Climate model suggests global warming has already doubled the risk of California megaflood

Bob Yirka is a research scientist at Phys.org.

The impact of global warming on the creation of atmospheric rivers over the Pacific Ocean and what it could mean to people living in California was described in a paper published in Science Advances.

A megaflood is not a normal flooding event, it is one that occurs over a large area and is much more severe than is normally seen, with the potential to destroy areas that are involved. Cities such as Sacramento were under ten feet of water because of the water in the valley. The bodies of over 4,000 people were left behind after the water subsided. At the time of the mega flood, only half a million people lived in California.

Megafloods are a rare occurrence in California. They happen when atmospheric conditions over the Pacific Ocean combine to form atmospheric rivers, which are long narrow regions in the atmosphere that become highly saturated with water. The water is released when the rivers go into the mountains. It has been mostly released as snow in the past, but in the future it will come down as rain.

It could last weeks, with the water filling up the valleys. In the past, mega floods only happened in California. Depending on how much the atmosphere warms up, that is likely to change as often as once every 50 years or every 30 years. It could happen any time now.

The researchers studied output from the Community Earth System Model Large ensemble and compared it to high-resolution weather modeling. The two showed that global warming has increased the likelihood of a mega flood in California. As temperatures over the Pacific rise, that risk is increasing.

More information: Xingying Huang et al, Climate change is increasing the risk of a California megaflood, Science Advances (2022). DOI: 10.1126/sciadv.abq0995 Journal information: Science Advances

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