Study debunks claims of ‘worsening extreme rainfall’ in New Zealand

A University of Waikato study has been cited by investigative journalist Ian Wishart as evidence that New Zealand’s historical rainfall record does not support claims by legacy media that extreme rainfall events are becoming more frequent or more severe.

In a series of social media posts, Wishart pointed to research by Sigid and colleagues published in 2025, arguing the study’s maps of New Zealand’s most extreme rainfall events show the opposite trend to that commonly presented in public debate. According to Wishart, the research indicates the country’s most intense rainfall events were substantially more frequent during the early 20th century than they have been in the 21st century.

Wishart said the study shows the period from 1921 to 1940 experienced a far greater concentration of the nation’s most extreme rainfall events than recent decades, with every point on the maps representing one of New Zealand’s highest recorded rainstorms.

He argued the findings directly contradict repeated claims that climate change is already causing heavier and more frequent rainfall across New Zealand.

While climate models project future increases in extreme rainfall under a warmer climate, Wishart said those projections are based on the modern rainfall record and still fall well short of the concentration of major storms shown in the historical data from the early 1900s.

“The climate change era of the 21st century has been a walk in the park by comparison,” Wishart wrote, arguing New Zealand has become less resilient despite earlier generations facing more severe weather.

The posts come as Wishart continues High Court proceedings against TVNZ, TV3, RNZ and the Broadcasting Standards Authority over what he alleges is inaccurate and misleading reporting on climate change and extreme weather.

Wishart says the legal action is not intended to challenge climate change itself, but the standard of journalism surrounding it. One of his complaints relates to media reports describing a 24-hour rainfall total of 130.8mm at Dunedin’s Musselburgh rain gauge in October 2024 as the city’s “wettest day in over a century.”

He argues historical records show significantly larger rainfall events in 1923, 1929, 1968, 1980 and 2015, and contends the Broadcasting Standards Authority failed to properly consider that evidence when rejecting his complaint.

Wishart also argues that declining public trust in New Zealand’s legacy mainstream media reflects a broader failure by broadcasters and regulators to rigorously test factual claims on climate-related issues, saying his court action seeks greater accountability and higher journalistic standards.

The Weekend Read: Three images from a Waikato University extreme rainfall study tell the real story of the extreme weather trend.

Every earnest climate activist clutching their well-thumbed instruction manual, Climate Change For Dummies, needs to study these images and let them… pic.twitter.com/P8DiblsZce

— Ian Wishart (@investigatemag) July 10, 2026