Satellite Images Reveal How Beaches Around The Pacific Vanish During La Niña
Surfers, particularly those living on Australia’s East Coast, are well aware of the surf conditions wrought by La Niña. Three consecutive summers have shown just what the climate driver known as ‘the little girl’ is capable of.
The causal chain goes something like this: During La Niña stronger than normal tradewinds blow across the Pacific towards Australia, warm water piles up on our eastern shore, this creates an increase in tropical activity including easterly winds, which in turn leads to a surfeit of easterly swell across the whole Eastern Seaboard.
However, the causal chain doesn’t end there. It may not be quite as exciting to surfers, but all that La Niña swell energy then leaves its mark on the coast. To wit, the shoreline erodes. Without time to recover, the coast’s natural buffer - i.e beach sand - is transported from the beaches to the ocean.
When it happens, the media usually focuses on erosion hotspots such as Wamberal and Collaroy, however a recent study by four Sydney scientists has shown that almost all beaches become thinner during La Niña. Meanwhile, on the other side of the Pacific, beaches in California and South America expand as sand piles up under ideal conditions.
Flick the switch to El Nino and the opposite becomes true: Beaches in Australia recover and expand in width, while those on the Pacific’s eastern rim begin to erode under sustained storm activity. It’s no coincidence that the very best Hawaiian seasons have been shown to coincide with El Nino.
At the heart of the research, which was led by Kilian Vos, was access to millions of satellite images taken over the last forty years. The scientists created a timeline of aerial imagery, and then set it against the ENSO (El Nino Southern Oscillation) cycle over the past four decades to confirm their suspicions.
To date, scientists have relied on either anecdotal evidence or a hodgepodge of sources to understand coastal cycles. Access to satellite imagery provides them with a consistent, long term source of information, which is necessary for scientific confirmation.
The scientists concerned have both released a paper on their findings, and also created a website, CoastSat, which tracks coastal changes across thousands of beaches in the Pacific Rim.
According to Dr Mitchell Harley, one of the four scientists who worked on the project, the findings are “a very powerful tool for coastal councils and State Governments.”
With the current level of knowledge, La Niña can be predicted with a high degree of confidence from six to twelve months out. Rather than being reactive, “they [councils and governments] can now see how the coastline will respond,” says Dr Harley, “and be proactive by taking early measures to protect the coast.”
“This might mean boosting their staff levels,” adds Dr Harley, “shifting their resources, or protecting equipment assets.”
There’s also a project planning perspective, whereby existing or planned projects will have to be considered in the context of a soon-to-be altered coastline.
Even sand nourishment, which has been the classic last ditch effort by councils having their coastline battered, can be organised in advance. Perhaps dumped early as a preventative measure, rather than later as a cure.
Though such planning springboards off the back of Dr Harley’s work, there are other more compelling - read: scientific - aspects of the research. “In the scientific community,” says Dr Harley, “there’s conjecture that the cyclical nature of ENSO may be changing.”
And this is the big thing. Now that the scientists have a solid database to work off, all future ENSO cycles can be compared against the past.
“It gives us the power to understand what’s happening with the ENSO cycles, “ says Dr Harley.