Designing Sponge Cities for multiple benefits: integrating nature-based solutions to create sustainable places

Climate change will intensify urban and global problems like flooding, bad water quality, summer heat episodes, air pollution and biodiversity reduction. In China and Europe, there are attempts to counteract theses negative trends by using nature-based solutions (NbS), which are positive for biodiversity, can help to alleviate the above-mentioned problems and in addition provide secondary benefits to humans like increased well-being and recreation possibilities. The project "Designing Sponge Cities for multiple benefits: integrating NBS to create sustainable places - through Innovation, Policy, Health and Environmental Research (DeSCIPHER)" used the idea of "Sponge Cities" where NbS are used to manage stormwater (precipitation running off from impervious surfaces) reduce water and air pollution, high temperatures and noise, and improve recreation and health opportunities. Due to the COVID-19 pandemics, the project did not lead to an as close collaboration between Norwegian, British and Chinese Researchers as originally foreseen. There was i.e. only one physical project meeting in UK, other travel plans had not been possible to realize. However, the involved researchers tried to cooperate as good as possible by digital means and replace activities, which required physical presence with digital means or by involving local partners. For Norwegian project activities, i.e. surveys and interviews, NIVA started therefore a new cooperation with Duke-Kunshan University and sub-contracted the NIVA China office to conduct field work. The DeSCIPHER project has over its whole project period (2019-2023) yielded some interesting insights: 1) The effectiveness of NbS interventions in solving urban challenges are highly location-, scale- and size-dependent. Benefits of NbS largely increase with the size of the NbS intervention although there might be upper boundaries e.g. public health benefits do not or only slowly increase, when a certain size of park area is reached. Most NbS benefits decrease with the distance to the NbS intervention, but with different decay functions. In cities where space is a valuable and highly contested commodity, city planners should think in a wider spatial context when planning NbS, considering also space outside the city boundaries. Especially larger NbS can through natural movements of water, air, animals and plants and through human transport of resources, waste and people unfold their effects at places away from the original NbS location. A local improvement of water quality through NbS, will i.e. have an effect also further downstream. To optimize NbS benefits in the urban context it is necessary to take these considerations into account. Multi-functional assessment tools to evaluate trade-offs and co-benefits of various types of Nature-Based Solutions are highly required, although difficult to develop. 2) Rainfall-runoff models and water quality models are useful tools to determine the effect of NbS for stormwater management and water quality in urban water bodies. With hydrological models set up in DeSCIPHER, it could be shown that the implementation of small NbS interventions (raingardens, green roofs, swales and infiltration increasing interventions) in flooding hotspots in an urban catchment in Oslo (Norway), can reduce both flooding depth and discharge. Another modelling tool developed in DeSCIPHER allowed to gain some insights in the performance of the NbS “riparian tree planting” on water quality. It showed that tree planting on a 10 km stretch can substantially improve water quality in sensitive summer conditions. Water quality was expressed by the indicators water temperature, chlorophyll-a (a proxy for algae growth) and dissolved oxygen. 3) An economic experiment (choice-experiment) revealed that respondents in China were willing to contribute to more greenspaces and NbS solutions in cities, when these solutions come with a reduction in flooding frequency and temperature reduction in hot summer times. Respondents were willing to contribute with money, volunteering time or by transforming their privately owned land into greenspaces or small-size NbS. The same study showed also that citizens are positive towards a bit wilder-looking greenspaces i.e. where vegetation grows up to knee-height instead of being short cut. However, they would not prefer to have hip-high vegetation. This implies that there is a potential for cities to let vegetation grow a bit higher, which is positive for biodiversity, but also to save money by reducing maintenance intervals for greenspaces. It remains to be tested if the results are similar in an European or Norwegian context. 4) Multi-benefit assessment of NbS is difficult, however it is necessary to uncover the full potential of NbS interventions and make them comparable with traditional and engineered solutions.

The principles of multi-benefit assessment that has been developed in DeSCIPHER can be taken forward by other researchers that work in the field of nature-based solutions (NbS) and ecosystem service assessment. Research cooperations started in this project, will hopefully extend to new projects and funding. The successfully testing of the new payment vehicle “willingness to contribute space” in a choice-experiment survey in China offers a possibility for economists to use this payment vehicle in cases where space is a scarce and highly contested resource. NIVA aims to acquire new funds in order to refine this methodology and test it in an European and/or Norwegian context. DeSCIPHER results are also of importance for non-academics, especially for urban planners. The multi-assessment framework helps to enable them to optimise planning of future urban NbS. However, the results from the modelling exercises indicated once more that the performance of NbS is context and location dependent, thus NbS performance may vary from place to place, and careful consideration of local conditions is necessary. Especially for growing Norwegian municipalities with the need to densify (i.e. the Oslo metropolitan area) it is important to find enough space for NbS and greenspaces. Access to private space for this purpose is therefore very important and using the payment vehicle “willingness to contribute space” would therefore be very interesting. Even though the choice experiment was run in China, it has shown that there is a potential for saving money when rolling out more NbS through involvement of citizens – not only by using their willingness to pay, but also by engaging them in the maintenance of NbS or by accessing private space for NbS. If this finding can be confirmed for Norway/Europe, it opens up for new ways of public engagement.

Climate change will intensify current urban problems like flooding, water quality, high temperatures and air pollution. In China, where cities are expanding rapidly, and Europe, there are opportunities to better manage the greenspace (parks, trees, woodland) and bluespace (rivers, lakes) to provide multiple benefits to people. The project "Designing Sponge Cities for multiple benefits: integrating nature-based solutions to create sustainable places - through Innovation, Policy, Health and Environmental Research (DeSCIPHER)” project uses the idea of ‘Sponge Cities’ where nature-based solutions’ soak up high rainfall, reduce water and air pollution, high temperatures and noise, and improve recreation and health opportunities. We will work with businesses to design and finance innovative solutions in Chinese and European cities, which can be followed around the world. New and existing case studies will provide an evidence base for the design principles of long-term successful interventions; and the effective involvement of the public and business in sustainable urbanization. Development of successful solutions will be driven by joint initiatives with the business sector, planners and scientists, in turn sustaining further innovation.