Image caption and credit: Small-scale sponge city application, green roof. Chuttersnap/Unsplash
In recent years, residents of Atlantic Canada have faced recurrent flooding, triggered by subtropical storms, such as Lee, or by very intense rainfalls, such as the one that caused a Nova Scotia-wide state of emergency to be declared in July 2023. Increasingly frequent heavy rainfall events damage properties, infrastructure, people’s and ecosystems’ well-being. While these events pose challenges for emergency management due to their unpredictability and increased frequency, it is possible, with the collaborative efforts of residents, political leaders, and decision-makers, to limit storm impacts. One solution gaining traction globally is the ‘sponge city’ approach, already successfully applied in China, the United States and countries across Europe.
Understanding Sponge Cities
Sponge cities are urban areas that imitate natural ecosystems, particularly in their approach to rainwater management. They are nature-based approaches reliant on blue and green natural infrastructure for stormwater management. Sponge cities aim to handle rainfall at its source instead of directing runoff into engineered (gray) stormwater infrastructure systems. This technique manages on-site stormwater and reduces flooding. Since the water remains where it landed, it is also less likely to pick up pollutants harmful to the natural ecosystem. They also help reduce the need to upgrade and expand gray infrastructure over time. Sponge city approaches do help; Portland (OR, United States) found that after they implemented sponge city strategies on NE Siskiyou Street, peak flow runoff was reduced by 81%.
Explore examples of sponge city projects at different scales in the photo gallery below.
Image 1: Medium-scale sponge city application: Glencrest Park rain garden project (Markham, ON), before (left) and after (right), Toronto and Region Conservation Authority. Image 2: Medium-scale sponge city application: urban wetland in the Humber Arboretum (Toronto, ON), Humber Arboretum. Images 3 & 4: Large-scale sponge city application: a mangrove park in the place of an old landfill (Sanya, Hainan, China), Turenscape. Image 5: Medium-scale sponge city application: Lorne Street Stormwater retention pond (Sackville, NB), Town of Sackville. Image 6: Small-scale sponge city application: bioswale by a highway (United States), Caltrans, State of California.
The first country to utilize the sponge city approach was China, where urbanization and a climate with typhoon seasons near its coast has led to water management problems. After years of researching this approach, in 2014 the Chinese government called for the adoption of sponge cities in all new city developments nationwide. By 2022, there were more than 64 Chinese cities with legislation to implement sponge city guidelines for the local scale.
There are multiple factors that together make up for the success of any sponge city strategy — and they go beyond water management. Ecological, socio-cultural, policy and governance, and economic factors are just a few that influence the success of a project. Successful implementation of sponge cities require community and governmental support, enabling policies, and guidelines for local-scale implementation. In Atlantic Canada, similar considerations could enable the success of sponge city initiatives, where local policies, environmental factors, community support, and governance play key roles in shaping resilient solutions to flooding and climate change.
Sponge Cities in Atlantic Canada
Due to the region’s diverse geographic landscape, Atlantic Canada’s climate change challenges are multifaceted and include sea-level rise, coastal erosion, aging infrastructure, resident perceptions, and adaptation not always being decision-makers’ priority – among other challenges. Implementing sponge cities and their strategies could help to address these challenges.
While the term ‘sponge city’ may suggest a network of nature-based stormwater infrastructure systems, there is no clear guide on size and other design requirements for such strategies.This flexibility gives municipalities and developers the opportunity to adopt this concept on a wide range of site sizes. Some aspects of sponge cities applicable to Atlantic Canada include:
- Green infrastructure: Rain gardens, parks, bioswales, and permeable pavements can reduce the pressure on engineered (gray) stormwater management systems.
- Floodplain and salt marsh restoration: Restoring natural floodplains and salt marshes helps to absorb rainwater along the coasts and inland.
- Stormwater management: Techniques, such as low-impact development, are in line with sponge city approaches, and can capture and store rainwater.
- Municipal decision-making: Supporting and enabling policies and regulations encourage the integration of sponge city methods and design in public and private developments.
While sponge city applications are flexible in size and approach, scaling is crucial when it comes to utilizing it, along with zoning and land use policies. For example, changing one vehicle parking spot’s surface from concrete to permeable pavement will not solve an entire parking lot’s flooding problem. When sponge city strategies are applied on a large scale, urban areas become better equipped to handle heavy rain and flooding by acting ‘spongy’ and absorbing rainwater. On top of scale, more factors need to be considered to put sponge city strategies into action across Atlantic Canada:
- Policy frameworks: Governments of all levels, but especially the local level, need to develop policies to promote the sponge city concept.
- Funding and incentives: Financial support can motivate communities and developers to adopt sponge city strategies.
- Public awareness: Residents should understand the benefits of sponge cities and participate in decision making processes. Engaged and aware residents can be powerful advocates for sustainable development.
- Long-term vision: Political leaders should have a long-term vision for resilience that translates into policies and legislation.
The above is not to say Atlantic Canada has nothing in place that is already considered a sponge city approach. Many existing urban areas feature green infrastructure. The Climate Change Adaptation and Resilience Part 2: Lorne Street Naturalized Stormwater Retention Pond in Sackville, New Brunswick blog post explored one example of making a city more “spongy” to improve water management. However, isolated projects like this come with limitations. Scaling sponge city projects is crucial, otherwise they do not enable real change and only lead to reduced flooding on the block or subdivision level. Site-specific projects can reduce flooding at the block or subdivision level. Connecting multiple projects together over time can help match the increasing intensity of rainfall events and serve a larger geographic area.
Although there is no silver bullet solution that can completely eliminate flood risk, the sponge city approach offers numerous benefits. It augments gray stormwater management infrastructure in a scalable way; makes use of existing natural features such as marshes, green spaces, fertile valleys, and forests; enhances biodiversity; and reduces urban heating. Protecting, expanding, and connecting existing natural features and sponge city components can help bring this approach to new locations within a community to foster ecosystem, infrastructure, and social resilience.
Griffiths, J., Ka Shun Chan, F., Zhu, F., Higgitt, D. L., (2022). Interpretation and application of Sponge City guidelines in China. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.
Hawken, S., Sepasgozar, S.M.E., Prodanovic, V., Jing, J., Bakelmun, A., Avazpour, B., Che, S., Zhang, K. (2021). What makes a successful Sponge City project? Expert perceptions of critical factors in integrated urban water management in the Asia-Pacific. Sustainable Cities and Society.
Shephard, M. W., Mekis, E., Morris R. J., Feng, Y., Zhang, X., Kilcup, K., Fleetwood, R., (2014). Trends in Canadian Short‐Duration Extreme Rainfall: Including an Intensity–Duration–Frequency Perspective. Atmosphere-Ocean, 52:5, 398-417.