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Scientists warn of the risk of major catastrophic flooding in California

2022-08-14T16:46:13.797Z


Climate change is increasing the likelihood of torrential storm surges in America's most populous state, adding to the threat of a massive earthquake.


The San Andreas fault, between the North American plate and the Pacific plate, keeps California under threat of a devastating earthquake, colloquially called the

big one

.

That risk has given to rivers of ink, scientific reports, documentaries, novels and movies.

However, scientists have now added another catastrophic omen for the inhabitants of the most populous state in the United States: mega-floods, with sequences of storms that could discharge up to 3,200 liters per square meter in some areas over 30 days.

The problem Californians routinely deal with is drought.

This year's is being especially harsh and has forced the imposition of drastic restrictions on consumption.

Climate change, however, is increasing the risk of extreme weather events, as torrential rains in Death Valley, the driest place in the United States, have shown this month.

The rain that has fallen there is nothing next to what may be left in future storm surges from the Pacific, scientists warn.

More information

Is the San Andreas fault warning us of the 'Big one'?

An article published by

Science Advances

notes that "climate change has already doubled the probability of an event capable of producing catastrophic flooding, but larger increases are likely in the future due to continued warming."

Climate researchers Xingying Huang and Daniel L. Swain have studied the physical characteristics of worst-case scenario extreme storm sequences capable of leading to mega-flood conditions, using a combination of climate model data and high-resolution weather modelling.

In fact, California has already experienced massive flooding.

There have been episodes of prolonged to intense rains in the last century, but the historical reference that scientists have taken is that of the great flood of late 1861 and early 1862. It was a series of weeks-long winter storms, produced a widespread catastrophic flooding of virtually all of California's lowlands, "transforming the interior of the Sacramento and San Joaquin valleys into a temporary but vast inland sea nearly 300 miles in length, and inundating much of the coastal plain, now densely populated, in the present counties of Los Angeles and Orange”, they remember.

Recent estimates suggest that floods equal to or greater than those of 1862 occur five to seven times per millennium, which is equivalent to an annual probability of 0.5% to 1% or once every 100 or 200 years.

It is estimated that some 2,500 liters per square meter fell at some points, the equivalent of two and a half meters of water, in 40 days.

atmospheric rivers

The West Coast of the United States is a regular passageway for atmospheric rivers from the Pacific, specifically from the area north of the Hawaiian Islands, and more intense in El Niño years.

They are bands of concentrated humidity in the atmosphere that transport water vapor and water in the form of clouds.

Thousands of kilometers long and a few hundred kilometers wide, atmospheric rivers can carry a greater flow of water than any of the great rivers on Earth.

Arriving in California, these rivers of moisture in the form of clouds collide with the mountains, rise and when the water vapor cools, it condenses causing rain (or snow, in the highest areas).

According to the study, this pattern will be repeated, but with new features.

“Future extreme storm sequences will bring with them more intense moisture transport and increased global precipitation, along with higher freezing levels and decreased snow/rain ratios that, together, produce flow much higher than that of historical events”, point out the researchers.

They also warn of a risk of more intense precipitation in individual storms.

Floods this August in Death Valley, California.JOHN SIRLIN (REUTERS)

The two scenarios that scientists have considered speak of accumulated rainfall in 30 days of 500 liters per square meter in large areas of California, with fairly extensive areas that would receive more than 1,000 liters and a maximum of 2,150 liters, in the first scenario.

In the second, the figures are higher: 700, 1,400 and 3,200 liters, respectively.

Scientists warn that this risk is being underestimated and, above all, that it is increasing due to global warming.

Our initial atmospheric modeling results presented here demonstrate that extremely severe winter storm sequences, previously considered exceptionally rare events, are likely to become much more common under essentially all possible future climate tracks. .

Taken together, the results of previous work and of this study illustrate the growing urgency to plan for and mitigate potentially catastrophic flood risks in California in a warming climate.

There is another small consolation.

Unlike earthquakes, which science has not yet been able to anticipate in advance, the sequence of atmospheric rivers will be seen coming.

There will be the possibility of warning of the risk of strong storms about five days in advance to try to prepare and mitigate the damage.

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Source: elparis

All news articles on 2022-08-14

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