Why is Queensland flooded?

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BBC Meteorologist Nina Ridge explains La Niña

Australian officials say Queensland is reeling from its worst natural disaster in history, after floods have caused billions of dollars worth of damage.

So why has there been so much rain along eastern board of Australia? BBC Meteorologist, Nina Ridge, says the persistent rainfall has been the result of a weather phenomenon called La Niña.

La Niña is a weather pattern that affects the Pacific Ocean region, and occurs when surface sea temperatures are cooler than normal in the eastern Pacific, and warmer than normal in the western Pacific.

The flooded main street in Rockhampton's city centre

Normal conditions

Normally, cold water comes up from the deep sea and pools near the coast of South America.

Easterly trade winds drag the cold water from South America across the Pacific towards Australia. The cold water is gradually warmed by the sun as it reaches Australia.

Rain clouds build along the coast of Australia due to the warm moist air, while it tends to stay dry along the Pacific coast of South America.

La Niña

During La Niña, the cold water that pools near the coast of South America surges across the Pacific and there is a greater build up of warmer water along the eastern coast of Australia.

As a result, there is a greater contrast in sea surface temperatures between the east and west Pacific, and a greater contrast in air pressure.

The easterly trade winds become stronger due to this contrast, dragging warm, moist air along the Australian coastline, creating larger rain clouds and producing more rainfall.

An El Niño weather event is when warm water pushes towards the central Pacific, the cold water retreats and rain falls in the central Pacific area. Strong El Niño years can cause droughts along the eastern coast of Australia.