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New work led by Xingying Huang on extreme #AtmosphericRiver storms in California in a warming climate is out today in @ScienceAdvances (open access)! A thread discussing our findings and their implications follows. #CAwx #CAwater #CAclimate (1/n) https://advances.sciencemag.org/content/6/29/eaba1323
Top-level findings: we find that the most intense atmospheric river storms in California will be become considerably more intense as the climate warms, bringing substantially more precipitation overall as well as higher precipitation intensities. (2/n)
https://advances.sciencemag.org/content/6/29/eaba1323
https://advances.sciencemag.org/content/6/29/eaba1323
We find that largest *absolute* increases in extreme AR precip occur where you might expect: along windward slopes of Sierra Nevada & Coastal Mountains. But...the largest *relative* increases occur in historically rain-shadowed areas--Central Valley & Sierra lee side. (3/n)
Precipitation intensity during the strongest portion of extreme AR storms increases by an even larger margin than event total accumulation--resulting in a very large (~50%) increase in hourly rainfall rates in some places! (4/n)
Vast majority of precip increase (85%) is attributed to direct thermodynamic effects of warming--i.e., exponential increase of atmospheric H20 vapor holding capacity w/increasing temperature. Remainder comes from slight increases in transport winds. (5/n) https://advances.sciencemag.org/content/6/29/eaba1323
Interestingly, we also find a general decrease in orographic precipitation *efficiency* during extreme AR events (i.e., the increase precipitation is somewhat less that we would expect given the even larger increases in vapor transport). (6/n) https://advances.sciencemag.org/content/6/29/eaba1323
Still, the possibility of very extreme and historically unprecedented integrated vapor transport events in a warming climate really stands out. (Keep in mind that these value are *5-day averages!*) (7/n)
Perhaps unsurprisingly, extreme ARs in the future will also be much warmer than their historical counterparts--on the order of 3-6F warmer. That's more than enough to fundamentally alter the rain-snow balance in the Sierra Nevada. #CAwx #CAwater (8/n) https://advances.sciencemag.org/content/6/29/eaba1323
Methodological note: we used a modeling approach that leveraged both high-resolution weather model (4km WRF) & climate model large ensemble (CESM-LENS)--enabling us to simulate physically realistic fine-scale ARs, but also obtain large sample size.(9/n) https://advances.sciencemag.org/content/6/29/eaba1323
What does all of this mean? Well, as has been case historically, California's biggest storms & flood events are still going to be associated w/ #AtmosphericRiver events. But they are going to become much wetter, and warmer, as climate warms. (10/n) https://advances.sciencemag.org/content/6/29/eaba1323
AR flood risk will likely rise quite substantially. 3 factors act in concert to increase runoff: 1) greater total precip volume, 2) higher precip intensity, & 3) more rain (vs. snow) in mountains, causing larger fraction of water to enter watersheds immediately. (11/n) #CAwater
For a more in-depth discussion, check out my new Weather West blog post linked below. I also want to thank Xingying Huang and @ProfAlexHall for their hard work in seeing this project to fruition over the past several years! (12/12) https://twitter.com/Weather_West/status/1283464940284571648?s=20
