How La Niña impacts WA coastline

The Bureau of Meteorology recently declared that Australia is officially experiencing its third La Niña this summer. This relatively rare climate event is typically marked by increased rainfall and flooding risks, as well as cooler daytime temperatures.

Although the Eastern States of Australia have been hit the hardest, Western Australia is still experiencing the effects of La Niña weather conditions. According to experts, rising sea levels are compounding the movement of WA beaches, resulting in greater growth and erosion.

Here’s more on this phenomenon, and how it impacts our coastline.

What is La Niña?

La Niña is a climate pattern in the Pacific Ocean that affects the weather worldwide. It’s an unusual weather pattern, as it breaks from typical conditions, and results in changes to weather all around the world.

Typically, trade winds in the Pacific Ocean blow west alongside the equator, moving warm water towards Asia from South America. This warm water is replaced by cold water, which rises up from the depths beneath (this is called upwelling).

La Niña breaks this typical pattern by pushing even more warm water towards Asia with stronger than average trade winds. The La Niña is part of a phenomena known by scientists as the El La Niño-Southern Oscillation (ENSO) cycle.

El Niño is a part of this cycle, which can last from nine to 12 months, and in some cases, years. There’s no regular schedule for El Niño and La Niña, however El Niño is known to occur more regularly, while La Niña conditions typically take place every two to seven years.

How does La Niña impact WA coastlines?

According to oceanographers, WA’s coastline is experiencing greater growth and erosion as a result of La Niña conditions. This growth and erosion is the result of higher sea levels and a stronger Leeuwin Current.

Dr Jeff Hansen, who is an Associate professor at the University of Western Australia’s Oceans Institute, told ABC News that the Leeuwin Current is stronger during La Niña, which results in more water being pushed against WA coastlines.

“The Leeuwin Current is weakest in the summer and strongest in the winter,” he said.

“With that seasonal strength variation, we have about 20 centimetres of higher sea level in the winter than what we do in the summer, and then when we have a La Niña case you add another 10 to 15 centimetres on top of that.”

Dr Ming Feng, senior principal research scientist for oceans and atmosphere at CSIRO told ABC News that the La Niña was likely to cause an increase in storm events, which in turn would result in greater coastal erosion.

“If we have a one centimetre sea level rise, roughly one metre of the coastline will be affected,” he said.

“I think when you have a sea level rise, whether it be a steady rise or during an extreme event, the coastline will be more impacted.”

Coastlines are dynamic

Over the past two years, the WA Government has spent $13 million, in a bid to stabilise the state’s coastline. Erosion in particular has impacted beaches across WA, including Bunbury and Geraldton, who were hit hard over the past 12 months.

Dr Robbi Bishop-Taylor, who is a coastal earth observation scientist for Geoscience Australia, told ABC News that he draws on satellite data collected over the past 30 years to discover how coastlines change over time.

Dr Bishop-Taylor said that when zooming in on Australia’s coastlines, there is significant variability.

“So you get beaches that are eroding really rapidly, but then what you do find is that you start to zoom out and just up the shore of an eroding beach, you’ll often find a beach is growing just at the same rate as the sand slowly moves along the coastline,” he said.

Monitoring your coastline

More and more local governments in WA are investing in coastal mapping, to gain a better understanding of how coastal areas respond to weather conditions over time. This data is then used to effectively plan and manage coastal areas for future generations.

Land Insights recently performed a coastal mapping project for the Shire of Gingin, which can be read here.

If you think coastal mapping would be valuable to your coastal management planning, please get in touch to find out how we can assist you.

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