Key takeaways
- Since 2013, sponge city construction
is promoted as a national climate adaptation strategy in China. Implementation
started with the designation of 30 national-level pilot cities in 2015 and 2016.
It was then expanded to cities and urban areas across the country and at the
provincial level.
- The sponge city is not a single
storm water management instrument. Rather, it is intended to draw from a
portfolio of measures and strategies that are often characterised as
environment-oriented, multi-functional and low-tech. This shall reduce costs as
compared to former approaches merely relying on grey infrastructure.
- The sponge city combines individual
adaptation measures and technologies developed and promoted internationally
under designations such as low-impact development (United States), sustainable
urban drainage systems (United Kingdom), blue-green infrastructure (other European
countries) and water sensitive urban design (Australia).
- While sponge city measures such as
the construction of wetland parks greatly increase liveability in densely
populated urban areas, such interventions may raise real estate prices in
surrounding residential districts and spur gentrification.
- The main challenges in
implementation are administrative and political, e.g. lack of consultation and
cooperation across departmental and (sometimes) municipal boundaries.
- In cities with completed sponge city
facilities where flooding occurred nonetheless, problems were often traced back
to deficiencies in construction and spot-level rather than comprehensive
development.
Introduction
In July 2021, extreme precipitation
caused catastrophic flooding in Zhengzhou, the capital of China’s Henan
Province, which aspires to become a so-called “sponge city” (haimian
chengshi 海绵城市). According to official figures, 380 people lost their lives within
the city area, and the overall economic loss of the disaster reached RMB 40,9
billion (approx. EUR 5,2 billion). Although extreme weather events are not
uncommon in China, especially during the summer months, the Zhengzhou floods received
high domestic and international attention. In addition to the question of how
local authorities dealt with the disaster, discussions arose about the
effectiveness of China’s sponge cities. This urban development approach is ecosystem-based
and aims at responding to extreme weather – a threat that has been projected to
occur more frequently worldwide in the future.
The transformation of cities towards
climate-resilience is a global challenge that requires EU-China cooperation.
While sponge city construction in China (nationwide initiative) and urban
climate adaptation in many EU countries (more decentralised measures) differ in
their overall approach, both strive to foster nature-based and low-tech
solutions. Wider exchange of knowledge and implementation experiences will
allow for a stronger consideration of distinctive local conditions
(hydrological, climatic, socioeconomic) rather than “one-size-fits-all” modelling.
Moreover, exchange has been and is expected to be beneficial with regard to
setting up financing and evaluation schemes for climate adaptation measures. Besides
the mitigation of disaster risks, sponge cities strive to conserve urban
biodiversity and improve city dwellers’ well-being and health. These factors
are becoming more important to gain public support for climate adaptation in both
China and Europe.
What does “sponge city” mean in a
Chinese context?
Sponge cities are mostly known for addressing
two seemingly contradictory urban threats amplified by global climatic changes:
flooding and water shortages. The basic urban planning concept behind this
ostensive metaphor, which is said to have originated in China, is to render the
city “absorbent as a sponge”. By use of flooding areas, wetlands, and
nature-based technologies such as bioretention swales (vegetated and landscaped
depressions with gently sloping sides designed to filter pollutants and
temporarily capture rainwater), storm water shall be stored where it falls instead
of being drained directly via networks of pipes and sewers. In turn, during
hotter weather, water evaporating from these areas is expected to reduce heat
effects. Moreover, well thought-out interventions are multifunctional, making full
use of their potential to improve liveability in the city, e.g. by increasing green
spaces that enhance air and aesthetic qualities. Their mostly nature-based and
low-tech strategies often require a lower budget than conventional grey
infrastructure solutions.
Ecological measures to manage storm
water, purify precipitation runoff and reduce heat and flooding risks of
cemented and asphalted surfaces in urban centres have been developed worldwide
since around the 1980s. These include best management practices (BMPs) and
low-impact development (LID) in the United States, sustainable urban drainage
systems (SuDS) in the United Kingdom, water sensitive urban design (WSUD) in
Australia and blue-green infrastructure in many countries of continental Europe.
