Precipitation in Antarctica could increase | Polarjournal
Rain falls at the French Dumont d’Urville station in the eastern Antarctic coast on New Year’s Day 2014. (Photo: Bruno Jourdain UGA / CNRS / IPEV)

Rainfall could increase in amount, frequency and intensity over the next 80 years along the coast of Antarctica, a new studypredicts. By 2100, if greenhouse gases continue to be released at a high level, rain might increase by 240% on average across the continent. The increase in precipitation could promote the melting of some large ice sheets on the southern continent. This would consequently contribute to a rise in sea levels around the globe.

Cape Adare is home to the world’s largest breeding colony of Adelie penguins with over 250,000 breeding pairs. Chicks are particularly vulnerable to rain as their plumage is not yet waterproof. The cold water directly on the skin leads to hypothermia and death by freezing. (Image: Heiner Kubny)

Rain can also have dramatic consequences for emperor and Adélie penguin chicks. Since chicks’ feathers aren’t yet waterproof, they can freeze when the wet weather subsequently cools and winds pick up. The breeding season of one of the biggest colonies of Adélie penguin colonies around the Dumont d’Urville research station in southeast Antarctica saw complete failure in the 2013-2014 season due to rainfall.

“We expect not only more frequent rain events but also more intense rain events,” said Etienne Vignon from the French National Center for Scientific Research and Sorbonne University in Paris. Vignon is first author of the new study, published in Geophysical Research Letters, and is currently working in the laboratory of study leader Professor Alexis Berne at the EPF Lausanne in Switzerland.

Most of the precipitation in Antarctica is snow. Rain is uncommon and when it does occur, it is usually found on the coasts of the continent. The new study estimates that rain falls an average of up to four days per year over the coast of eastern Antarctica and an average of more than 50 days over the northwestern Antarctic Peninsula.

Where the rain falls: yearly rainy days across Antarctica, on average, from 1979-2017, as reported by ten research stations. The darker blue and green areas experienced more rainy days. (Graphic: Vignon et al. (2021) Geophysical Research Letters / AGU

But this may be changing. Vignon and his coauthors set out to measure and predict future rain on the continent after researchers noted an uptick in rain events.

The researchers wanted to learn how common rain was in Antarctica, and how it might be affected by climate change. However, traditional climate tracking systems aren’t good at predicting rainfall due to the extreme weather. “It’s still a challenge to measure precipitation in Antarctica,” Vignon said.

Dr Alexis Berne (left) is Associate Professor at the Laboratory of Environmental Remote Sensing at the EPF Lausanne and study leader. One of his areas of expertise is precipitation research in polar regions. Dr Etienne Vignon (right), the lead author of the study, originally hails from the Sorbonne and is an atmospheric physicist currently working in the laboratory of Alexis Berne in Lausanne. Image: Screenshot Youtube video EPFL News

Vignon and his co-authors gathered information about rain from several decades of observation reports from 10 research stations spread around the continent. Vignon and his co-authors gathered information about rain from several decades of observation reports from 10 research stations spread around the continent. They matched these reports, based on ground observations, with what they call atmospheric re-analysis—a combination of model simulations and various kinds of observations from sensors like radiosounding, radar and radiometers at ground level or onboard satellites—to attempt to find a type of signature that indicates rain in the harsh continent.

They came up with a climatology of rainfall occurrence over the past 50 years covering all of Antarctica, beyond the areas immediately surrounding the 10 research stations.

Most of the rain happened along the coasts and the Antarctic Peninsula, the area where penguin colonies come ashore for breeding. “On average rain almost never occurs on the high plateau because the temperature is too cold,” Vignon said.

Overall, rainfall increased over the peninsula between 1955 and 1999. Surprisingly, the increasing trend reversed from 2000 to 2015, actually decreasing for a period. Vignon said this likely has to do with large natural variability of the climate in this region.

The emperor penguin chick is completely unprotected. If moisture is added to this, the chance of survival is zero. (Image: Heiner Kubny)

Forecast calls for rain

But the researchers also wanted to see what would happen in the future. They combined this climatology of past rainfall with seven available future climate scenarios outlined in the CMIP6 by theWorld Climate Research Programme, an international program that helps to coordinate global climate research. The results showed how rainfall might change in the different scenarios through 2100. No matter which scenario they ran, the models showed the same trend.

Increasing rain could have dire consequences for the penguins that nest along the coasts. But it could also impact sea level rise, as rain might enhance the melting and breakup of ice shelves, particularly the Ronne and Ross ice shelves in western Antarctica. “Rainfall can enhance the melting of the snowpack,” Vignon said.

Heiner Kubny, PolarJournal

Link to the study: Vignon, É., Roussel, M.‐L., Gorodetskaya, I. V., Genthon, C., & Berne, A. (2021). Present and Future of Rainfall in Antarctica. Geophysical Research Letters, 48, e2020GL092281.

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