Climate change

Climate change: what ancient caves reveal about future New Zealand floods


Prehistoric deposits left in ancient New Zealand caves – like the Waipuna Cave in Waitomo – could help scientists better understand how precipitation changes as our climate warms. Photo / Supplied

Scientists are looking to prehistoric clues left in New Zealand caves to predict how climate change will cause deluge in our warmer, wilder future.

Researchers have long used records of prehistoric warm climates, trapped in sediment in ice cores, to better understand the potential rise in temperature as carbon dioxide concentrations warm our atmosphere.

Replenishing precipitation from those mild periods long ago in our planet’s past, however, is much trickier.

In New Zealand, precipitation records go back only to post-colonial development, when instrumental recordings first began.

Beyond this period, New Zealand’s past climate and rainfall patterns remain unknown, except for broad trends in relative humidity or drought over the past few thousand years.

“Because people have been recording precipitation for less than 200 years, we have a very limited picture of how precipitation regimes change when global climate transitions occur,” explained Dr Adam Hartland, a geochemist at the University. from Waikato.

“We know from paleoclimatic records that earlier in the current interglacial period we live in, about 9,000 years ago, it was wetter and the temperature of the atmosphere was slightly warmer than it is today. hui.

“Yet we cannot say that the precipitation in Hawke’s Bay, for example, was 50% higher than today.”

This was a critical knowledge gap for this country, which depended on rainfall but also remained vulnerable to too much or little of it.

In 2019, for example, a lack of rainfall on the North Island left hydroelectric lake levels low and forced the energy sector to resort to coal, increasing greenhouse gas emissions.

This year, a succession of storms driven by tropically laden “atmospheric rivers” caused catastrophic flooding that cost tens of millions of dollars in insured damage.

As our climate warms, scientists have predicted that New Zealand’s annual average precipitation will decrease in the northeast of the South Island and in the north and east of the North Island, but would increase in other regions.

University of Waikato geochemist Dr Adam Hartland pictured in Nurau Cave in the Cook Islands.  Photo / Garry K Smith
University of Waikato geochemist Dr Adam Hartland pictured in Nurau Cave in the Cook Islands. Photo / Garry K Smith

Droughts could also become two or three times more frequent in the eastern and northern regions by 2040.

Despite the variability from year to year, we have seen the southwest of the South Island become progressively wetter and the north of the North Island become drier, as well as more extreme events that carry the footprint of global warming.

With more humidity in the atmosphere, for example, the frequency and magnitude of arrivals from atmospheric rivers – which already account for half of New Zealand’s total precipitation – are expected to increase, and some research suggests their areas of strike are moving south.

Still, Hartland said building a detailed picture of the interplay between climate and rain in a maritime country like New Zealand remains notoriously complex even today.

“Right now, we are witnessing a major climate reorganization as the entire Earth system catches up with all the greenhouse gases we put out into the atmosphere,” he said.

Scientists venture into Wairoa's Cave of Disbelief.  Photo / Kate Clark
Scientists venture into Wairoa’s Cave of Disbelief. Photo / Kate Clark

“This inevitably leads to changes in the way the atmosphere and the ocean circulate, which in turn affects precipitation – but the question is how much and where?

“Because the way air masses interact with New Zealand’s oceans and land mass is so complex, even the most advanced models of climate physics and meteorology cannot make accurate predictions. and distant. “

This was where looking for clues into the planet’s past could help – and it turns out there was plenty to be found deep in the ground.

As water flowed through the earth over millennia, it dripped into caves depositing minerals and creating what are known as speleothems, including the well-known stalactites and stalagmites.

These deposits are unique because they are formed by the flow of water – a property Hartland and his colleagues will mine in a new million-dollar study.

Using a combination of state-of-the-art geochemical and magnetic methods, the team will study speleothems in the Waitomo and Wairoa regions to reconstruct precipitation from decades to millennia, dramatically increasing our understanding of gravity and gravity. frequency of droughts and floods.

“Using caves as archives isn’t really new to science, but when it comes to how we use these deposits and generate information from them, and help better quantify climate change, we are. at the dawn of a revolution. “

They also plan to study periods when the climate has changed rapidly, providing analogues of short-term climate states.

