Blocked breezes

Weather conditions around the world have taken on a extreme nature recently as fires burn through Russia and floods in Pakistan have millions fighting for their lives. Meteorologists are still scratching their heads when it comes to explaining the causes of recent global weather disasters.

"In Moscow the record has been broken 22 times, Pakistan was associated with enormously high precipitation," the World Climate Research Program’s Vladimir Ryabinin said from Geneva. "This is a question on which several meteorological services are working. It is difficult to say exactly what the reasons are. We are, unfortunately, speculating a little bit."

Typically, air currents above Asia and eastern Europe blow from west to east, but a high pressure system has blocked circulation this summer, and that's forced the jet stream to move further south, according to the Met Office, Britain's weather service.

Blocked streams

By moving south, the cold air of the polar jet stream does not aid circulation over Russia and hits the warmer air the northern hemisphere's subtropical jet causing severe storms in southern Asia.

"Because of the situation in Russia, there was a reduced possibility for the air to leave the region where the enormous precipitation took place," Ryabinin said. "It was blocked from one side by the Himalayan Mountains and on the other side by the weather pattern that formed in Russia."

The ongoing La Nina phenomenon is also providing favorable conditions for heavy rains in Asia. The counterpart to El Nino, La Nina cools water temperatures in the Pacific Ocean of the coast of South America warms Asian waters.

"La Nina tends to be associated with more precipitation in India," Ryabinin said. "There are higher temperatures than usual in the Indian Ocean, and this affects humidity of air masses that are travelling to India with monsoon winds."

More storms brewing

Violent swings in global weather patterns, including the reoccurrence of extreme events meteorologists would expect to happen only every 100 years, are likely to become more frequent, as predicted by a 2007 report by the UN Intergovernmental Panel on Climate Change.

"The IPCC report in 2007 indicated the possibility of more frequent and intense extreme climate events and I think what we see is in line with the projections," Ryabinin said.

Harsher monsoons, like the one currently being witnessed in Pakistan, are also likely to worsen with time and climate change, according to Andres Levermann from the Potsdam Institute for Climate Impact Research.

"We are expecting heavier monsoons due to climate change - all the models show that," he told Deutsche Welle. "There are serious problems with increasing amounts of rainfall. There are times when it just doesn't stop raining."

Asian epicenter

Asian nations will be particularly hard hit by changing weather events according to Peter Hoeppe, head of Munich Re's Geo Risks Research Unit. Munich Re, the world's largest reinsurer, maintains a database that tracks natural catastrophes and the damage they cause.

"The database shows that Asia has experienced the highest increase in the number and intensity of natural catastrophes," he told Deutsche Welle.

Even as Russia's fires smolder and Pakistan's rain abate, scientists will be meeting in France and the US to try to determine what may have caused this summer's extreme weather conditions - and to discuss more accurate ways to predict them in the future.

Author: Volker Mrasek (sms)

Editor: Stuart Tiffen