The Chinese sponge city draws on individual technologies and measures from
these schemes, but is conceptualised as holistic approach. Chinese landscape
architect Yu Kongjian, Dean of the College of Architecture and Landscape
Architecture at Peking University, is credited as founder of the sponge city
concept and, most importantly, for having achieved buy-in from the central
government. In the long term, he and his architectural firm “Turenscape” envision
the establishment of a nationwide ecological security
system based
on spatial analysis of hydrological processes at the macro scale (regional and national).
How effective are sponge cities for
climate change adaptation?
In contrast to Europe where green
transformations of urban centres are usually done at the initiative of
pioneering municipalities, sponge city construction is promoted on a nationwide
scale in China since the mid-2010s. A key event that catapulted stormwater
management onto the national agenda was a disaster in 2012, the Beijing floods,
in which 79 people lost their lives. Only three years later, the State Council
issued its Guidelines for the Promotion of
Sponge City Construction that define a very ambitious goal: 70% of precipitation shall be
collected, stored and utilised where it falls, a target which is to be achieved
for more than 80% of built-up areas in Chinese cities by 2030. Practical
implementation started with the designation of 16 pilot cities and areas in
2015 and another 14 cities in a second batch one year later. Systematic
nationwide rollout began in 2021 and by now encompasses 60 so-called “model
cities” that were selected in three rounds. The budget these model cities
receive varies according to administrative level and geographical location. In
the second batch, prefecture-level cities and above
received RMB 900 million (approx. EUR 115 million) of subsidies in the eastern
region, RMB 1 billion (approx. EUR 128 million) in the central region and RMB
1.1 billion (approx. EUR 140 million) in the less developed western region of
the country. County-level cities were provided RMB 700 million (approx. EUR 90
million) in the eastern, RMB 800 million (approx. EUR 102 million) in the
central and RMB 900 million (approx. EUR 115 million) in the western regions.
The subsidies are allocated over a three-year period in accordance with the
progress of implementation.
In China, the effectiveness of
sponge cities was first questioned in 2016, shortly after the usual annual
flooding period. By then, ten pilot cities from the first, and nine from the
second batch had again been affected by flooding or waterlogging. Authorities
defended the approach by pointing to the short period of time since the programme’s
implementation and to its still ongoing construction. In this context, the
aspect of disaster severity came into focus, leading cities to adapt their
drainage designs to larger return period events (from 1-in-1 and 1-in-5-year events
to 1-in-30-year events).
Record-breaking disasters such as
the Zhengzhou floods in 2021 further fuelled criticism against the sponge city
approach, given that the municipality had invested more than US$ 80 million (approx. EUR 73 million) over the
previous five years in green areas and infrastructure supposed to mitigate
flooding in Henan’s provincial capital of 12 million inhabitants. Yu Kongjian
defended the concept in an interview by the American Society of
Landscape Architects, saying that Zhengzhou could not yet be considered a
sponge city at the time of the disaster as the proportion of grey
infrastructure in the city was still far too high. He further pointed out the
problem that municipalities in China would sometimes simply use the term
“sponge city” for other types of interventions to obtain central government
funding.
Another point of criticism has been
the centralised character and universal application of guidelines, standards,
and evaluation criteria for sponge cities defined by national and regional
governments which do not always take full account of local problems caused by distinctive
climatic, hydrological and socioeconomic conditions. The regulation of sponge city
transformation is within the responsibility of three state authorities, the
Ministry of Housing and Urban-Rural Development (MOHURD), the Ministry of Water
Resources and the Ministry of Finance. Sponge city measures as defined by the
State Council encompass six categories:
- “infiltration”
(e.g. construction of green roofs and permeable pavements),
- “retention” (e.g. through sunken
green spaces),
- “storage” (e.g. preservation and
restoration of water bodies and wetlands),
- “purification” (e.g. construction of
water treatment plants),
- “utilisation” (e.g. through water
regeneration), and
- “drainage” (e.g. upgrade of sewer
systems).
Although an adaptation to local
conditions is explicitly stated as a basic principle in the Technical Guidelines issued by
MOHURD in
2014, this principle reaches its limits in practical implementation.
