Three maps that reveal NZ’s climate future

Analysis: New climate projections from Niwa offer for the first time an extremely local look at how New Zealand’s temperature and weather patterns may change as the world continues to warm.
The new data forecasts average temperatures, number of hot days, rainfall, wind and growing degree days, among other variables, for a wide range of future dates and climate scenarios in five-by-five kilometre blocks. In total, there are almost 11,500 blocks with dozens of climate projections.
Researchers used a supercomputer to scale comprehensive climate models from the Intergovernmental Panel on Climate Change (IPCC) down to the local level.
“Niwa’s supercomputer ran hot for 12 months to downscale the global data. The computing power needed is equivalent to running more than 150 high end laptops non-stop for a year,” says Andrew Tait, the Crown research institute’s chief scientist for climate, atmosphere and hazards.
The data was produced to inform councils about expected hazards, as well as iwi and other community stakeholders and businesses which may be making investment decisions. However, it is publicly accessible as well, in the form of an interactive map and dashboard hosted by the Ministry for the Environment and raw data published by Niwa.
Newsroom has combed through Niwa’s data to produce three sets of maps showing New Zealand’s climate future, at three different snapshots of this century: 2021 to 2040, 2041 to 2060 and 2080 to 2099.
While New Zealand, like the rest of the world, will grow hotter under climate change, this won’t be evenly distributed across the country. Extreme weather – in this case the number of days where temperatures exceed a set level – is even more irregular.
Mountainous areas in the country are less likely to be affected. The Wellington region, due in part to upwelling of cold coastal waters, doesn’t see a large change in the number of hot days.
Other populated regions, including Auckland, Hamilton and Christchurch, will see significant increases in the number of hot days they see a year. By the end of the century, Auckland will experience another 50 days where temperatures exceed 25 degrees every year – nearly two more months.
Looking beyond the averages is important, because a degree or two of increased average temperatures isn’t noticeable but a significant change in the frequency of extreme weather is. People will experience climate change in the extremes, not in the average.
While New Zealand won’t warm uniformly, it will grow hotter everywhere. Rainfall is a different story.
Niwa’s data and Newsroom’s analysis suggests some regions will see significant increases in total rainfall (peaking at plus 16 percent a year in Queenstown at the end of the century) while others will see significant decreases (minus 14 percent in Kaikōura at the same period).
Overall, the south and west of the South Island as well as the Wellington region will see increases in total rainfall over the year, while the east coast of the South Island and the rest of the North Island will get drier.
While this pattern has been predicted before, the new findings lean slightly drier across the board than expected – so the wet areas get less wet and the dry areas get even drier than previously forecast.
There is not as much regional differentiation in the change in average daily air temperature across the country, but this map is perhaps the most important one.
Niwa’s modelling produced results for three different climate scenarios constructed by the IPCC: a low-emissions pathway, a middle-of-the-road pathway and a high-emissions path.
Newsroom has used the middle-of-the-road pathway, called Shared Socioeconomic Pathway 2-4.5, for the previous charts in this article. This scenario is considered the closest one to the pathway sketched out by global climate policies at the moment and would lead to between 2 and 3.5 degrees of warming by the end of the century.
The higher-emissions scenario, pathway 3-7.0, is considered unlikely to occur by the IPCC. It would require backtracking on climate policies, although this has happened in some countries in recent years – including in New Zealand.
Nonetheless, if the world did follow this pathway, it would lead to global warming above preindustrial levels of between 3 and 4.5 degrees by 2100.
In New Zealand, as the below maps show, parts of the country could reach 5 degrees above the 1986 to 2005 average – which itself was warmer than preindustrial levels.
But this doesn’t have to be New Zealand’s fate – nor does the middle-of-the-road scenario which still leads to more than 3 degrees of warming in much of the country.
Pathway 1-2.6 shows what would happen if countries acted fast to cut emissions drastically, in an effort to limit warming to 1.5C. While there might be some temporary overshoot, this pathway would likely reduce temperatures to below 1.5C above the preindustrial average by the end of the century.
New Zealand, too, would be better off.
Under this path, some parts of the country would actually be cooler in the last two decades of the 21st century than in the middle of it. Globally, emissions and temperatures would be trending in the same direction – and New Zealand would benefit too.
Which pathway we end up on is ultimately up to us.