Historically, extreme weather events have caused significant damage, disruption and financial cost. In 2013 and 2014, two windstorms contributed to insured property losses of around $250 million. The Insurance Council predicts these values will increase with the effects of our increasing population and climate change.
Funded through the Ministry of Business, Innovation and Employment’s Natural Hazards Research Platform, researchers from the consortium harnessed the power of NIWA’s supercomputer and the New Zealand Convective Scale Model (NZCSM) to better understand wind speeds that structures are designed to withstand and get a handle on damages wrought by wind.
Using a technique known as predictive modelling, the team pored through decades of wind speed data and simulated the path of previous damaging windstorm events in Greymouth and Canterbury.
WSP technical principal Peter Cenek says by analysing past weather events like these, we’re able to better predict the trajectory of future events.
“Replaying the storms numerically meant we could compare where the damage happened with where the model said the highest wind speeds were going to occur. The correlation was surprisingly good - giving us confidence that the model could be applied more widely across New Zealand.”
Data from the consortium’s modelling has now been included in the latest update to the Australia and New Zealand wind loadings standards, which features regional estimates of the strongest wind gusts structures are likely to experience. Getting the numbers right means New Zealand’s buildings and infrastructure have the right levels of structural safety and performance.
WSP researcher Neil Jamieson says relying just on historical wind speed data to inform design standards and understand where damage is likely to happen is a problem. There are only so many weather stations, many of which are sited at airports.
“The whole of the Wellington region has the same design wind speed. But the design speed on the flat is completely different to elevated locations in complex terrain. The beauty of using the NZCSM is its 1.5-kilometre resolution – meaning we can better understand the influence of wind at more exposed sites and look at whether there are design savings that can be made in less-exposed areas.”
The Australia / New Zealand standards don’t yet have that level of detail, but the hope is that one day a clickable online map is created to work out exactly what the design wind speed should be at specific locations, rather than regionally.
While the chances of a building breaking in the wind are slim, there’s lot of benefits in taking such a detailed numerical approach to understanding the influence of wind speeds in our changing climate.
WSP principal research engineer Nick Locke says knowing more about where and when extreme windstorm events are more likely to occur can help minimise infrastructure shutdowns like that experienced on the Auckland Harbour Bridge in 2020 when gusts toppled a truck.
Plus, improving our knowledge of design wind speeds can help emergency services prepare in advance for damaging weather events, act as a reminder for homeowners to keep up with home maintenance, and spur builders and developers to use high quality fixings.
The consortium is now using the same numerical modelling approach to better understand the influence of snow and ice loading on high voltage transmission towers. It’s also working with the Building Research Association of New Zealand - stress testing the Building Code to see how it would cope if wind levels increased by five, ten or even fifteen percent.
