The wet season in Queensland has yet to begin, yet vast portions of the Australian state are under water [Reuters]

The flooding in Australia has submerged vast swathes of Queensland. What's the cause? Is it climate change or could there be something else?

Maybe it has something to do with it being a La Niña year.

Many people have heard of El Niño, as it gets blamed for crazy weather around the world, but La Niña is his lesser known sister. So what is it?

In a neutral year - which is not El Niño or La Niña - the warmer surface waters of the Pacific get blown towards Indonesia. This is due to the prevailing winds across the Pacific, and is the usual set-up.

As the warmer surface waters head west, cooler waters well up near the coast of South America. This is good news for fishermen, as these waters are full of nutrients and fish.

During an El Niño year, the set up is slightly different. The prevailing winds ease and the warmer surface waters wash back towards South America. This gives warmer than usual surface temperatures across the Pacific and cuts off the supply of cooler water near South America.

It was Peruvian fishermen who first noticed El Niño conditions centuries ago, when they tried to explain the lack of fish.

Then there is a third situation - a La Niña year - when cooler than usual waters well up near South America. These get blown westwards as the prevailing winds strengthen, and this causes cooler than usual surface waters across the Pacific.

Why do we care?

It's not just the Peruvian fishermen who should take notice, as this subtle change in the Pacific also alters the weather around the globe.

The current La Niña condition developed back in May 2010, and at that point it was clear that there was going to be some severe weather. Usual conditions include wetter-than-usual conditions in Colombia, Venezuela and Panama, and wetter than usual conditions in northern and eastern Australia.

Almost from the start of the rainy season in Colombia, it became clear that it was going to be an exceptionally wet year. The torrential rains continued until December, when even parts of Bogota became submerged.

At the end of November, Venezuela was hit by devastating floods and landslides, then just a few days later Panama was hit, forcing the closure of the Panama Canal for the first time due to bad weather.

The wet season in Queensland has not been with us for many weeks, but already vast portions of the state are still under water. The rainy season continues until March, and the La Niña set-up is supposed to continue throughout this time.

This does not mean we will have continuous flooding until March, but it does mean there is the risk of more flooding until then.

The area affected is equal to the size of Germany and France combined, and meteorologists in the area are saying that it is the worst flooding in Bundaberg since 1971 - and the highest level of the Dawson river since 1956.

It is not a coincidence that both of these years were La Niña years.

What else can we expect?

Between now and the end of February we can expect heavy rain and snow for the west coast of Canada and the US, a harsh winter in Japan, heavy rain in northern Brazil, and wet weather in the southeastern parts of Africa, including Mozambique, Madagascar, South Africa and Tanzania.

The La Niña conditions are expected to ease between April and July, and after that maybe the weather will have the chance to calm down.

Source: Al Jazeera