TAMPA, Fla. (WFLA) — A series of Atmospheric Rivers are responsible for the dramatic scenes in California this week.

Over the past week, 20 people have been killed in the state by these atmospheric phenomena.
Sciencists say they are getting stronger.

Atmospheric rivers are long, narrow conveyor belts carrying immense amounts of water – up to 25 times the daily discharge of the mighty Mississippi River. Right now, they’re aimed directly at California.

Over the past two weeks, San Francisco has been drenched by more than half a year’s worth of rain. Rivers are overflowing, sinkholes are forming, and rock slides are blocking roads.

It’s all due to a relentless parade of storms, each attached to an atmospheric river firehose, funneling storms from the humid tropics.

Yearly, Atmospheric Rivers deliver 50% of California’s water supply, but because it often comes too hard and too fast, the terrain can’t handle it. As a result, on average, 90% of California’s flood damage comes from these phenomena.

And as the air continues to warm due to climate change – these rivers hold more moisture. Research finds, so far, a 15% bump in precipitation. By the end of the century, they’re projected to be 25% larger and atmospheric river conditions could be 50% more frequent.

These images below compare moisture transport from Atmospheric Rivers. On top: what they looked like a couple of decades ago. And bottom: the expected increase in future decades.

Atmospheric River moisture transport past and future. Huang Et al. 2020

That means increasing rainfall rates too – with up to a 40% spike in precipitation projected.

Atmospheric River rainfall rates projected to increase. Huang Et al. 2020

As a result, damages in the Western US are projected to double or triple by 2100.

And because warming supercharges the water cycle, precipitation patterns are more volatile and less reliable. Dry periods are longer and drier and wet periods are shorter and more intense. A recipe for drawn-out droughts, followed by furious floods.

Exactly the kind of weather whiplash the west has seen for the past two decades.

There is some good news for the drought stricken state. Mountain snowpack is now up to 250% of normal and the US Drought Monitor shows significant improvement.

US Drought Monitor

Still, there’s a long way to go, recovering from the West’s worst drought in 1200 years.