PARCHED: Waikato pastures are dry, like the hills around Scotsman valley. Drought has been declared in the region.

Drought gripping the North Island is the most severe in history, with the crisis far from over both for now and in years to come, scientists say.

Long, dry spells are forecast to double by 2040 as temperatures continue to rise and New Zealand heads towards a more Mediterranean climate.

Experts warn it could spell the end for farming as we know it and may cost the country billions of dollars in drought relief each year before practices are adjusted.

"This is historic," said climate scientist Jim Salinger, who has calculated that the amount of rain needed for grass growth was the highest since records began. "It's like comparing your income against expenditure in your cheque book. And we are in deficit."

Drought was declared last week in Northland, South Auckland, Waikato, Bay of Plenty, Coromandel and Hawke's Bay, meaning extra government funding is available for hardship.

Another two regions, Manawatu and Rangitikei, have asked the Government to declare a state of drought in their regions, which could come as early as Wednesday.

Yesterday, a near total fire ban was declared across the North Island, also for the first time.

It was equally dry in parts of the south, though it is forecast to rain lightly in Canterbury this week.

Hokitika cattle farmer Kees van Beek said if the dry weather continued on the West Coast for another fortnight, things would become "fairly desperate".

Van Beek, who has farmed in the area for more than 40 years, said while there were some very dry summers back in the 1970s, this summer was "as dry if not drier".

His property had seen just 8mm of rain in the last 30 days. "We normally average 11mm per day throughout the year."

In the heartland of the Canterbury plains, they are used to big dry summers.

"Hot dry weather is actually quite good for growing grass," said dairy farmer James Bourke in Culverden. Then comes the laconic kicker. "When there's water. It's just that when there's no water it's not so good.

"The river levels are so low and the ground water is quite low, so even irrigation is starting to disappear. The Waiau is still good. There's reasonable flow and it's not on restriction.

"The other half of Culverden is using the Hurunui irrigation scheme and they have no irrigation because of restrictions and the grass is burning off because it's so dry.

"They're going through a lot of supplement. The price of supplement is going up and palm kernels are getting expensive."

In Cheviot, Hamish Haugh runs sheep. While it was drier than what he would like to be, it was not yet a drought. Not yet.

His eyes are on the horizon though, hunting for rain clouds. He wants some rain in the next 10 days.

"In Canterbury we're generally used to having droughts more often. We have a significantly dry year one out of five.

"We are always conservative with our stock numbers and we always keep supplements on hand."

Salinger said the regional spread of the drought was more extensive than in any of the past 70 years, taking in most of the North Island.

Severity of drought is measured by potential soil moisture deficit - the amount of water that would be required to keep pastures topped up with moisture for grass growth. Already, the North Island requires 362mm of rain to keep the grass growing. Previously, the highest record rainfall needed was in the summer of 1945-46 when the deficit was 361mm.

Salinger's calculation sits alongside data released by Niwa last week showing that drought will only become more intense and more frequent in the next 30 years.

DROUGHT FACTS

Who's affected?

Parts of the North Island have received between a third and a half of the normal rainfall levels over summer. The following areas have been officially declared to be in drought:

■ Northland.

■ South Auckland.

■ Waikato (including Coromandel, Hauraki and Matamata-Piako).

■ Hawke's Bay.

■ Bay of Plenty.

Manawatu and Rangitikei have asked the Government to declare a drought in their regions.

What is it costing?

■ DairyNZ estimates that by the end of March, milk production for 2013 will have been reduced by 260 million litres - representing lost income of around $130m.

■ The average Waikato dairy farmer will lose an estimated $140,000 in lost revenues and increased expense.

■ The Government says total losses to the economy could reach $1 billion.

The history of drought - and the future

■ 2007 - Record low rainfall in many northern and eastern areas leads to a shortage of feed and lower than normal spring lambing and beef numbers.

■ 2008 - Waikato experiences driest January in a century. Severe moisture deficits continue in North Island until April/May, with the estimated cost to agriculture exceeding $1b, and an 11 per cent fall in sheep numbers.

■ 2010 - 253mm of rain falls in Northland between November 2009 and April 2010, leading to its worst drought in 60 years. In the previous year 748mm of rain fell.

■ 2050 - Niwa models suggest that by mid-century, farmers in most North Island regions, as well as those in eastern regions of the South Island will be spending 5 to 10 per cent more of the year in drought.

What can farmers do?

■ Build more dams.

■ Plant trees as feed.

■ Change stock mix.

■ Improve irrigation

■ Leave grass longer.

FUTURE FEARS

The Ministry of Environment warns climate change will bring more drought to some areas, especially Waikato, Wairarapa and Marlborough over the rest of the century.

Here's a summary of predictions based on climate change modelling:

Northland: Decreased annual rainfall but more intense, heavy winter rain.

Auckland: Time spent in drought ranges from minimal change through to more than double.

Waikato: Time spent in drought is likely to increase, leading to water shortages and wild fires.

Bay of Plenty: Spring rainfall is likely to decrease by 9 per cent.

Gisborne and Hawke's Bay: Winter rainfall is likely to be down by 16 per cent.

Taranaki: Little change to annual rainfall, winter rainfall down 6 per cent.

Manawatu and Whanganui: Very heavy rainfall likely to be more frequent.

Wellington and Wairarapa: Much less winter and spring rain. Time in drought likely to increase.

Marlborough: Time in drought likely to increase.

Nelson: Annual rainfall up 4 per cent.

Canterbury: Winter rainfall down 11 per cent in Christchurch, up 18 per cent in Tekapo.

West Coast: Wetter; heavy rainfall events more frequent.

Otago: Rainfall up 4 per cent in Dunedin, rainfall up 12 per cent in Queenstown.

Southland: 7 per cent more rain, more in winter.

Other warnings include:

Heat: Higher temperatures will mean an increase in demand for air-conditioning systems and therefore for electricity in summer. But there will be a reduction in demand for winter heating.

Flooding: More frequent intense winter rainfalls to increase the flooding by rivers, as well as flash flooding when urban drainage systems become overwhelmed.

Water: Water demand up during hot, dry summers. Lower river flows in summer will aggravate water quality problems.

Source: Ministry of Environment