AI reveals how a warming climate will intensify NZ’s most extreme downpours

Fiona Goodall/Getty Images The most damaging weather events are the record-breaking “one-in-100-year” disasters communities have usually only seen once.

But understanding how these rare events could change in the future is hard.

With few examples in historical records, it is difficult to estimate how severe they could become and how outcomes might vary across possible futures.

Recent research shows the weather systems bringing heavy rain to New Zealand each year are expected to become more intense as the climate warms.

In our new study , we used generative artificial intelligence (genAI) to simulate hundreds of ways this century might unfold and to explore how extreme rainfall might change across these possible futures.

We know that a warmer atmosphere can hold more water vapour, allowing storms to produce heavier rainfall.

But much of our understanding comes from global models whose grids are so coarse that entire region, such as Auckland, can fall within a single grid cell.

By using genAI to explore these changes at finer scales across New Zealand, we found the rarest downpours become more intense as the planet warms, with larger increases than for the heavy rainfall we experience more often.

In a future where greenhouse gas emissions keep rising, the amount of rain falling per day in a one-in-100-year event increased by about 9% per degree of warming, averaged across New Zealand and the possible futures we simulated.

For the heavy rainfall we experience more often, the increase was about 5.6% per degree.

The heavier the daily downpour, the greater the potential for flooding and damage.

A one-in-100-year event means there is a 1% chance of rainfall exceeding record amounts in any year.

But these events do not happen neatly once a century.

They can happen close together, and their odds change as the climate warms.