Every drought is different, but when it comes to the current drought conditions across the Murray-Darling Basin, BOM says it is now "the most severe in 120 years of records".

Key points: Climatologists say that the Federation drought (1891-1903) and the World War II drought were similar to current conditions

Climatologists say that the Federation drought (1891-1903) and the World War II drought were similar to current conditions Not everywhere across the Murray-Darling is experiencing its record-worst drought conditions

Not everywhere across the Murray-Darling is experiencing its record-worst drought conditions Just to provide relief, not even to break the drought, BOM says some places would need record high rainfall over the next three months

In a presentation on Thursday, climatologist at the Bureau of Meteorology, Dr David Jones, said that the Federation drought (1891-1903) and the World War II drought were similar to this one.

"The general picture across the Murray-Darling Basin, for droughts lasting two to three years, this is the most severe we've now seen in terms of the rainfall totals and probably also in terms of the general runoff into dams," he said.

The variable nature of droughts makes them hard to compare as everyone experiences drought differently, and not everywhere is currently experiencing its worst drought.

Conditions in the southern basin are significantly less severe than in the north.

"If you look in southern Victoria, for example, the stand-out drought is clearly still the Millennium drought," Dr Jones said.

Going back further into the paleo record there have been bad droughts, but Dr Jones said you could not really compare those prehistorical droughts.

"Certainly this is about as bad as it has got in our records. It is pretty severe," he said.

Over the last two years rainfall has been below average for much of the country. ( Supplied: Bureau of Meteorology )

What is making this drought so bad?

Dr Jones outlined three main reasons:

1. Warm conditions in the far Indian and Pacific Oceans resulting in reduced rainfall 2. Underlying reduction in southern wet season rainfall 3. Underlying temperature increase

Both the Pacific and Indian Oceans have been unhelpful to our rainfall, according to Dr Jones.

These climate drivers are not the only way for drought to come to Australia, but they are commonly associated. They can also work to complement or counteract each other. ( ABC Weather: Kate Doyle )

"While we haven't quite hit the mark for an El Nino declaration we've been very close, and we have been very close for a long time.

"The Indian Ocean continues to be so, we are currently on the verge of a positive Indian Ocean Dipole event."

Over the past few decades, southern cool season rainfall has been declining.

"Certainly there is significant variability in our climate system but it does appear, as we might have expected, that cool season drying in southern Australia is probably exacerbating the drought in some areas," Dr Jones said.

This excerpt from the State of the Climate Report 2018 shows winter rainfall over southern Australia has been declining over the past 20 years. ( Supplied: CSIRO and Bureau of Meteorology )

On top of that, it has been hot.

Due to climate change, mean temperatures in Australia have gone up by just over one degree Celsius since the BOM started keeping records in 1910.

"That means this drought is a bit different. What we've seen in the past doesn't necessarily apply to droughts in the present," he said.

Increased temperatures can increase evaporation, drying out soils.

Plus it can mean livestock need more water to keep cool, further exacerbating water storage issues.

"We also know high temperatures add to the drought stress. Plants, for example, if it's dry it's bad. If it's hot and dry it's worse," he said.

How much rain will it take to break this drought?

If you are looking for a happy ending this would be a good time to go read something else.

To ease the conditions, but not even break the drought, Dr Jones said "we need to get, in some places, record high rainfall for the next three months — just to provide some measure of relief".

"Unfortunately, for a lot of Australia, in the next three months it's not the time of year that droughts are likely to break."

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The current outlook is not good. There will still likely be rain, but the chance of the heavy, widespread, drought-breaking rain in the next three months is slim.

"We know the spring tends to be quite dry," Dr Jones said.