Frequent flooding in NZ – Expert Reaction

Last weekend’s wild weather provoked severe flooding in the Buller and Marlborough regions – the third major flood event in New Zealand this year.

Residents, farmers and authorities face much work ahead to repair and rebuild, and it’s estimated hundreds of people have been displaced.

The SMC asked experts to comment on the science behind this situation. 

Dr Judy Lawrence, Senior Research Fellow, Climate Change Research Institute, Victoria University of Wellington, comments:

“The total disruption we saw from the heavy rainfall over the weekend on the West Coast and Marlborough is consistent with a changing climate that is warming and able to hold more water before dumping it. We can expect more of this. It is a global phenomenon – but our exposure in New Zealand to such extreme pluvial events is a timely reminder that we not only have to prepare for them, but also plan our way out of the most severe impacts and shift from our reactive mode to anticipate where the worst effects will be felt.

“We have relied too long on stopbanks, which will never protect us from all eventualities as we saw in Marlborough. We have a legacy of development behind stopbanks, which creates a false sense of security to communities, and warning systems alone may save lives but not the disruption as we have seen on the West Coast and Marlborough this weekend.

“We have councils consenting more development in at-risk areas and even offering ‘protection’ and raising land and floor levels for further development to meet our housing shortage – and being funded to do so by Government (Covid infrastructure funding). Our housing stock typically lasts much longer than the 50 years in our Building Act and impacts of climate change are near-term issues that we are compounding for future generations to deal with.

“We seem deaf and blind to the science and the tools and methods for planning that we have available to address these risks. How much disruption can communities take before planning kicks in to reduce risks and plan for more of the extreme events and ongoing changes like sea level rise, which exacerbate hazards already being felt?

“In coastal communities, the coincidence of heavy rainfall and rising seas – especially on extreme high tides – will challenge us and these are certain climate change effects. Preparation includes a response to the Government’s National Adaptation Plan due for consultation later this year, and identification of particular hotspots that we know of already – and those that we know will emerge before mid-century. Asking what will trigger a response to preemptive planning – and thinking about when we need to start the planning based on the coping capacity of the current generation of those affected with a long view to the future – is a conversation that must get going without delay.

“However, while we have this conversation, the legacy consents continue to be granted. Something is urgently needed to address the hiatus until the new Resource Management laws are completed.”

Conflict of interest statement: Dr Judy Lawrence is a Climate Change Commissioner and the views above are based on her research and do not represent those of the Commission. Judy receives research funding from the Resilience Science Challenge, the Deep South Science Challenge, and the SeaRise Endeavour funded programme, as a Senior Research Fellow at the Climate Change Research Institute at Te Herenga Waka Victoria University of Wellington.

Professor Bruce C. Glavovic, School of People, Environment and Planning, Massey University, comments:

“For those who have lost cherished possessions, faced frightening conditions, and the prospect of a slow and costly recovery, our continued support is vital as the days and weeks go by.

“Many struggle to make sense of why it is that 1-in-100-year flood events seem to be occurring much more frequently than once every hundred years. This is because the phrase – ‘100-year flood’ – is a simplified description of a recurrence interval of a flood level with a one per cent chance of occurring in any given year. Such flood levels can be reached in two successive years based on statistical chance alone. However, the reality of climate change is that some parts of our country are experiencing more frequent extreme weather events; and so flooding may become even more intense and frequent in some parts of the country.

“There are three key considerations for addressing flood risk in a changing climate. First, flood risk is to a large extent a product of legacy or historical decisions about where to locate our towns and cities. Much historic development took place at important river crossings or along low-lying shorelines. Living on the water is wonderful when things are calm. But such locations put people, and the things they value, in harm’s way. The most effective way to reduce flood risk is to ensure that current and future decisions about so-called ‘greenfield’ development (opening up undeveloped land for residential, industrial and / or mixed use) does NOT take place in hazardous locations – such as in floodplains, along low-lying shorelines, on steep, unstable slopes, or on fault lines, etc. Tragically, some local communities and their governing authorities ignore this long-standing guidance, and continue to put current and future generations at risk by approving new development in such locations – against the spirit and intent of long-standing laws, policies and guidance.

“Second, exposure to flood risk is only one side of the coin. The other consideration is how susceptible to harm are the people in these locations. The prospect of disaster looms large when people in harm’s way are poor, with limited political and economic influence, and are vulnerable to adverse impacts. Reducing flood risk depends on how effective we become in reducing social vulnerability. Compared to our understanding of the flood peril (based on natural sciences), our understanding about social vulnerability to flood risk in a changing climate (based on social sciences and the humanities) is woeful.

