Speaker 1: Kielder. I'm Chelsea Daniels and this is a bonus episode
Speaker 1: of The Front Page, a daily podcast presented by the
Speaker 1: New Zealand Herald. Over the last year, the term atmospheric
Speaker 1: river has entered our daily vocabulary as New Zealand sees
Speaker 1: more intense rainfall hit our shores. From the Auckland Anniversary
Speaker 1: floods to two months worth of rain heading the East
Speaker 1: coast in just one day. The whole country seems to
Speaker 1: be susceptible to increase rainfall. But is this really the
Speaker 1: case and if so, what's the cause. Today on the
Speaker 1: Front Page, doctor Daniel Kingston from Otago University joins us
Speaker 1: to discuss their latest research into the cause and effect
Speaker 1: of rainfall in this country. Daniel, we've heard this word
Speaker 1: a lot in recent years, or this phrase rather, but
Speaker 1: can you explain what our atmospheric rivers?
Speaker 2: Well, the areas in the atmosphere where we see really strong,
Speaker 2: really intense transport of moisture vapor through the atmosphere in
Speaker 2: a long, thin section. So it looks a bit like
Speaker 2: a river when you look at a weather map of this,
Speaker 2: although it's not actually a river like we think of
Speaker 2: on the land surface.
Speaker 1: Right so literally, if we were looking at it from above,
Speaker 1: it would be kind of like a river above us.
Speaker 2: Yeah, it would certainly look like that in the sense
Speaker 2: that it's long and it's thin, and it's carrying an
Speaker 2: awful lot of water, but it's water vapor rather than
Speaker 2: liquid water itself.
Speaker 1: They seem to bring a lot of rain to New Zealand.
Speaker 1: But how much do these rivers of the sky contribute
Speaker 1: to our rainfall?
Speaker 2: It varies a little bit around the country. So in
Speaker 2: places like the west coast of the South Island, then
Speaker 2: we might be looking up up to eighty percent of
Speaker 2: our annual rainfall comes through these atmospheric river events. Places
Speaker 2: on the eastern side of the country maybe like Dunidan
Speaker 2: or christ Church a bit less, so maybe you know,
Speaker 2: we're talking less than fifty percent here. So it varies
Speaker 2: a bit around the country, but they're really important in
Speaker 2: some parts. And then particularly when we start to look
Speaker 2: at our heaviest rainfall events, then these do generally come
Speaker 2: from atmospheric river events.
Speaker 3: Meanwhile, heavy rain and strong winds have seen a state
Speaker 3: of emergency declared for part of Hastings after three breaches
Speaker 3: of the Home wan Sea Wall. Police are knocking on
Speaker 3: doors of affected residences to evacuate. The town of de Kataka,
Speaker 3: thirty kilometers from Gisbon, is cut off in both directions
Speaker 3: in State Highway thirty five between Gisbon and Tolika Bay
Speaker 3: is closed due to surface flooding.
Speaker 1: So this one's a new one for me. IVT or
Speaker 1: vertically integrated water vapor transport. Not quite as catchy as
Speaker 1: atmospheric river, is it? What does that mean?
Speaker 2: No? Not quite. Well, that's basically described how we measure
Speaker 2: how much water is being transported through the atmosphere. So
Speaker 2: when we're looking to say whether an atmospheric river is
Speaker 2: occurring or not, we look at this IVT variable vertically
Speaker 2: integrated water vapor transport. And so if that IVT is
Speaker 2: above a certain threshold and the kind the spatial pattern
Speaker 2: of IVT kind of matches what we expect of an
Speaker 2: atmospheric river, then we can say, well, this is an
Speaker 2: atmospheric river. And so if it's too low or if
Speaker 2: the shape isn't quite right, then it's not.
Speaker 1: Now I'm assuming that atmospheric rivers aren't anything new. Why
Speaker 1: do you reckon it's come into the public's consciousness.
Speaker 2: Now, Yeah, people first started researching them in the nineteen
Speaker 2: nineties and it didn't get picked up a huge amount initially,
Speaker 2: but kind of from the two thousands onwards, people started
Speaker 2: paying increased attention to it. Partly, it's just a catchy name,
Speaker 2: like you said, so it's something that people latch onto
Speaker 2: and gets a bit more recognition.
Speaker 1: It's visceral, isn't it.
Speaker 2: Yes, it is that everyone knows what a river's like.
Speaker 2: So yeah, it kind of really gives you a clear
Speaker 2: idea of what's going on. And then I think probably
Speaker 2: as people have become more and more aware of climate
Speaker 2: change and we've seen the effects that climate change has
Speaker 2: on some of our more extreme weather events, then you know,
Speaker 2: as we start getting more and more floods and damages
Speaker 2: from floods, then people naturally want to know what's causing it.
Speaker 2: And so there's kind of two things allided to give
Speaker 2: us this increased attention on atmospheric rivers.
Speaker 1: Well, you've absolutely segued perfectly into my next question. So
Speaker 1: you've recently worked on a study, hey, looking into the
Speaker 1: relationship between rainfall and climate change in New Zealand. What
Speaker 1: did your team investigate there?
Speaker 2: Ah? Yeah, So this is work done by a PhD
Speaker 2: student here at a tigo niftin Krishna and he's well,
Speaker 2: what we've been doing to together is looking for the
Speaker 2: trends in IVT over New Zealand and then trying to
Speaker 2: unpick what's caused those trends. So is it just that
Speaker 2: there's more water in the atmosphere and that's leading to
Speaker 2: a higher IVT or is it changes in the wind
Speaker 2: so it's wind speed getting stronger or weaker. You know,
Speaker 2: where's it coming from. So that's kind of been the
Speaker 2: key things that we've been asking and what we seem
Speaker 2: to have found is that certainly over the southern part
Speaker 2: of the country we are seeing higher IVT, so more
Speaker 2: moisture being transported over the country.
