With much of New Zealand’s water infrastructure particularly vulnerable to the growing dangers of climate change, Iain White and Alexandra Keeble argue that investing in new systems and flexible solutions are key to future-proofing for an uncertain future. 

It’s not something you expect to see on the streets of New Zealand: raw sewage bubbling up into floodwater and seeping into homes, schools, businesses, and public spaces.

We think of what happened in Edgecumbe as the worst-case scenario, the extreme event we can expect to occur every 50, 100, or 500 years.

But in 2017, this also happened in Auckland, Christchurch, Rotorua, and Dunedin to name five major cities alone. Intense rainfall is causing our storm and wastewater infrastructure to fail more often and in more places, and scientists are better understanding how climate change is influencing this change.

Climate change is expected to cause a rise in sea levels, an increase in extreme rainfall events, more severe and frequent coastal storms, and (a somewhat miserable irony) more droughts. Each of these will affect our stormwater and wastewater assets in the following ways.

• Sea levels increased by around 19 centimetres over the 20^th century and are predicted to rise another 30 centimetres in the next 50 years. We can expect coastal infrastructure to become more vulnerable, more often. Infrastructure will not just be vulnerable to flooding but also to saltwater corrosion. Our drains – which tend to rely on gravity – will perform less well.
• More severe storms are predicted, which means we should expect more flooding, physical damage to networks, and electrical failure at treatment plants.
• Away from the coast, the changes in extreme rainfall events mean that the design parameters of infrastructure will be exceeded more often. This will cause more frequent flash flooding and an increase in times when wastewater overflows and pollutes our water.
• Drought also affects our infrastructure, disrupting gravity systems by slowing flow and leading to blocked pipes. Severe droughts can also affect wastewater treatment processes which can create functional and safety concerns.
• We can also expect more cascading impacts, such as people and businesses being affected as the infrastructure they rely on fails. Although we still don’t know enough about where this will unfold and over what timescales.

These effects won’t be distributed equally. Some parts of New Zealand will be affected sooner and more severely than others due to their geography and the nature of their infrastructure. And flooding and infrastructure failure doesn’t just cause obvious and visible damage: it also affects our ecology, public health, private sector investments, and public purse.

Stormwater and wastewater assets in New Zealand are worth well over $20 billion, and largely, they have not been designed with climate change in mind as much of our infrastructure predates the science. Climate adaptation will likely require significant and expensive changes to our stormwater and wastewater networks and, under current arrangements, councils bear the responsibility. As they already struggle to pay for the new infrastructure required to release land for growth and face pressure to keep rates and development contributions low, this is not an easy task.

So, what can we do about it? How do we (or our elected representatives at local government) make good investment decisions with costs that are proportional to the risks? Perhaps most importantly, how can we design our infrastructure not for the one-in-a-100-year flood today, but for the incremental and uncertain changes that are part and parcel of climate change?

First of all, we actually need to talk about climate change so that we can better understand the risks to our stormwater and wastewater systems. Under the mantle of the Impacts and Implications Programme of the Deep South National Science Challenge, we recently brought together academics, scientists, industry groups, policymakers, water service providers, and consultants to identify the current the state of current knowledge. We also analysed how we expect climate to impact on our wastewater and stormwater infrastructure, and outlined what we need to know to make better decisions that make sure we can experience the same protection and performance in the future as we do now.

In short, if we want things to stay the same, things will have to change.

We need research into the direct and indirect impacts of climate change on our infrastructure. This will allow us to understand the scale of the problem and the ways that climate change will unfold, in what places and at what timescales. We can then use this evidence to decide how to act. Do we need to retrofit some settlements more urgently than others? How can we ensure that the current growth boom across New Zealand isn’t storing up problems for future generations? Perhaps it’s partly about being smarter about how we deal with water, detaining it before it enters the pipes, to help the infrastructure cope. Perhaps it’s about designing a network which has parts that are ‘safe to fail’, with places for water to go safely in times of need. Perhaps it’s about incorporating more green infrastructure into our towns and cities.

This is not unusual internationally. For example, over the next 25 years, Philadelphia is aiming to return one-third of its hard surfaces into porous vegetated gardens and parks to absorb, filter, and store stormwater. As part of its wastewater treatment, the city is also restoring wetland and waterway ecosystems to enhance the natural filtration of pollutants.

We also need urgent research into how we govern this problem. What role can central government play in coordinating across different scales and sectors? Do we need to move towards a catchment-based approach which links what’s happening upstream and downstream in an integrated manner, as Europe has had to consider recently when faced with similar problems of flooding? And who pays? Is this a local problem where ratepayers in certain cites will pay an unfair burden of costs? Or is it a national one? This is an example of an area where, perhaps, a new Climate Change Commission can help cut across what is currently a fragmented and siloed way of operating.

We need to make it easier for decision-makers (whether they’re in local or central government) to plan for an uncertain future and to invest in systems that are flexible so that we’re not stuck with unsuitable decisions for a generation or more.

Filling these research gaps will help Aotearoa New Zealand reduce future disruption and cost by adapting to our changing climate.

The Climate Change and Stormwater and Wastewater Systems report, commissioned by the Deep South National Science Challenge, highlights infrastructure issues Aotearoa New Zealand may face as it grapples with “increasingly severe risks” of extreme rainfall, storm surges, sea level rise and drought.

The Spinoff’s science content is made possible thanks to the support of The MacDiarmid Institute for Advanced Materials and Nanotechnology, a national institute devoted to scientific research.