitable option). Concerted effort should be made to reduce some of the bio-
physical uncertainties through better data and improved scientific understanding along-
side investment in education, partnership working and funding for both capital works
and ongoing maintenance of BGI (see also [36]). While outside the scope of this study,
cities interested in investing in BGI are also encouraged to explore innovative funding for
BGI schemes where traditional governmental routes may not be possible, as combinations
of funding have resulted in successful projects, e.g., Rebuild by Design in Hoboken, New
York, funded by the federal government and private sector funding [87].
6.4. Limitations of the Survey
The conclusions drawn from this cross-country comparison of the perceptions of BGI
have general applicability outside of the sampling frame, e.g., most significant BGI bene-
fits, role of local government, and strategies to improve the uptake of BGI. However, the
geographically targeted nature of this investigation precludes direct applicability of the
data presented in this study with other cities due to the strong influence of local context
(geographical, climatological, socio-political and governance characteristics); instead, we
recommend that similar surveys be undertaken with a range of stakeholders involved in
BGI in other cities, to improve understanding of BGI attitudes across the globe. Percep-
tions may also be influenced by many other factors that were not controlled for in this
study, including demographics, broader environmental attitudes, and performance of
practices associated with urban BGI that are undertaken by the respondents (e.g., dog
walking, exercising, recreation), which [70] propose transcend locational and demo-
graphic factors.
The sampling frame was limited to existing contacts of the project team and does not
include representation of all disciplines and organisations involved in BGI. As an exam-

Water 2021, 13, 544 20 of 25
ple, health professionals were not surveyed despite the growing importance and acknowl-
edgement of the physical and mental health benefits of BGI [12]. The small percentage of
planners that completed the questionnaire was also disappointing, as in many cities plan-
ners are key players in BGI provision [88]. The nature of online surveys means it is difficult
to control who will and will not respond; hence, better representation by these groups
may have influenced the trends for each city, although respondents’ disciplinary back-
grounds were not found to significantly influence the perceptions of BGI benefits (Sup-
plementary Table S3).
With regard to the survey, the predefined responses in the categorical and multiple
choice questions may not have adequately captured all respondents’ perceptions, alt-
hough this was mitigated somewhat by providing space for ‘other’ responses. Finally, it
is possible that some of the survey questions, originally drafted in English, were not in-
terpreted as intended after translation into Chinese or Dutch, which might explain the low
response rate of Ningbo respondents regarding who should lead BGI implementation
(only 76% recorded a response and most only selected one option, rather than ‘all options
that apply’).
7. Conclusions
This research presents detailed contextualised knowledge of the perceptions of BGI
drivers, leadership, multiple benefits, and strategies to overcome barriers to widespread
implementation, in four international cities with established BGI programs: Newcastle
(UK), Ningbo (China), Portland (Oregon USA), and Rotterdam (Netherlands). Comparing
BGI perceptions in the four cities has further created a nuanced understanding of how the
geographical, climatological, socio-political and governance similarities and differences
between these cities influence perceptions towards BGI, and its role in urban water and
environmental management. Perceptions of the water challenges and benefits of BGI are
influenced by the geographical and climatological features of each city; all cities are situ-
ated along rivers which has raised awareness of fluvial flood risk and declining river
health while Ningbo and Rotterdam are delta cities with increased perceived risk of
coastal flooding and storm surges. Socio-political factors, governance and population dy-
namics has influenced perceptions of the socio-political drivers for BGI implementation,
BGI leaders and how barriers to BGI may be overcome, and the influence of ‘command
and control’ governance in Ningbo has illustrated marked differences between the per-
ceptions of Ningbo stakeholders and those in the other three cities.
While BGI is primarily used to manage too much water (e.g., pluvial and fluvial flood
risk), there is strong support for designing BGI to deliver social and environmental bene-
fits, illustrating the growing international trend for BGI as a mechanism to improve qual-
ity of life i n urba n environme nts and beco me more than a strat egy to manag e wate r. None -
theless, a transformative change in policy and practice towards truly multifunctional in-
frastructure is needed to optimise the delivery of multiple BGI benefits that address pri-
orities and strategic objectives of cities. The multiple benefits perceived as provided by
BGI attest to the need to understand a broad range of stakeholder perspectives to deter-
mine how BGI may meet the strategic objectives of different organisation and depart-
ments, and particularly those that lie outside of the flood and water management domain.
One way to increase the breadth of stakeholder involvement in BGI projects is to foster
greater levels of community and citizen involvement, as illustrated in Portland and Rot-
terdam with their move away from top-down hierarchical decision making towards
‘grassroots’ and community leadership.
The myriad barriers to BGI that hamper progress means that no one solution can
hope to overcome the range of biophysical and socio-political challenges. However, better
data and improved scientific understanding can help reduce biophysical uncertainties,
while investment in awareness raising, greater partnership working and funding (ideally
from a wider range of sources) for both capital works and ongoing maintenance of BGI
may improve the uptake of BGI. New development has the potential to play a key role in

Water 2021, 13, 544 21 of 25
delivering high quality BGI if BGI is a cornerstone of the development proposal, consid-
ered at the outset of the planning process and multifunctionality is a core component.
Supplementary Materials: The following are available online at www.mdpi.com/2073-
4441/13/4/544/s1, detailed information on the case study cities, a copy of the survey questions and
responses to the free text option in questions 1, 3–4. Figure S1: Survey home page with language
selection box, Table S1: Ranking of the water challenges identified by the whole sample population
and for each case study city, Table S2: Percentages of respondents in the whole sample population
and each city that regarded the benefits of Blue-Green infrastructure (BGI) as very important or
important, Table S3: Testing for statistically significant differences between respondents’ discipli-
nary backgrounds and perceptions of the very important benefits of BGI, Table S4: Effective socio-
political and instrumental drivers for implementation of BGI in the four cities, Table S5: Perceptions
of who are leading the way in BGI implementation in the case study cities, Table S6: Perceptions of
who should lead the way in BGI implementation in the case study cities, Table S7: The percentages
of respondents from each city that regard different strategies for improving the uptake of BGI as
very important or important.
Author Contributions: Conceptualisation, all authors; data curation, E.C.O.; formal analysis,
E.C.O.; funding acquisition, S.N.G. and E.C.O.; methodology, E.C.O and N.R.N.; writing–original
draft, E.C.O. and N.R.N.; Writing–review & editing, F.K.S.C., N.J.D. and S.N.G. All authors have
read and agreed to the published version of the manuscript.
Funding: This research was performed as part of the British Academy project ‘Developing new
Blue-Green futures: multifunctional infrastructure to address water challenges’, part of the British
Academy programme on Tackling the UK’s International Challenges (grant reference
IC3\100093). Additional funding provided by Reed College and the Bernard Goldhammer Grant
for Research on Economics and Natural Resources at Reed College.
Institutional Review Board Statement: The study was conducted according to the guidelines of the
Declaration of Helsinki, and approved by the Ethics Committee of the University of Nottingham (4
March 2019).”
Informed Consent Statement: Informed consent was obtained from all subjects involved in the
study.
Data Availability Statement: Data sharing, such as individual responses to the survey questions, is
not applicable to this study due to its confidential nature.
Acknowledgments: We would like to express our thanks to all respondents who gave their time
to complete the survey and to Will Daniel and Lei Li who assisted with the Qualtrics survey.
Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the
design of the study; in the collection, analyses, or interpretation of data; in the writing of the man-
uscript, or in the decision to publish the results.
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