It is difficult to assess the direct impact of climate change on floods. It is the sum of many phenomena, and according to the experts, the preparedness is not at the best level either.
Flooding caused by heavy rains has plagued southeastern Australia in recent days. Some parts of New South Wales have had a month’s worth of rain in a couple of days.
In a part of southern Sydney, it rained up to 240 millimeters in a day, or 17 percent of the amount that rains in the city on average in a year, the Australian broadcasting company ABC said on Tuesday.
By Tuesday, almost 50,000 people in the state have already been advised to evacuate. In addition, 28,000 others have been told to prepare for evacuation, reports the AFP news agency.
On Tuesday, the rain was expected to ease in Sydney and move north. However, the flood situation will not ease in an instant, and the danger is not over in Sydney either, officials estimate.
The last flood was in March-April, when they caused more than three billion dollars, or just under three billion euros, in damages in New South Wales and southeast Queensland.
The flood is already the fourth in two years, which is why the reasons for the repeated phenomenon are being considered.
It is difficult to show the direct effect of climate change on individual floods, says an Australian disaster analyst Tom Mortlock news agency Reuters.
However, according to him, most climate models predict that rains will become more common in Australia. Rising temperatures also lead to an increase in humidity.
Also a climate scientist Andrew King from the University of Melbourne says In The Guardian (you will switch to another service)that the climate crisis has been proven to increase rainfall, but it is difficult to show what role it plays in the severe flooding in Australia in recent days.
La Niña plays a big role
The opposite of El Niño, the La Niña phenomenon, which affected Australia two years in a row, has been cited as a major factor in the floods. It recurs irregularly and usually lasts from half a year to a year.
During La Niña, strong trade winds in the Pacific Ocean push warm surface water towards Asia and increase rainfall in Australia.
La Niña ended at the end of June, but according to the Australian Bureau of Meteorology, it may form again this year.
Another phenomenon is the Indian Ocean dipole, which has three different phases: neutral, positive and negative. The dipole turned negative at the end of May, when westerly winds blowing lower along the equator intensify, and warm water accumulates north of Australia.
The water is warmer than normal in the east and colder than usual in the west. So moist air flows towards Australia.
The soil does not absorb more than its amount
Traces of La Niña can also be seen in the ability of the Australian soil to receive heavy rain.
The Hawkesbury River valley, north of Sydney, is a floodplain that is also fed by five tributaries. During the last couple of years, the rains brought by La Niña have filled the dams and saturated the soil, creating favorable conditions for floods.
– In practice, the catchment area of the east coast has almost no capacity to absorb water, says Tom Mortlock.
This has sparked debate about how well Sydney is prepared for flooding. Professor Stuart Khan of the University of New South Wales believes that the Warragamban Dam in Sydney is considered too full. About 80 percent of Sydney’s water is stored in the dam.
The dam was 97 percent full and overflowing. According to Khan, it would be better to keep the occupancy rate at 60 percent to reduce the effects of flooding.
Sydney’s population has grown rapidly in recent decades and that has increased the amount of construction on the floodplain. We have not been able to prepare for floods, because before the recent events there had been no major floods in the area for decades.
For the same reason, the bridges in the area are also too low, there are few evacuation routes and they are incomplete, says an environmental researcher from Western Sidney University Ian Wright.