Farmers need to adapt for a drier future as once-in-a-lifetime events like the North Island drought become closer to the norm, a top climate scientist warns.

James Renwick, Associate professor of physical geography at Victoria University, said global warming was the only explanation for the current drought, which he described as "an exceptional event".

"It's probably the first time in 50 years that it's been this dry over this much of the country," he told TVNZ's Q+A programme today.

He warned conditions as dry as this summer's would become more common, as average temperatures increased due to climate change.


A dry summer now would be closer to the norm in 50 to 100 years' time, while a one-in-50 year event like the current drought would be a one-in-20 to one-in-25 year event by the middle of the century.

"And in some parts of the country, it might be a one-in-five year event by the end of the century, which means the farming sector's going to have to adapt to that.

"We've got time. It's decades we're talking about, and farmers are very adaptable, but things will have to change."

Dr Renwick said farmers would have to move away from intensive farming towards more sustainable, lower intensity farming with lower stocking rates.

"The present intensification of farming and dairying, in particular, doesn't look very sustainable, given the way the climate's likely to change."

Dr Renwick said storing more water and using it more efficiently would also help.

"That counts for a lot. Winter times are not likely to become drier, so I think it's going to come down to storing the water when it falls or when it flows in the rivers, and using it."

Dr Renwick said the Ministry for Primary Industries had put out clear messages about how farmers could adapt to the changing climate this century.


But some farming groups were adapting more than others, and change was happening "in a patchwork kind of way."

Dr Renwick said the Government needed to do more.

"It is an incredibly big issue. It's the biggest issue," he said.

"I think the Government does have policy around adaptation, but I think there could be more political leadership on this issue."