What factors led to the 2022 flood event?

Photo of Lismore’s CBD by Elise Derwin

The Richmond River catchment drains an area over 7000 square kilometres from the Border, Richmond & Nightcap Ranges. Floods are a naturally recurring event  with the earliest European records dating back to 1857. Bundjalung oral history recounts flood events over previous millennia. As Bundjalung man Oliver Costello notes, floods are a “critical ecosystem function which act to recharge and clean out catchments.” The problem is, against advice of local First Nations people, early colonial settlers decided to build permanent housing and infrastructure on the floodplain. Add large-scale deforestation into the mix and we start to understand why the 2022 flood events were so devastating.

One of the most important geographical features in the catchment is the Tweed Caldera – a remnant shield volcano that erupted 20 million years ago. Rain that falls on the edge of the caldera, within the catchments of the upper Richmond River (through Dairy Flat & Kyogle) and the Wilsons River (passing Eltham & Lismore – and including Terania, Leycester & Goolmangar Creeks) flows downriver to Ballina. It’s pretty fascinating that water from Upper Wilsons Creek travels all the way to the mouth of the Richmond – a distance of almost 200km, absorbing water from every creek and tributary along the way.

From 23 Feb to 9 March 2022, an extraordinary rainfall event took place over Eastern Australia. This was the consequence of a series of complex weather patterns that all persisted for several days. Firstly, an “atmospheric river” transported large amounts of moisture in the sky towards Australia and collided with a trough off the east coast which triggered heavy precipitation over the catchment. The trough then failed to move eastwards due to a blocking high pressure system off New Zealand so it kept on raining. If we add the factors of a La Niña weather pattern, a water-logged landscape from a wet summer, warm sea surface temperatures, and king tides in the river estuary at Ballina, many towns found themselves in a perfect storm.

Weather patterns leading to the February/March floods.
Courtesy of ARC Centre for Climate Extremes

Reports from the NSW flood inquiry estimate that, at times, the speed of the water travelling through Lismore was about 26kmp/h. If we consider the volume of water involved, it’s easy to understand why houses and community halls were pulled off their foundations and carried kilometres downriver. The first colonial industry in the Richmond catchment was harvesting Australian Red Cedar, then came the clearing of vast areas of forest for pastoral activities. Bare paddocks lose their ability to absorb water much faster than forests. Trees, shrubs and groundcovers also act as obstacles to slow the flow of water across the landscape.

Now for the elephant in the room: climate change. Human-induced climate change is “fundamentally affecting our climate” notes Professor Andy Pitman from the ARC Centre for Climate Extremes. But he concedes that “estimating the effect of climate change on [the flood event] is probably beyond current capabilities.”  Scientific research emphasises the increasing unpredictability and volatility of our climate. But to say that it was the only factor that led to the floods of 2022 would be overly simplistic. A colonial legacy of harmful natural resource management has reduced the resilience of Country to cope with extreme events. We need to look at policies like reforestation and more considered urban planning on floodplains if we are to mitigate the effects of future floods.

Various case studies from the Independent NSW flood inquiry were referenced in the process of writing this article.

There’s also an amazing visual story focussing on Lismore that was produced by the Sydney Morning Herald.

Richmond River catchment map