Warming will make downpours in California even wetter, study finds

As damaging as more than 32 trillion gallons of rain and snow have fallen on California since Christmas, the worst-case global warming scenario could drive future similar downpours by a third by the middle of this century, according to a new study. .

The strongest of California’s atmospheric river storms, long, wide columns of moisture that form over an ocean and flow across the sky over land, would likely get an overall 34% total increase. precipitation, or another 11 trillion gallons more that just fell. This is because rain and snow are likely to be 22% more concentrated at their peak in places that get very soggy, and to fall over a considerably larger area if fossil fuel emissions grow out of control, according to a new study published in Thursday’s journal Nature Climate Change.

The entire western United States is likely to experience a 31% increase in precipitation from these worst of the worst storms in a warming world due to more widespread and heavier rainfall, according to the study.

Scientists say the worst-case scenario, which is about 4.4 degrees Celsius (7.9 degrees Fahrenheit) of warming since pre-industrial times, seems a little more unlikely as efforts to control emissions are underway. If countries follow through on their promises, temperatures are on track to rise by about 2.7 degrees Celsius (4.9 degrees Fahrenheit), according to Climate Action Tracker.

The National Weather Service estimated that California averaged 11.47 inches of precipitation across the state from December 26 to January 17, including 18.33 inches in Oakland and 47.74 inches at one location 235 miles north of San Francisco, due to a devastating series of nine atmospheric rivers which caused power outages, flooding, levee breaches, mudslides and landslides. At least 20 people died.

“It could be even worse,” said study author Ruby Leung, a climate scientist at the US Pacific Northwest National Laboratory. “We need to start planning how we might deal with this.”

Leung used regional-scale computer simulations to predict what the worst of the western winter storms will look like between 2040 and 2070 in a scenario where carbon emissions have gone haywire. He looked at the total precipitation, how concentrated the peak of rain and snow would be, and the area affected. All three factors grow for the West in general. California is forecast to get the largest increase in maximum precipitation, while the Southwest is likely to see more rain due to a large jump in rainfall area. The Pacific Northwest would see the least amount of juice of the three areas.

Overall precipitation is reduced somewhat by adding all the factors together, because as peak rainfall grows, rainfall at the edges of storms is expected to weaken, according to the study.

There are two types of storms that Leung said he is concerned about: flash floods of heavy rain concentrated in a small area, and larger, slower floods that occur due to accumulation of rain and snow over a large area. Both are bad, but flash floods do more damage and hurt people more, he said.

and those Flash floods they are likely to be made worse by what Leung’s paper calls a “sharpening” effect that occurs in an increasingly warming world. That means more rain concentrated in the central areas of the storms, falling at higher rates per hour, while rain on the outer edges is slightly weaker.

This happens due to the physics of rain storms, Leung said.

Not only can the atmosphere hold 4% more moisture per degree Fahrenheit (7% per degree Celsius), but that is what happens in the storm that changes and makes the precipitation drop even lower, Leung said. You have air rising within the storm with more water vapor condensing to produce rain and snow; it then releases heat “which makes the storm more vigorous and stronger,” he said.

When water steam It condenses, falling as rain and snow along the edges of the storm, but the warming squeezes the precipitation toward the center, Leung said.

“The concepts and impacts of how precipitation characteristics are likely to change are well quantified and well explained,” said David Gochis, an expert on how water affects climate at the National Center for Atmospheric Research in Boulder, Colorado. , which was not part of the study.

Using computer simulations, Leung chose the most severe worst-case scenario for how the world’s carbon emissions will grow. It’s a scenario that used to be called business as usual, but the world isn’t on that track anymore. After years of negotiations on climate and the growth of renewable fuels, the world is headed for less than worst-case warming, according to climate scientist Zeke Haus father of the technology company Stripe and Berkeley Earth.

“We are providing more than one worst of casesbut understanding that if we take steps to reduce emissions in the future, we could end up better off,” Leung said. “If we control emissions and reduce global warming in the future, we can limit the impacts of climate change on society, particularly flooding. and the extreme precipitation that we are talking about in this study”.

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