As I write this editorial, rivers around Sydney are flooding for the second time this year and the fourth time in three years. There continues to be surprise expressed in the media about the frequency of the flooding and many point the finger at climate change. However, an objective assessment of the floods shows that these are generally events with between a 10% and 5% AEP, and in the long term, are occurring with the regularity expected. Between 1990 and 2020 there were no floods on any of these rivers.
When I started in floodplain management in the early 1990s, Professor Robyn Warner had postulated that there have been “drought dominated” and “flood dominated” periods along the East Coast with each lasting three or four decades. It would appear that Sydney, at least, has emerged from a drought dominated period and is at the start of a flood dominated period.
We report this month that the Bureau of Meteorology is forecasting a 50/50 chance of another La Niña this spring which would be the third in a row, further suggesting we are in the first few years of a flood dominated period.
We also report on the indirect impacts still being felt from the February/March floods throughout Queensland and NSW. As our societies become more affluent and more interconnected, these impacts become larger and more widespread. Thirty years ago, the loss of power and telecommunications would not have resulted in loss of internet access and its cascading impacts nor cessation of most financial transactions. Minor flooding of a car would not have resulted in its complete write off. Yet these are the new impacts of flooding which we need to account for when making floodplain management decisions.
Australian climate modellers are suggesting that further melting of the icecaps could change salinity levels in the Atlantic Ocean which will turn off the Atlantic overturning circulation. This in turn will result in a build-up of heat south of the Equator and push warm water in the tropical Pacific westwards. This would produce permanent La Niña conditions.
So, while climate change might not be to blame for the flooding we have been experiencing this year, it may push us into a permanent flood dominated regime. Are we building infrastructure, systems and communities which will be resilient to that?