PHOTO: Vidar Nordli-Mathisen/Unsplash

The impact of back-to-back storms – Expert Reaction

Cyclone Gabrielle is looking “more and more likely” to hit our northern shores as early as Sunday. This comes roughly a week after Auckland began its clean up efforts from a record-smashing deluge across the North Island in January.

So how do the cumulative impacts of such storms affect community resilience, water infrastructure, and our wider environment?

The SMC asked experts to comment on the following:

1. Post-disaster recovery
2. Nature-based solutions for stormwater management
3. The impacts of floods on our coasts and estuaries

Associate Professor Siautu Alefaio, School of Psychology, Massey University, comments:

“In this new era of compounding disasters, we are in the midst of one disaster (pandemic) when pummelled with the next (flooding), and then another (Cyclone Gabrielle). Resilience is most definitely put to the test. Bouncing back continuously from one disaster to another is exhausting and does take its toll. Communities are not immune. The new realities of displacement, uncertainty and vulnerability are now common-place.

“So how do communities stay resilient in the face of compounding disasters? It depends entirely on how we are as a nation, community, village, family. I’ve said continuously in previous disasters, the state of a nation prior to a disaster will determine how they recover. If as a community or nation we work together, are helpful and responsive to those displaced, poor and vulnerable. Have emergency management systems that align and work in unity with local community services. Courageous leadership that is not influenced by racism, elitist arrogance or fear of other races/ cultures and how they do life. Basically, we are an equitable society. Then, our resilience to the severity of climates of change can withstand this new tide of compounding disasters, whether it’s you today or me tomorrow.

“The reality is communities are resilient, in vulnerability there is also strength. We have seen this in the most impoverished communities, where the poorest of Aotearoa give to the poor, and generosity of spirit kicks in. This is community resilience at its best. But, as the number of disasters increase the resilience of this community spirit will wane. It is a long game, so the team of five million will need to empathise and mobilise in order to support each other.

“Yesterday it was Christchurch, today it is Clover Drive – Henderson Auckland, tomorrow we wait with bated breath, hopefully better prepared than we were last week.”

No conflicts of interest.

Professor Christine Kenney, Professor of Disaster Risk Reduction, Massey University, comments:

“Cascading natural hazard events fuelled by climate change are the new norm for Auckland. Families and communities should be anticipating that cyclones, floods and other catastrophes will be occurring more frequently and planning ways to stay safe. Equally, local authorities should be stepping up to ensure that residents have access to essential resources and services. Timely accurate and regular communication with all sectors of the community regarding what and where emergency support is available and how to access it will be key.

“Outreach by local community agencies and NGOs has been very evident in response to the recent floods, yet there has been a relative silence in the media and elsewhere regarding the community assistance offered by various groups. As exemplars, Te Whānau o Waipareira Trust continues to provide effective outreach in West Auckland, Māori wardens have mobilised to assess needs, Te Puia Marae is still housing evacuees, and Pacifica initiatives in South Auckland have provided wide spread support in the form of meals and accommodation. Ensuring effective recovery from future disasters will require genuine collaboration and regular communication with these diverse sectors of wider Auckland to ensure disaster responses are well-coordinated, resources are allocated appropriately, and all parts of the Auckland community receive essential support.”

Conflict of interest statement: “N/A but I am a member of the Ministerial Advisory Committee on Emergency Management.”

Dr Annette Semadeni-Davies, Urban Aquatic Scientist, NIWA Auckland, comments:

“The Auckland floods have shone a light on nature-based alternatives to traditional pipe-based drainage networks. In the central city, land use intensification has increased surface runoff. In addition, the Auckland stormwater system is aging in places and was not designed for climate change-driven extremely high intensity rainfalls. The combination of extreme rainfall and limited capacity to cope with high runoff volumes in the system led to widespread flooding.

“After the storm, there have been several recommendations for improving flood management in Auckland, including nature-based solutions. Those suggested include rain gardens, vegetated swales, living roofs and walls, infiltration strips, tree-pits, constructed ponds and wetlands. Such solutions are cost-effective for day-to-day stormwater management; their main functions are to remove contaminants from stormwater and to reduce peak flows from non-extreme high intensity rainfalls.They can also provide a range of social, cultural and ecological co-benefits to urban areas, including habitat creation, passive cooling of the urban heat island, provision of walking and cycle ways, and landscaping. While important for protecting our urban water environments, they will not be adequate for the level of flooding we have recently seen on their own.

“It is vital to distinguish the nature-based solutions used for stormwater management from those used for flood protection, lest the public lose faith in these valuable assets if they fail to hold back flood waters. Nature-based solutions for flood protection, such as flood-basins, are larger than those for stormwater management. They are designed for rainfalls with a return period of decades compared to return periods of two to five years for stormwater management. The distinction between nature-based solutions for flood protection and stormwater management is important as the design for an effective ‘sponge’ to soak up flood waters may not be cost-effective for stormwater management and those intended for stormwater management may not have sufficient water storage for flood protection.