Do common global challenges provide
opportunities for cooperation?
In recent years, Europe also
experienced increasing weather extremes. In 2023, precipitation reached a
value of 7% above the annual average. Across almost the whole region,
above-average temperatures generated an increase of days with “strong” up to “extreme
heat stress”. Around 1.6 million people suffered from flooding and related
consequences, including 44 deaths. Moreover, weather and climate-related events
caused 81% of the total financial losses of EUR 13.4 billion.
In Europe, pioneering cities, such
as Vienna, Copenhagen, Amsterdam, Berlin, Hamburg and Leipzig play an important
role for developing and implementing climate adaptation measures. Copenhagen,
for example, builds on a dual approach where water is retained in basins
underground and green spaces above ground. Sealed surfaces are rendered
permeable and green roofs are constructed on new buildings in order to store
precipitation. In Groningen in the Netherlands, the nature-based transformation of Damsterplein
Square has
been a first initiative to increase the city’s overall climate-adaptation
capacity. The project further aims to involve residents, allowing them to plant
and maintain green spaces. Such strategies to increase public participation and
stakeholder involvement still constitute a deficiency in the sponge city
planning process and may therefore be a suitable starting point for
cooperation.
By continuously testing and
improving its sponge city strategies, China strives to become a global pioneer
and export domestic climate adaptation
solutions,
for example to developing partner countries in the Belt and Road Initiative.
This may prospectively position China in a competitive relationship with the
United States and EU member states that engage in green transformation. At the
same time, the different political approaches and practical experiences in
Chinese and European cities offer far-reaching opportunities for joint
initiatives in the transformation towards climate-resilient cities. Great
potential lies in exchanges with regard to methods, tools, financing mechanisms
and evaluation models, as well as co-creation strategies.
A hurdle faced in Chinese and
European cities alike is political and public support. Successful
implementation of climate adaptation measures requires close cooperation,
negotiation and approval of different municipal departments. Denmark has a long
tradition of close collaboration between public and
private partners as well as across authorities and organisations, which has
proven effective in other sectors such as cycling, for example, and may provide
inspiration for both European and Chinese cities. At the same time,
implementation of sponge city measures in Chinese cities has shown the significance
of enhancing liveability and health to gain public approval, e.g. by means of green spaces
construction and air quality improvement. As a large part of such
transformations usually relies on public resources, the support of local citizens
is crucial.
Financing
climate adaptation strategies is another common issue. In Chinese cities, a
major problem is to raise enough funds to implement sponge city measures. Chan et al. estimated the
cost for a three-year sponge city pilot project at RMB 1.2 to 1.8 billion
(approx. EUR 153 to 230 million). Especially in cities of the interior
where municipal budgets are low, public goods such as water management
infrastructure lack prioritisation, despite their smaller cost compared with
development schemes. The Chinese approach therefore puts great emphasis on
public private partnerships (PPP). However, such partnerships are again realised
much easier in developed coastal cities such as Shenzhen which partly relied on
private investment from its tech and manufacturing
corporations. Smaller urban municipalities in Europe with limited resources are
facing similar problems and obstacles in attracting investment. Here, it has
been suggested to cluster activities for climate adaptation into larger
portfolios. Other alternative financing mechanisms include municipal-issued
green bonds, a measure still rarely applied, and grants to property owners willing
to install green infrastructure. A promising subsidy scheme to mitigate flooding and extreme
weather events through decentralised measures of residents and private
businesses was introduced in the city of Bratislava, Slovakia, in 2016.
Networks
such as Local Governments for Sustainability (ICLEI), C40
Cities and United Cities and Local Governments (UCLG) have long been important platforms for
international exchange on such climate change adaptation strategies.
Furthermore, there have been efforts to integrate nature-based solutions in Chinese
and European city development as part of joint programmes such as UrbanByNature or the Sino-German Urbanisation Partnership
Project. Building
on these experiences, it is desirable that a regular exchange on urban climate
adaptation strategies in Europe and China is maintained to sound out potential
for future interest-orientated cooperation, in particular, at the subnational
level.
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Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Research Executive Agency (REA). Neither the European Union nor the granting authority can be held responsible for them.
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