NSW floods: Rainfall records broken in the Hunter in Bulga and Cooranbong, amid La Nina and climate change effects

The Bulga weather station near Singleton recorded 377 millimetres in March.

This was the highest rainfall ever recorded at that station since records began in 1960.

The Cooranbong weather station recorded 439 millimetres in March - a record for that month since records began in 1903.

Cessnock recorded 258 millimetres in March, the second highest total for that month since records began in 1968. The record was set last year.

FORECAST: See the latest weather forecast for Newcastle and the Hunter

Dr Danielle Verdon-Kidd, a University of Newcastle climate extremes scientist, said the La Nina weather pattern was having a big effect.

"The intense rainfall we've been having is definitely connected to the fact that we've had two back-to-back La Nina years," Dr Verdon-Kidd said.

"The sea surface temperatures are warmer, there's more water evaporating and more water in the atmosphere. That's when you get bigger chances for these sorts of rainfall events."

Climate change, she said, was "compounding that".

"So for every degree of global warming, the atmosphere can hold 7 per cent more water," she said.

"More water in the atmosphere means more heavy rainfall events and a warmer atmosphere means more heavy rainfall events."

University of Newcastle Associate Professor Iftekhar Ahmed agreed that climate change was playing a part in the relentless rain.

"Yes it is climate change for sure. Climate change can happen on the La Nina natural cycles," A/Prof Ahmed said.

He said it was known that climate change produced "more frequent and intense weather".

"But there's also another side to it. It is leading to erratic and unpredictable weather patterns. It is raining at times of the year when it shouldn't be raining."

This unpredictability factor of climate change was "not often understood".

"Some places around the world which are supposed to be tropical are getting massive cold snaps. So it's all topsy turvy," he said.

He said repeated flooding in northern NSW, around areas like Lismore, was an example of the changes being experienced.

"People wouldn't have settled there, if there had been these repeat flood events. The reason why they established settlements in these areas was because it was mostly flood-free and safe."

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Dr Verdon-Kidd said it was interesting that "we've actually had three different types of rainfall systems that brought this intense rainfall".

"The Queensland/northern NSW floods from a couple of weeks ago was what's known as an atmospheric river. The Sydney floods were an east coast low.

"What we have now is another strong low pressure system."

She said climate change and La Nina "load the dice in making these systems more likely to occur".

She added that it was difficult to work out precisely "how unusual these sorts of things are, because we don't have a lot of data".

"We've only got 100 years of information. We need to look a bit further into the past, like settlers' diaries and other sources of information," she said.

"First Nations people have 65,000 years worth of history of what our climate and weather have done."

The prolonged rain being experienced in the Hunter has been compared to places like Seattle and Manchester, although those cities are much colder.

Bureau of Meteorology senior forecaster Neale Fraser said it was unusual to have so many days of rain.

"There's been no real let up because there's been no strong cold fronts coming through," he said.

"It's affecting different parts of the country. Southern states haven't had much rain. There's been beautiful sunshine in Melbourne.

"Sydney always bags Melbourne's weather but, for the last five or six weeks, Melbourne's been much better than Sydney."

Mr Fraser said moist, humid conditions with lots of showers and clouds were set to continue.

"Until we get a decent front coming through, which doesn't look likely for a while yet, it'll be more of the same," the meteorologist said.

The latest La Nina climate pattern began in November.

Heavy rain was recorded across the Hunter in that month, including 233 millimetres at Nobbys.

It was the second highest rainfall total in November for Nobbys since records began in 1862.

The Cessnock weather station recorded 231 millimetres in November. It was the first time that station recorded more than 200 millimetres in that month since records began in 1968.

A record for November was also set at the Pokolbin (Jacksons Hill) weather station, with rainfall of 219 millimetres.

In Williamtown, 214 millimetres fell in November - one of only three times rainfall had risen above 200 millimetres for that month since records began in 1942.

La Nina historically tends to break down in late summer or early autumn, but this one is expected to continue until May or June - before a return to neutral conditions.

The La Nina system had "weakened slightly" over the past fortnight".

Dr Vernon-Kidd said it wasn't certain how climate change would affect the cycle of La Nina, El Nino and neutral weather patterns.

"There is some research to indicate that climate change might enhance the cycle."

This would mean stronger La Nina events.

"Stronger La Ninas tend to have a bigger impact in Australia," she said.

Science and Technology Australia president, Professor Mark Hutchinson, said "the scale of the climate change challenge for humanity is sobering".

"The grave safety risks driven by climate change will mean more floods, bushfires, cyclones, storms and droughts on a scale never witnessed before," Mr Hutchinson said.

"Science will be our lifeline as we face all these threats - and further deep investments in Australia's transition strategy are imperative over the next year."

Mr Hutchinson added that "we need to deepen our nation's investments in discovery and translation science to meet the huge challenges before us".

"Deeper research investments are key to help us face the biggest challenge of all - the dramatic changes in our climate and extreme weather," he said.

"If Australia can be first to deliver more major science breakthroughs, it will strengthen the tools we have to help local communities through their darkest hours."

It would also help secure a stronger economy for Australia and "new jobs for our children for the long haul".

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