“Moreover, to maximize ‘sponginess’, solutions for flood management need to be ‘squeezed’ before the next rainfall, just like squeezing out water from a dish cloth before it can be used again. The short time between ex-tropical storm Hale and the deluge on January 27 meant that nature-based solutions based on infiltration would likely already wet because they take time to empty. In contrast, nature- based solutions for stormwater management need extended storage of a day or more for water treatment, and even longer for rainwater harvesting. This means that a balance is required between operating nature-based solutions for water quantity control (keeping them empty between storms), water quality control (maximizing detention times for water treatment by slowly releasing water) and water reuse (retaining water for use in dry weather).

“There is also the issue of where nature-based solutions should be located. Those currently used for stormwater management in Auckland are mostly in new developments where they were part of the urban design. Larger nature-based solutions for flood protection, such as flood basins, will require land that may not be available and will be difficult to retrofit in the highly developed isthmus area.

“There are several options that could be explored for flood management in Auckland. One option is real time control of flow through pipes during high flow events (for example, by draining stormwater storage infrastructure before the onset of forecasted heavy rainfall, avoiding bottlenecks and surges, and diverting water away from critical infrastructure or densely populated areas). Other options include construction of underground cisterns, using existing low-risk amenities such as playing fields, parks and carparks as flood basins (there are already several examples of this in Auckland), managed retreat from vulnerable areas and continued maintenance of and upgrades to existing drainage infrastructure.”

No conflicts of interest

Conrad Pilditch, Programme Leader for Degradation and Recovery, Sustainable Seas National Science Challenge; and Professor of Marine Science, University of Waikato, comments:

“In January and February, there has been massive amounts of climate-related flooding across Aotearoa. While there’s undoubtedly a cost to the onshore clean up, what Sustainable Seas research reveals is an unseen cost — to our estuarine and coastal ecosystems.

“With much more flooding set to come in the future, these climate-related events will push estuary ecosystems to the brink of collapse and some may never recover.

“Flooding increases the amount of sediment and nutrients flowing into our estuaries affecting the primary producers, which are the base of the coastal food web. It can also modify species behaviour and what species we find. These stressors interact with others (e.g., over harvesting, heavy metal contamination, macro-algae blooms, habitat loss) and build up over time generating cumulative effects.

“Our research reveals that an increase in turbidity reduces the amount of sunlight able to filter through the water and onto the seafloor. This impacts the small microscopic plants on the seafloor (microphytobenthos or MPB) reducing production with implications for the entire food web. Turbidity is considered a good measure, or indicator, of water quality.

“The more an estuary is flooded, the more turbid it becomes, eroding ecosystem health and increasing its vulnerability to a tipping point. A tipping point is a rapid transformation that happens when an ecosystem has lost its capacity to cope with change and restore itself to balance. Tipping points often involve the loss of valuable marine resources and ecosystem services. For example, death/removal of filter feeding by shellfish may result in a rapid decline in water quality especially if combined with even a small increase in plant nutrients.

“Even in healthy estuaries, a sudden shift to poor water clarity caused by widespread flooding can decrease the growth of photosynthesizing organisms, such as seagrass and microphytobenthos (MPB).

“MPB are tiny (microscopic) photosynthetic organisms living on, or in, sediment on the seafloor. Just like seagrass, they are the foundation of coastal food webs.

“The more estuaries are altered by flooding, the less ability they have to filter and trap sediment. Studies all over the world have shown how healthy seagrass meadows & shellfish beds, for example, are able to reduce the concentration of suspended sediments in estuaries lowering the turbidity.

“These changes to species who are the foundation of estuarine ecosystems may also impact the behaviour of other marine life higher up the food chain.

“For example, international research shows kuaka (bar-tailed godwits) need the essential fatty acids produced by MPB to support their long migration from Aotearoa to western Alaska each year.

“With the degradation of the inter-tidal zone from flooding, MPB are compromised because they can’t photosynthesise effectively and have less sandy habitat to live in.

“Of course, kuaka may adapt to this change and seek a different food source, because seabirds are very good at adaptation. But MPB will continue to be negatively impacted by loss of water clarity.

“Earlier Sustainable Seas research proves what happens in estuaries also affects our ocean ecosystems, because sediment and nutrients are carried by river eddies over 100 km out in the sea’s surface; while submarine canyons connect coastal and deep-sea ecosystems, transporting materials from the land into the deep. This means that our environmental footprint goes much further into our marine Exclusive Economic Zone (EEZ) than previously thought.

“That’s why it’s vital we enact placed-based strategies and ecosystem-based management (EBM) to limit the amount of sediment and nutrients in Aotearoa’s estuaries and give them the best chance of surviving the impacts of climate-related events.

“Otherwise, we may stand to lose these precious resources and species forever.”

No conflicts of interest declared.