EXPLAINER: Factors behind Sydney’s recent flood emergencies

Jul 5, 2022, 11:01 AM | Updated: Jul 8, 2022, 6:42 am
A man paddles his kayak through a flooded street at Windsor on the outskirts of Sydney, Australia, ...

A man paddles his kayak through a flooded street at Windsor on the outskirts of Sydney, Australia, Tuesday, July 5, 2022. Hundreds of homes have been inundated in and around Australia's largest city in a flood emergency that was impacting 50,000 people, officials said Tuesday. (AP Photo/Mark Baker)

(AP Photo/Mark Baker)

CANBERRA, Australia (AP) — Parts of Australia’s largest city have been inundated by four major floods since March last year, leaving weary residents questioning how many times they can rebuild.

The latest disaster follows Sydney’s wettest-ever start to a year with dams overflowing and a sodden landscape incapable of absorbing more rain that must instead run into swollen waterways.

Here are the climate, geographic and demographic factors behind Sydney’s latest flooding emergency.

___

LEADERS BLAME CLIMATE CHANGE

New South Wales state Premier Dominic Perrottet said government and communities need to adapt to major flooding becoming more common across Australia’s most populous state.

“To see what we’re seeing right across Sydney, there’s no doubt these events are becoming more common,” Perrottet said on Monday.

Prime Minister Anthony Albanese said the fourth major flood event across Sydney following devastating wildfires in the same region during the 2019-2020 Southern Hemisphere summer were evidence of the need for climate action.

“What we know is that Australia has always been subject of floods, of bushfires, but we know that the science told us that if we continued to not take action globally on climate change, then … extreme weather events would be more often and more intense,” Albanese said on Wednesday.

“What we’re seeing, unfortunately, is that play out,” Albanese added.

___

LA NINA OUT, OTHER WEATHER PATTERNS IN

Two La Niña weather patterns brought above-average rainfall across Australia’s east coast in 2021 and this year. The second was declared over last month, but the Bureau of Meteorology forecast a wetter than usual Southern Hemisphere winter for Sydney and a 50-50 chance of La Niña returning this year.

The bureau says two climate drivers led to Sydney’s flooding since Saturday.

The flooding was influenced by the Indian Ocean Dipole, which refers to the difference in sea surface temperatures between the western and eastern Indian Ocean. In the negative phase, warmer waters concentrate near Australia, leading to above-average Southern Hemisphere winter-spring rainfall as more moisture is available to weather systems crossing the continent. The IOD has repeatedly dipped into its rain-bearing negative phase in the past month and is expected to stay negative within months.

A second influence was the positive Southern Annular Mode. The SAM refers to the non-seasonal, north-south movement of the strong westerly winds that blow almost continuously in the mid to high latitudes of the Southern Hemisphere. In the positive phase, the SAM directs more moisture-filled air than usual into eastern Australia, driving above-average rainfall and more east coast lows in winter.

During the latest rainfall event, extraordinarily warm waters off the Australian coast, 21 to 23 degrees Celsius (70 to 73 degrees Fahrenheit), provided extra energy and moisture to a deep trough and east coast low, concentrating heavy rainfall to one 24-hour period that started at 9 a.m. Saturday.

Several rain gauges in Sydney and its surrounding area set July or all-time records.

___

GEOGRAPHY AND DEMOGRAPHY

Much of Sydney’s rain drains into a river system prone to spilling over, but economic interests have largely blocked moves to mitigate flooding.

A 22,000-square-kilometer (8,500-square mile) rain catchment covering the Blue Mountains on Sydney’s western fringe and the city of 5 million’s western suburbs drain into the Hawkesbury-Nepean river system, which is the epicenter of some of the worst flooding.

The river system faces an extreme flood risk because gorges restrict the rivers’ seaward flow, often causing water to rapidly back up and spill across the floodplain after heavy rain, said Jamie Pittock, Australian National University professor of environment and society.

The Hawkesbury-Nepean Valley was home to 134,000 people and that population was projected to double by 2050 as Sydney’s population and real estate prices grow, he said.

“The potential economic returns from property development are a key driver for the lack of effective action to reduce flood risk,” Pittock said.

The state government wants to raise the wall of the Warragamba Dam, Sydney’s main reservoir, to reduce flooding in the valley.

But some argue that raising the wall would control only half the floodwater and won’t prevent major flooding delivered by other rivers in the region, said Dale Dominey-Howes, Sydney University’s professor of hazards and disaster risk sciences.

