Scientists ‘move’ New Zealand into historical cyclones to model impact
Met Office scientist Dr Ian Boutle has been working with NIWA in New Zealand on modelling weather events for the country’s contingency planners. The below blog highlights how they took on the challenge in an unusual way.
Tropical cyclones don’t tend to directly impact on New Zealand. So, when scientists from the Met Office and NIWA (New Zealand’s National Institute of Water and Atmospheric Research) were asked to model potential impacts from cyclones on the country, it was a problem that needed some creative thinking. Their unique answer? Simply ‘move’ the land into the path of historical storms – metaphorically speaking.
By the time tropical cyclones reach New Zealand’s latitudes, they have already undergone a transition into extra-tropical cyclones. These tend to be a bit weaker than the tropical cyclone they derived from, but they can still pack a heavy punch and there is a history of ex-tropical cyclones impacting on the country, hence the need for this project to see potential impacts from a stronger storm getting to the country.
The research is part of New Zealand’s mitigation and adaptation planning for the future and the data provided by the simulations is now being worked on by New Zealand contingency planners to see how infrastructure in Auckland, New Zealand’s most populous city but one that has historically escaped the worst impacts of previous ex-tropical cyclones, would cope with these impactful weather events. Modelling weather events in this way provides contingency planners with reliable data, even when there’s little history of such impactful weather hitting the region.
Met Office Scientific Manager Dr Ian Boutle, who worked with NIWA as part of a secondment, said, “Historically, New Zealand doesn’t get affected by fully-fledged tropical cyclones but a changing climate means that it’s something that’s possible in the future, as warmer sea surface temperatures wouldn’t weaken these cyclones as much as they travel south.”
Climate change is just one reason behind the research. City planners, flood experts and scientists are currently working through the data provided by NIWA to see how the country would cope in the face of direct impact from an ex-tropical cyclone, including investigating the potential for landslides, flooding and building damage.
Shifting into real weather
The requirement for modelling these different realistic scenarios created an opportunity for the scientists to consider how to model the most realistic weather events for the country. The answer, of course, was to use real weather events.
“Historically for New Zealand, there’s not much to go on in terms of active cyclones making landfall,” explained Dr Boutle.
“One idea is to create an atmospheric state inside the Met Office’s Unified Model to create a cyclone that follows the path you want and go from there. However, that’s very tricky to do within the model and raises questions as to what would be a realistic cyclone coming at New Zealand from the tropics.
“What turned out to be much easier and more effective to do was to look at recent ex-tropical cyclones that have passed close to New Zealand, and simply pick up and shift the landmass into its path and let the simulations show how the cyclone would behave and develop if it did hit land.”
This map, as captured from the research, shows the north of New Zealand being affected by Tropical Cyclone Cook
In order to lessen the impacts of sea temperatures being warmer further north, scientists only shifted New Zealand on the east-west axis. With New Zealand in its ‘new’ location, the Met Office Unified Model ran the simulations for the weather set up, but this time taking in to account the impact of the new landmass and developed the weather system differently.
This meant NIWA could provide the New Zealand government with realistic scenarios, as it was a real weather event in the vicinity of the country. Model runs were done for five different cyclones, shifting New Zealand into the path of each one to provide a number of scenarios for the planners to analyse.
“When we move the landmass in to the path of a cyclone we already know has happened, what it does is develop the system in a different way once it hits land instead of sea. In short, cyclones evolve differently over land and the model reflects that and provides realistic data for us on wind speed, rainfall amounts and trajectory,” said Dr Boutle.
“What we found is that by introducing land to these historical events, wind speeds obviously drop when land is reached, but New Zealand’s northern city of Auckland is right on the coast and so impacts from wind were more severe here. In terms of rainfall amounts, this could change either way when we introduced the new landmass, with some model runs giving higher levels of rain and some producing less than if it didn’t hit land.”
Proof of concept and climate change
The research, published with NIWA colleagues Stuart Moore and Richard Turner, plays an important role for New Zealand’s planning going forward, but it also acts as a proof of concept for other scientists researching in similar areas.
Dr Boutle concluded: “With the rise in global temperatures we’ve seen since the industrial revolution, it’s possible for cyclones to move differently in the future, using a warmer sea surface temperature to retain strength and this increases up the possibility of new routes. Modelling in the way we have opens new possible research into potential impacts of these long-term climate changes.”
Original article link: https://blog.metoffice.gov.uk/2022/02/02/scientists-move-new-zealand-into-historical-cyclones-to-model-impact/
Latest News from
Do you know what climate action to take for a safer future?24/03/2023 15:10:00
The science is clear, the climate is changing. The Met Office is one of the UK’s foremost climate change research centres, carrying out world-leading research.
Over half of public making low-carbon decisions22/03/2023 14:15:00
Polling by the Met Office shows that over half the British public are consciously making low-carbon choices, with nearly two thirds wanting to do more.
Reducing odds to limit warming to 1.5°C rise21/03/2023 12:15:00
Aspirations of halving global emissions by 2030 would only deliver a 50:50 chance of keeping the most ambitious pledge of the Paris Agreement alive, says the Met Office.
Mixed week of rain, wind and snow14/03/2023 15:25:00
This week will see unsettled weather for many. There will be some snow and ice at first, mainly in the north, but conditions will turn milder later in the week.
A brief respite for some before cold returns10/03/2023 16:25:00
Wintry conditions will be slowly easing their grip on most parts of the UK over the weekend, but a return to colder conditions for many is likely in the early part of next week.
Has it been an unusually cold start to March?09/03/2023 13:15:00
March heralds the start of Meteorological Spring, and with daffodils, snowdrops and crocuses making an appearance many of us start to think of warmer sunshine and longer days.
Amber warning for snow09/03/2023 11:05:00
An Amber warning for snow has been issued for central and northern England.
New research shows increasing frequency of extreme rain08/03/2023 15:15:00
Extreme rainfall events could be four times as frequent by 2080 compared to 1980s.