“Third, tackling flood risk is a long-game. In other words, it is not a problem that we can solve overnight. We need to take step-wise actions, starting with a focus on those most exposed and vulnerable to harm. And then work progressively towards future proofing our towns and cities, many of which are along rivers and shorelines that will experience escalating climate change-compounded impacts in the coming years and decades. Adopting more proactive and anticipatory adaptation pathways planning approaches will help to make necessary short-term decisions without foreclosing future options. In some localities, managed retreat will become an absolute necessity, especially along the shoreline as sea level continues to rise – despite the traumatic cultural, psycho-social and economic consequences.

“The time has come to face up to this reality. We need to ensure that there is an effective and equitable funding mechanism in place to support managed retreat of the most exposed and vulnerable communities. We need to improve public awareness and understanding about this imperative, and develop the institutional capability to facilitate this process. This requires institutional support from central to local government and iwi authorities. We face turbulent times in coming years. We have much to learn from tangata whenua about how to make such decisions in the best interests of both current and future generations.”

No conflict of interest.

Dr Luke Harrington, Senior Research Fellow in Climate Science, NZ Climate Change Research Institute, Victoria University of Wellington, comments:

“If you were to pick any time of year and location in Aotearoa where extreme rainfall lasting several days shows a robust signal of becoming more intense and more likely because of climate change, I would pick the West Coast of the South Island in the wintertime.

“This event looks to be another filament of intense moisture coming from the tropics (in this case, possibly originating in the Indian Ocean) – this is called an atmospheric river. The rain was likely made worse due to sea surface temperatures also being warmer than average over the past few months – which itself is made more likely with climate change.

“Three papers were published earlier this year – titled Extreme rainfall in New Zealand, A Climatology of Atmospheric Rivers in New Zealand, and The impact of atmospheric rivers in New Zealand – all confirming a long-suspected fact that New Zealand is one of the most susceptible countries in the world, when it comes to extreme atmospheric river impacts. The first paper in that list shows that nearly all of New Zealand’s most costly rainfall events in recent history were directly linked to atmospheric rivers.

“An atmospheric river is identified largely based on how much moisture is being transported through the atmosphere – so how much water vapour is in the air and how fast that air is moving. In most parts of the world, atmospheric rivers are expected to become more intense and frequent with climate change, but this is only due to an increase in the moisture-carrying capacity of the atmosphere as temperatures rise.

“Around New Zealand, however, we know that the westerly winds are strengthening in the wintertime with climate change. So in a warmer world, both the amount of moisture being carried will increase, and the speed with which that moisture is moving towards population centres on the West Coast of the South Island is also speeding up. Combined, this means that we expect the same bad weather system to lead to more rainfall than it otherwise would – without climate change – and this is particularly true for the Buller and Marlborough regions, since they are stuck between these incoming moisture-laden systems, and the Southern Alps forcing the air to compress and the rain to fall.

“So that’s why we are confident that wintertime extreme rainfall over the West Coast of the South Island will be more intense and frequent because of human influences on the climate.

“In terms of quantifying real numbers, we would have to perform a specific attribution analysis with high-resolution climate models to get a robust answer. But based on similar previous analyses, I would anticipate this event being no more than 10 per cent more intense when compared to a world without climate change. This might translate to an approximate doubling in the likelihood of seeing a similar event striking a similar region (again, when comparing the present day to a hypothetical world without climate change). But further research is needed to fully quantify the exacerbating impact of climate change on this weekend’s severe rainfall.”

No conflict of interest.

Professor Ilan Noy, Chair in the Economics of Disasters and Climate Change, Victoria University of Wellington, comments:

“If we want to know how to adapt and respond to future disasters, we need to know two crucial pieces of information: how much these disasters cost us, and how the probability and intensity of these events has already changed – and how it will continue to change – because of climate change.

“There is a lot of ongoing research that can inform us on the second point, but surprisingly we don’t really know how much these disasters (including the one last weekend in West Coast, Marlborough, and Wellington) cost us right now. We need to start counting these costs, if we want our future policy to be based on evidence rather than on guesswork and intuitions.”

No conflict of interest.

Associate Professor Asaad Shamseldin, Faculty of Engineering, University of Auckland, comments:

“In more recent years, extreme flood events have become more frequent in New Zealand. This has been illustrated by the recent floods in the West Coast of the
South Island.

“These events can be the result of climate change and can be the norm under a changing climate. These events have caused significant disruptions and
damages to our communities. It also caused damages to some essential infrastructure, as well as putting some infrastructure under considerable risks. The
impacts of these events can also be exacerbated by land-use changes.

“In New Zealand, there is an urgent need to reevaluate the risks associated with extreme floods under a changing climate. There is also a need to develop and implement effective adaptation plans to protect our communities from the adverse flood impacts. We also need to evaluate what is the acceptable risk for our communities which is essential for developing a road map to deal with adverse flood impacts.”

No conflict of interest.