14 November 2022

Another wet start to summer – as long as I remember, the rain’s been falling down…..

If you live on the east coast and are thinking that this spring has been unusual, perhaps not a season you’ve ever experienced before, then you are probably right. 

The Bureau of Meteorology (the Bureau) has declared that the east coast is once again in La Niña conditions, for the third year in a row. Warmer than average ocean temperatures are continuing across the western Pacific and the western Indian Ocean, creating conditions for high evaporation and onshore winds. 

The renewed La Niña will bring another spring and early summer of above average rainfall. After two La Niña periods, most catchments are saturated, and dams are full to overflowing. The ongoing heavier rainfall threatens high risks from destructive flooding for multiple communities built in river corridors, as well as risks from landslip on steep slopes and coastal erosion that impacts on our summer beach lifestyle.

Three strike La Niñas are considered pretty rare. Previous ones included 1954-57, 1973-76 and 1998-2001. They stick in your mind, as they tend to be associated with big flood and storm events, affecting large parts of the state, with vulnerable areas flooded again and again. Sound familiar? 

So, 1954-57 was the time of the Maitland Floods, which led to the development of the major civil works associated with the Hunter Flood Mitigation Scheme. The floods have featured in both documentaries and popular movies about life in Australia. 

1973-76 is associated with big storms and coastal erosion events – with apartment blocks at Collaroy undermined, the destruction of Manly harbour pool, houses falling into the sea on the central coast and the bulk carrier Sygna wrecked on Stockton Beach. 

And the floods of 2000/2001, which came in three big peaks from October through to March, have been described by Chas Keys, the former Deputy Director General of the SES, as one of the great flood periods of NSW history. During that period, virtually every river system in northern, eastern and western NSW flooded – some more than once. There were major impacts on crops, grazing land, roads, bridges, residential areas (with many people evacuated), and fish kills in estuaries. 

Before the 1950s, there are reports of extreme storm events in 1866 (the Cawarra storm which destroyed 20 ships including wrecking the paddle steamer Cawarra with the loss of 62 lives), and in 1898 when the paddle steamer Maitland was wrecked on the northern side of Broken Bay (you can still see the remains of the boiler on the rocks at Maitland Bay). Similarly, the 2007 Pasha Bulka Storm was intense, but localised in time and spatial impact. These storms were memorable and destructive, but they weren’t set within triple whammy (three consecutive years of la nina) weather events. 

The current La Niña sequence is even more unusual. Mid-term weather patterns in Australia are driven by interactions between four major influences or cycles – the ENSO (La Niña/El Niño), IOD (Indian Ocean Dipole), MJO (Madden-Julian Oscillation) and SAM (Southern Annular Mode). The BoM says that this is the first time on record (so over approximately the last 170 years) that Australia has experienced three consecutive ENSO La Niña events, at the same time as negative IOD events. A positive SAM and a strong MJO are also compounding the circumstances leading to very wet weather in eastern and northern Australia, from Tasmania and Victoria to Cape York and Arnhem Land. In contrast, the western part of the continent is more likely to be dry. 

The combined impacts of the three weather drivers are also reflected in temperature. While the coast of NSW and SE Queensland is experiencing cooler than median daytime temperatures, Tasmania and SW Western Australia are expected to experience hot conditions. 

There is a link between these unusual circumstances and climate change. The BoM says that extreme temperature and rainfall events, and the temperature of the oceans around the continent, are influenced by global warming. The records show that Australia’s temperatures warmed by around 1.47 degrees Celsius between 1910 and 2020. The result of higher average temperatures is an increased frequency of extreme events – in heat and in rainfall intensity. 

While unusual, the weather events we have been experiencing provide important lessons for effective emergency response to keep communities safe, and for promoting the connections that help to make communities more resilient. Importantly these events demonstrate the need for transformative land use and infrastructure planning, so that our cities and rural areas can successfully adapt to climate change – when these unusual events become the new normal.