Climate change and La Niña: half of Australia sinks into the floods – knowledge

House roofs just above the surface of the water, livestock washed miles away from the farms: Large parts of southern and eastern Australia are currently sinking in the floods. Flood warnings are currently in effect in five of the eight states and territories. Australia’s longest river, the Murray River, is recording new highs in Victoria and flooding towns, villages and farmland far beyond its banks, which could further push up food prices.

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 residents of the town of Lismore on the east coast were once again called upon to leave the town last weekend. Many of them were in the middle of rebuilding their houses, because the city of 44,000 was only in the middle of February and March flood sunken. Much to their relief, the water level stayed below feared levels this week – at least this time.

Three years in a row La Niña last existed 21 years ago

A trigger for the heavy rain showers that have been pelting the red continent since the beginning of the year is La Niña, the girl, a weather phenomenon that has always set the pace in and around the Pacific. During La Niña periods, unusually strong trade winds blow across the tropical Pacific, driving the warm sea surface waters from the west coast of South America across the ocean to the east coast of Southeast Asia and Australia. As more cold water flows in from below, the eastern part of the Pacific is cooler than usual, resulting in lowering air currents and dry weather. In the west, however, the water stays warm, the air rises and brings more precipitation over the mainland.

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La Niña’s twin, El Niño, has the opposite effect: surface winds over the tropical Pacific are weaker than usual. The rain falls on Peru during Australia simmers in the sun under a cloudless sky and the waters heat up. Mass coral bleaching often – though not always – occurs here during an El Niño year.

The opposing weather phases oscillate back and forth about every three to seven years on average. This phenomenon is called the El Niño Southern Oscillation, or ENSO for short. Typically, La Niña lasts only a year or two, but this year is the third such event in a row. Such a “triple-dip La Niña” was last recorded in the years 1973-1976 and 1998-2001. The longer a La Niña event lasts, the greater the impact as the river beds are already filled. Then even small rain showers can cause flooding.

The Australian science organization CSIRO expects extreme La Niña events to increase this century, boosted by climate change. Average temperatures in Australia increased by about 1.47 degrees Celsius over the period 1910-2020. “The frequency of extreme La Niña events is projected to increase from one event every 23 years in 1900-1999 to one event every 13 years in 2000-2099,” said Wenju Cai of CSIRO. “Extreme El Niño events favor the development of extreme La Niña events, so we can expect more frequent swings between the opposite extremes from one year to the next.”

All the rain makes everything green – but that harbors danger

Temperature measurements of the water surface in different parts of the Pacific provide insights into the near future: The International Research Institute for Climate and Society assumes that there is a 75 percent probability that La Niña will remain present well into the Australian summer (December to February). .

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“With rivers and dams already full and catchment areas wet, any rainfall in eastern Australia can cause widespread flooding,” the Australian Meteorological Service warned. In addition, there is an unusual number of cyclones in the north of the continent, the first of which could shake up the country as early as November.

At the edge of the flood areas, forests and meadows are lush green today, as the wet spring is driving growth everywhere. A sight that has further alarm bells ringing for many Australians. Because what too much vegetation can do has been known here at least since the horror of the “Black Summer” of 2019-2020 – when huge parts of Australia were swallowed up by flames.

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