Speaker 1: If I whip out my year seven science knowledge, if
Speaker 1: the world is getting warmer, wouldn't that then mean that
Speaker 1: there is more water in the atmosphere because it gets evaporated.
Speaker 2: Yeah, that's right, No, you're exactly right. You know, we've
Speaker 2: got a warming planet, so that means that there's more
Speaker 2: energy at the surface that could be used to evaporate water.
Speaker 2: So as it gets hotter, we have more evaporation. But
Speaker 2: also as the air gets hotter, it can hold more moisture.
Speaker 2: So you know, if you keep evaporating, eventually the atmosphere
Speaker 2: will saturate and the water will have to fall out.
Speaker 2: But what we're doing to the atmosphere is increasing its
Speaker 2: capacity to hold that moisture, so the air can hold
Speaker 2: more moisture, so when a rain event does happen, there's
Speaker 2: more moisture in there that can be rained out. And
Speaker 2: that's why we expect to see and why we are
Speaker 2: seeing heavier rain events as climate change progresses.
Speaker 1: From your research, which areas of the country are most
Speaker 1: at risk from bearing the brunt of increased rainfall, it
Speaker 1: would be.
Speaker 2: The southern half of the country, particularly the western side
Speaker 2: of it. So in a general sense, our weather comes
Speaker 2: from the west. You know, it might be a bit
Speaker 2: more southwesterly or northwesterly, but generally it's from the west.
Speaker 2: So that means that the west coast of the South
Speaker 2: Island and the North Island experience those weather systems first,
Speaker 2: and so that's where the rain falls initially. That's why
Speaker 2: we know that the West Coast, as you know, wetter locations.
Speaker 3: Remaining Westport residents may be forced to evacuate this evening
Speaker 3: with serious flooding expectant to peak overnight. The rain delivered
Speaker 3: is predicted two months worth falling in just the last
Speaker 3: three days, with more on the way.
Speaker 1: So I'm here to say that global heating and climate
Speaker 1: change is really having an impact on rainfall.
Speaker 2: Yes, would be a simple answer. It gets a bit
Speaker 2: more complicated rainfall because it's so episodic in nature, it
Speaker 2: varies a lot from place to place. It makes it
Speaker 2: a lot harder to pick out a signal compared to temperature.
Speaker 2: Let's say there's always a temperature, we can always measure it,
Speaker 2: and it doesn't vary quite so much from place to place.
Speaker 2: It's much easier to pick out trends in temperature than
Speaker 2: it is in rainfall. But still we expect to see
Speaker 2: those extremes increase with climate change. But at the same time,
Speaker 2: we might expect our dry periods to increase as well,
Speaker 2: because if we've got higher temperatures, then that water will
Speaker 2: evaporate from the surface, will dry out more quickly, and
Speaker 2: then if the atmosphere can hold more moisture, there might
Speaker 2: be a longer time period between rain events, even if
Speaker 2: those rain events actually end up being heavier.
Speaker 1: I suppose dozens of atmospheric rivers make landfall here every year.
Speaker 1: At what point should we be concerned?
Speaker 2: I guess you've really just got to listen to what
Speaker 2: Met Service are saying, what the weather forecast is. And
Speaker 2: a lot of these atmospheric rivers are actually beneficial, right.
Speaker 2: They provide the water that we use to generate electricity.
Speaker 2: They stock up our snowfield during winter so people can
Speaker 2: go skiing. A lot of what they give us is
Speaker 2: beneficial when it gets potentially dangerous. That when Met Service
Speaker 2: will give us our weather watches or our orange or
Speaker 2: red warnings.
Speaker 4: A year ago, record rainfall hit the Upper North Island,
Speaker 4: delivering devastating flash floods at the start of the Anniversary
Speaker 4: weekend holiday. Amid the flooding and the slips, four people
Speaker 4: lost their lives, thousands abandoned their homes, resulting in about
Speaker 4: two billion dollars of insurance claims.
Speaker 1: The Auckland Anniversary floods seemed to catch everyone of God, hey,
Speaker 1: are we becoming better at predicting rainfall at all?
Speaker 2: Yeah? I mean weather forecasting in general, it improves over time.
Speaker 2: It improves as kind of people do more research, and
Speaker 2: it improves as we get bigger and better computers. There
Speaker 2: were various kind of unique characteristics. I think of that
Speaker 2: anniversary weekend blood that led to its rapid intensification, and
Speaker 2: that did catch forecasters out a little bit in terms
Speaker 2: of not being able to provide the lead in time
Speaker 2: that we might have hoped. But the contrast would be
Speaker 2: as psychoon Gabriel, which is also incredibly damaging. But we
Speaker 2: had a good idea that that was coming from more
Speaker 2: than a week out and was forecast really well by comparison.
Speaker 2: So you know, some events get really well forecast, others
Speaker 2: not quite so much. But the gradual track over time
Speaker 2: is yet that they get forecasts better and better.
Speaker 1: Thanks for joining us, Daniel. That's it for this episode
Speaker 1: of the Front Page. You can read more about today's
Speaker 1: stories and extensive news coverage at enzed Herald dot co
Speaker 1: dot nz. The Front Page is produced by Ethan Siles
Speaker 1: with sound engineer Paddy Fox. I'm Chelsea Daniels. Subscribe to
Speaker 1: The Front Page on iHeartRadio or wherever you get your podcasts,
Speaker 1: and tune in tomorrow for another look behind the headlines.