Scientists observe deposits in Waipuna Cave in Waitomo.  Photo / Sebastian Breitenbach
Scientists observe deposits in Waipuna Cave in Waitomo. Photo / Sebastian Breitenbach

“We can even go back 120,000 or 130,000 years in the past and compare samples from that time with others that are forming today, which is not possible with other types of paleoclimatic records,” did he declare.

“Because global climate models are tested against paleoclimatic data, our results will be critical in validating climate projections used by government for planning and adaptation at all levels of society. “

Importantly, the study, supported by the Endeavor Fund, sought to bring together past rainfall from different parts of the country – giving us a potential glimpse into how each region might fare.

“If we can find out that it was much drier on the east coast of the North Island 9,000 years ago, it may give us additional confidence to move forward and start planning for the challenges we are facing. are going to have for water and resources, “he said.

“If several dry years can really change the characteristics of a region, it behooves us to find out what that looks like – otherwise we might find that we are investing in infrastructure in places where we perhaps shouldn’t be.”

Create an “extreme fire”

Extreme fires - like that seen in major bushfires in Australia - are becoming a growing threat to firefighters and Kiwi communities.  Photo / Nathan Edwards
Extreme fires – like that seen in major bushfires in Australia – are becoming a growing threat to firefighters and Kiwi communities. Photo / Nathan Edwards

Meanwhile, another team of scientists will design some of the most formidable features of huge fires in controlled experiments never before seen in the world to better understand “extreme fires.”

Our changing climate is also increasing the frequency and severity of forest fires, and native forests once considered safe are now under threat.

It also increases the risk for Kiwi communities at the rural-urban interface – as shown by one of the largest forest fires ever seen in New Zealand, which ravaged 5,000 ha and destroyed nearly 50 homes. in Ohau, a year ago this week.

Today, the average annual direct impact of rural fires on our economy is estimated at around $ 140 million – but with a fire season that may have lengthened by 70% by mid-century, these total costs could reach around $ 550 million.

In the worsening picture, authorities worry about what is called an “extreme fire” – behavior that, until recently, had rarely been observed in New Zealand.

It is characterized by dangerous characteristics such as spots, where embers and other particles are thrown in front of the fire front; conditions of “explosion”, where hell suddenly escalates in size and intensity; and whirlwinds of fire and tornadoes.

All of these elements, but especially the vortices of fire, will now be closely observed and analyzed in an $ 11 million study led by Scion to better prepare the country and our firefighters for this new normal.

Scion fire specialist Grant Pearce said the experimental “burns” part of the program will mark the first known attempt to create and measure large-scale fire vortices – reaching tens of meters high – in field conditions.

“These will be carried out using residual forest fuels left over from the clearing of wild pines and will require very careful consideration and preparation to mitigate the dangers involved and the risk of escape.” “

A major fire, which occurred a year ago this week, destroyed nearly 50 houses in Ohau and damaged some 5,000 ha of land.  Photo / Otago Daily Times
A major fire, which occurred a year ago this week, destroyed nearly 50 houses in Ohau and damaged some 5,000 ha of land. Photo / Otago Daily Times

These types of experiments would help expand new theories predicting how and when fires got extreme.

“We no longer believe that fuels are the dominant factor causing these transitions, but assume that the coupling of fire front convection with atmospheric turbulence is the primary driver.”

And without having a clear understanding of this point of change, it has not been possible to develop effective tools and strategies to keep fire crews safe.

Still, Pearce said the program would explore and help develop potential new ‘smart firefighting’ technologies, such as drones, data systems and wearable sensors to give firefighters information about fires in time. real.

Elsewhere, the study would use models to simulate the spread of forest fires – drawing on work on the factors behind the Ohau fire – and also study the flammability of native forests, to through a mixture of tests and experiments.

Finally, the Kiwi and US research team planned to survey a range of people, from fire managers, boards and insurers to homeowners and developers, to identify barriers to planning and preparedness. fire hazards.

Pearce ultimately hoped the work, which is also supported by the Endeavor Fund, would help save lives, livelihoods, homes and ecosystems.


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