Sponge Cities: Can they help us survive more intense rainfall?
This report was authored by Kali Mercier, Deputy Director at Mahi a Rongo Helen Clark Foundation, in partnership with WSP New Zealand and was awarded the Category winner, Research and Communications, at the recent Resene NZILA Awards 2024.
We can make our cities more resilient to climate change by making them more absorbent. The report recommends a series of actions to respond to the escalating impacts of climate change-induced extreme rainfall events. These include excluding vulnerable flood-prone areas from development and incorporating mātauraunga Māori knowledge to minimise urban flood risk. You can read the Sponge Cities report here.
Report author Kali Mercier says sponge city approaches to stormwater management must be urgently explored to help fortify the country against climate impacts and reduce urban flood risk. While creating spongier places and spaces on a large scale across Aotearoa New Zealand’s many towns and cities will cost, not doing it will ultimately be much more expensive.
“We really do not have any other alternative if we want to avoid loss of life and property in the long term.”
Kali says in many places our current approach is falling short. “With climate change predictions showing increased extreme rainfall, we must act urgently, decisively and strategically to address urban flooding. Our aging stormwater infrastructure is increasingly unable to cope, now, with deluges that are all-too-frequently causing catastrophic damage – let alone five, ten, or twenty years into our shared climate future.
“Catastrophic flooding events in Nelson / Marlborough in August 2022, and in Auckland in January, highlight the urgent need to better adapt our urban areas to these inevitable changes. The development status quo of covering every available inch of surface with concrete isn’t helping. Building across the natural flow path of water creates larger issues.
“We’re losing valuable green spaces which make our cities more absorbent. When the heavens open, the water has to go somewhere. We’ve created the problem by building in the wrong places, such as the bottom of floodplains or over existing water flow paths.”
The report finds that when sponge city or ‘nature based’ approaches are deployed alongside conventional engineering solutions and stormwater infrastructure upgrades, they’re effective at supporting and enhancing community resilience.
Inspired by ancient Chinese farming techniques, the concept of sponge cities promotes working with water rather than against it, by ‘daylighting’ streams, reducing impervious surfaces, enhancing green spaces, and implementing green infrastructure.
With plenty of blue-green natural features, sponge cities allow water to flux and be absorbed, stored, and slowly released into the environment – mimicking natural hydrological processes. They’ve also been shown to benefit biodiversity and human wellbeing by creating new habitats and amenities in urban areas.
International evidence shows that sponge city approaches can be one of the best proactive measures towns and cities can take to minimise future flood risk.
WSP Technical Principal for Water Liam Foster says using nature-based and sponge city solutions to create space for the waterways to slow down, detain and retain water is a clear and immediate action we can, and should, take.
“With a strong focus on the natural flow of water and ecosystems’ ability to absorb water, mātauranga Māori knowledge will play a vital role in Aotearoa’s path to a spongier future.
“For this to work as part of a truly national stormwater solution for our urban areas, everybody from local and central government agencies, private industry and even individual homeowners need to be engaged.
“The report emphasises several crucial actions, such as coordinated planning at national and local levels to maintain space around flow paths and waterways, as well as initiating retrofitting of green infrastructure as a pragmatic starting point for all towns. Vulnerable flood-prone areas should also be excluded from new development.
“Let’s get behind this report and work together to kickstart a future ready conversation around making space for water – one that underpins why a sponge cities approach is desperately needed to help build Aotearoa’s climate-resilient urban future.”
Report recommendations include:
Retrofit our cities and towns to become sponge cities to help us survive and thrive despite increasing rainfall associated with climate change. Take a holistic, nature-based approach to ensure we also capture benefits for biodiversity and human health and wellbeing.
Act urgently and decisively, and plan strategically for the long-term at the national, regional, and local levels. Name and prioritise nature-based sponge city approaches as a key climate adaptation approach for Aotearoa New Zealand.
Develop a clear vision for a sponge cities model for Aotearoa New Zealand that draws on our strengths and unique context, such as mātauranga Māori, and community-led nature-based initiatives.
Develop and agree a national funding approach that is coordinated and comprehensive.
Incentivise and/or regulate for a range of ‘spongy’ solutions on public and private land, and in new developments.
Heather Wilkins, Kali Mercier and Alan Whiteley
This news release was originally shared by the Helen Clark Foundation and can be read in full on their website.