An Azeri helicopter carries water before releasing it over a forest fire near the settlement of Kustarevka in Russia.

An Azeri helicopter carries water before releasing it over a forest fire near the settlement of Kustarevka in Russia. Photo: Reuters

The devastating Russian heatwave and Pakistan floods are caused by one unusual weather pattern - the static jet stream, meteorologists say.

The northern hemisphere jet stream, a fast-moving high-altitude air current, circles the earth from west to east.

But in the past month, a "blocking event" has brought the jet stream to a halt, keeping weather patterns stationary over certain countries.

A US helicopter takes supplies to flood victims in Kalam, Pakistan.

A US helicopter takes supplies to flood victims in Kalam, Pakistan. Photo: AP

"Over Pakistan, the weather pattern is just staying with the monsoon, and the monsoon is bringing drenching rains," weatherzone.com.au meteorologist Josh Fisher said.

"But this jet stream is also bringing dry air from eastern Africa right up into Russia and this continuous heatwave is allowing the wildfires to build."

Australia is not caught up in this rare phenomenon, as the southern hemisphere has a separate jet stream based around the south pole, Mr Fisher said.

The effects of the stalled jet stream across Europe and the US have been catastrophic.

In early July in the eastern states of the US and Canada, a heatwave caused numerous deaths and power cuts.

In Pakistan, about 1600 people have died since floods struck in July and early August, while about 14 million are struggling to cope with the consequences of the natural disaster, the UN and Pakistani government said.

In Russia, an unprecedented heatwave has triggered about 557 wildfires and left the capital Moscow cloaked in heavy smog. Moscow's daily mortality rate has doubled to about 700, the city's health department head said, with city morgues almost full.

Mr Fisher said the Rossby waves - spinning wind currents that give the jet stream its wavy form by pushing it north and south - are responsible for the stalled jet stream.

The waves have been stronger this year, working against the jet stream and bringing it to a halt.

This blocking pattern, while difficult to predict, usually lasts about eight to 11 days, he said.

"The one that brought the hot temperatures to the US lasted over a week, while the current one affecting Pakistan and Russia has been persisting for already around eight days and could last for a few more days."

But less is known about what triggers this abnormal activity.

Climate change has been cited as one possibility, but scientist Gerald Meehl of the National Centre for Atmospheric Research in Colorado told the New Scientist magazine there was no way to test the theory, as the resolution in climate change models was too low to replicate weather patterns such as blocking events.

Another cause could be low solar activity, Mr Fisher said.

Low solar activity has already been linked to an increase in cold winters in Europe, with activity on the sun declining since 1985, Professor Mike Lockwood of the University of Reading said in findings published in April.

Mr Fisher said "heat sources such as surface heating and cooling can [also] have an affect on these blocking events".

There are no current indications that any similar patterns are set to affect Australia, Mr Fisher said.

The planet has never been as hot as it has been in the first half of this year, the US National Oceanic and Atmospheric Administration said in a July report.

According to the Intergovernmental Panel on Climate Change (IPCC), which has tracked the impact of human activity on climate for the past 20 years, droughts and heatwaves likes those affecting Russia and 18 US states become longer and more intense in a warming planet.

"Whether in frequency or intensity, virtually every year has broken records, and sometimes several times in a week," said Omar Baddour, who tracks climate change for the World Meteorological Organisation.

"In Russia, the record temperature in Moscow [38.2 degrees in late July] - which had not been seen since records began 130 years ago - was broken again at the start of August. In Pakistan, the magnitude of the floods is unheard of," he said.

- with AFP

Weatherzone.com.au is owned by Fairfax Media.