Bigger, badder storms coming in the years ahead, and California is right in the path

[Auggie]

San Francisco Chronicle / July 15, 2020

California’s wild weather swings, from pounding rain to drought and from fires to floods, are widely expected to worsen as the climate warms. A study released Wednesday shows just how severe things might get, and it’s not pretty.

The biggest of Pacific storms will dump as much as 40% more water on the Sierra, boost the hourly rate of rainfall in the state’s hills and valleys by an average of 32% and be about 4 degrees Fahrenheit warmer upon landfall.

The findings, which are focused on a weather phenomena known as atmospheric rivers, mean that a worst-case storm scenario, on par with the Great Flood of 1862 that turned the Central Valley into a raging sea and took countless lives, is an increasingly real possibility.

(probably paywall): https://www.sfchronicle.com/environment/article/Bigger-badder-storms-coming-in-the-years-ahead-15411249.php

Article highlights:

• Atmospheric rivers are becoming more water-logged as temperatures climb. With every 1.8 degree of temperature rise, the atmosphere can hold 7% more water vapor.

• Category 5 atmospheric rivers will each drop an average of 3.9 to 5.9 more inches of rain and snow on the western slopes of the Southern and Central Sierra in coming decades, according to the study.

• On average, the storms will bring 18% more precipitation to the range, though some spots will see as much as 40% more.

• Storms will be accompanied by an increase in high-altitude wind speeds

“A 20 to 30% increase in precipitation might not sound like a big increase in a lot of ways, but it is for every flood wall, every levee, every dam. Even very high thresholds (for this infrastructure) are not infinite and eventually you will exceed them.” -- Daniel Swain, climate scientist, and one of three UCLA researchers who authored the paper.

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Here's a link to the report on Science Advances: https://advances.sciencemag.org/content/6/29/eaba1323. The intro is posted below:

Precipitation extremes will likely intensify under climate change. However, much uncertainty surrounds intensification of high-magnitude events that are often inadequately resolved by global climate models.

In this analysis, we develop a framework involving targeted dynamical downscaling of historical and future extreme precipitation events produced by a large ensemble of a global climate model. This framework is applied to extreme “atmospheric river” storms in California.

We find a substantial (10 to 40%) increase in total accumulated precipitation, with the largest relative increases in valleys and mountain lee-side areas.

We also report even higher and more spatially uniform increases in hourly maximum precipitation intensity, which exceed Clausius-Clapeyron expectations.

Up to 85% of this increase arises from thermodynamically driven increases in water vapor, with a smaller contribution by increased zonal wind strength.

These findings imply substantial challenges for water and flood management in California, given future increases in intense atmospheric river-induced precipitation extremes.

[Auggie]

1. BTW, a lot of America's food supply is grown in the Central Valley

[msongs]

2. higher snow level means more runoff during storms instead of late spring melting nt

[dhill926]

3. author T.C. Boyle saw this coming in his novel...

A Friend of the Earth....

[Auggie]

4. Levee repair and upgrade is already desperately needed

The potential for it is to get really ugly. We lose property. We lose farm land.

[Brother Buzz]

5. You can write bigger, badder droughts into the equation, too

The biblical flood of 1861-1862 was followed a horrific drought of 1862-65. Economically the drought was a catastrophe for the state of California, and spelled the end of the Californios cattle empire, many losing their land grants in the southern part of the state which was hardest hit by the drought.

Ironically, the floods enriched the land and paved the way to obscene bumper crops of grain in the north; grain producers pushed the cattle industry aside became the new power brokers in California.

[Auggie]

6. +1