Climate change and La Nina: Parts of Australia are getting flooded – Knowledge

House roofs just above the water’s surface are washed away, miles away from cattle farms: large areas of southern and eastern Australia are currently flooded. Flood warnings are currently in effect for five of the eight states and territories. The Murray River, Australia’s longest river, has recorded new highs in Victoria, flooding towns, villages and farmland beyond its banks, which could push up food prices further.

More than a third of all government departments in the state of New South Wales declared a state of disaster in October. Tens of thousands of people living in Lismore, on the east coast, were again told to leave the city last weekend. Many of them were in the process of rebuilding their homes as the city of 44,000 was flooded only twice, in February and March. To their relief, the water level this week was below the feared level – at least this time.

The last three consecutive La Niña years were 21 years ago

A trigger for the heavy rains that have hit the Red Continent since the start of the year is La Nina, a weather phenomenon that always sets the pace in and around the Pacific. During La Niña periods, unusually strong trade winds blow across the tropical Pacific, driving warm ocean surface water across the ocean from the west coast of South America to Southeast Asia and the east coast of Australia. The eastern Pacific is colder than usual because of increased flow of cold water from the depths, resulting in reduced wind currents and drier weather. However, in the west, the water is warmer, the winds rise and bring more precipitation to the land.

La Niña’s twin, El Niño, has the opposite effect: surface winds over the tropical Pacific are weaker than usual. It rains in Peru, while Australia basks in the sun under cloudless skies and the water warms. Major coral bleaching occurs during an El Niño year—though not always.

Anticlimatic conditions oscillate back and forth every three to seven years on average. This phenomenon is known as El Niño Southern Oscillation or ENSO for short. Normally, La Niñas last only a year or two, but this year was the third in a row. Such “triple dip La Niña” was last recorded in 1973-1976 and 1998-2001. The longer a La Niña event lasts, the more impact there will be as river basins are already full. Even if it rains a little then the flood will overflow.

Australian science organization CSIRO expects climate change-induced extreme La Niña events to become more frequent this century. The average temperature in Australia increased by about 1.47 degrees Celsius between 1910 and 2020. “The frequency of extreme La Niña events will increase from one event every 23 years from 1900 to 1999 to one event every 13 years from 2000 to 2099,” said CSIRO’s Wenju Cai. “More El Niño events favor the development of more intense La Niña events, so we can expect frequent swings between opposite extremes from one year to the next.”

All rain makes everything green – but it also brings danger

Measurements of water surface temperatures in different parts of the Pacific offer insights into the future: the International Institute for Climate and Society thinks there is a 75 percent chance of La Niña continuing through the austral summer (December to February). ).

“With rivers and dams already full and catchments wet, any rain in eastern Australia could cause widespread flooding,” the Australian Bureau of Meteorology warned. In addition, there is an unusual number of cyclones in the north of the continent, the first of which may hit the country in early November.

At the edge of the flood plains, forests and meadows are green today as the wet spring stimulates growth everywhere. For many Australians the scene is ringing further alarm bells. For what too much vegetation can do has been known since the terrible days of the “Black Summer,” when large parts of Australia were engulfed in flames.