Copyright © The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

AP

Czech policemen control a truck at the border with Slovakia in Stary Hrozenkov, Czech Republic, Thu...
Associated Press

Czechs relaunch checks at Slovak border amid migration wave

PRAGUE (AP) — Czech police fired warning shots in the air before detaining the driver of a van carrying 15 migrants Thursday morning after the Czech Republic and Austria renewed checks at the border with Slovakia amid a new wave of migration. Czech police reported traffic delays, especially for trucks, after the measure became effective […]
1 day ago
Associated Press

3 Russian cosmonauts return safely from Intl Space Station

MOSCOW (AP) — Three Russian cosmonauts returned safely on Thursday from a mission to the International Space Station. The Soyuz MS-21 spacecraft carrying Oleg Artemyev, Denis Matveyev and Sergey Korsakov touched down softly at 4:57 p.m. (1057 GMT) at a designated site in the steppes of Kazakstan about 150 kilometers (about 90 miles) southeast of […]
1 day ago
Associated Press

Pakistani court acquits ex-PM’s daughter in corruption case

ISLAMABAD (AP) — A court in Pakistan’s capital city on Thursday acquitted the daughter of former Prime Minister Nawaz Sharif after she was sentenced to seven years in prison over charges connected with the purchase of luxury apartments in London. Maryam Nawaz, the vice president of the ruling Pakistan Muslim League, said outside the Islamabad […]
1 day ago
People wearing face masks to protect against the spread of the coronavirus take morning exercises a...
Associated Press

Taiwan to end quarantine for arrivals starting Oct. 13

TAIPEI, Taiwan (AP) — Taiwan on Thursday said it will end mandatory COVID-19 quarantines for people arriving from overseas beginning Oct. 13. The Central Epidemic Command Center announced that the previous weeklong requirement will be replaced with a seven-day self-monitoring period. A rapid antigen test will still be required upon arrival, but those showing no […]
1 day ago
FILE - Hong Kong pro-democracy lawmaker Ted Hui, center, argues with pro-Beijing lawmaker Junius Ho...
Associated Press

Former Hong Kong lawmaker sentenced to 3 1/2 years in jail

HONG KONG (AP) — Former Hong Kong lawmaker and pro-democracy activist Ted Hui was sentenced to 3 1/2 years in jail for criminal contempt after he skipped bail and fled overseas, missing trial for cases against him. Hui was facing charges for his role in an anti-government protest in 2019 when he left Hong Kong […]
1 day ago
Victims of heavy flooding from monsoon rains attend school at a flood relief camp in Hyderabad, Pak...
Associated Press

3 million children may miss a semester in flood-hit Pakistan

ISLAMABAD (AP) — Almost 3 million children in Pakistan may miss at least one semester because of flood damage to schools, officials said Thursday, following heavy monsoon rains likely worsened by climate change. Unprecedented deluges since mid-June have affected more than 33 million people, inundated millions of acres of land and devastated infrastructure, including education […]
1 day ago

Sponsored Articles

Anacortes Christmas Tree...

Come one, come all! Food, Drink, and Coastal Christmas – Anacortes has it all!

Come celebrate Anacortes’ 11th annual Bier on the Pier! Bier on the Pier takes place on October 7th and 8th and features local ciders, food trucks and live music - not to mention the beautiful views of the Guemes Channel and backdrop of downtown Anacortes.
Swedish Cyberknife Treatment...

The revolutionary treatment of Swedish CyberKnife provides better quality of life for majority of patients

There are a wide variety of treatments options available for men with prostate cancer. One of the most technologically advanced treatment options in the Pacific Northwest is Stereotactic Body Radiation Therapy using the CyberKnife platform at Swedish Medical Center.
Work at Zum Services...

Seattle Public Schools announces three-year contract with Zum

Seattle Public Schools just announced a three-year contract with a brand-new company to the Pacific Northwest to assist with their student transportation: Zum.
Swedish Cyberknife 900x506...

June is Men’s Health Month: Here’s Why It’s Important To Speak About Your Health

According to the Centers for Disease Control and Prevention, men in the United States, on average, die five years earlier than women.
...

Anacortes – A Must Visit Summertime Destination

While Anacortes is certainly on the way to the San Juan Islands (SJI), it is not just a destination to get to the ferry… Anacortes is a destination in and of itself!
...

Ready for your 2022 Alaskan Adventure with Celebrity Cruises?

Celebrity Cruises SPONSORED — A round-trip Alaska cruise from Seattle is an amazing treat for you and a loved one. Not only are you able to see and explore some of the most incredible and visually appealing natural sights on the planet, but you’re also able to relax and re-energize while aboard a luxury cruise […]
EXPLAINER: Factors behind Sydney’s recent flood emergencies