Despite the recent prevalence of severe drought, California faces a broadly underappreciated risk of severe floods.
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"Here, we investigate the physical characteristics of “plausible worst case scenario” extreme storm sequences capable of giving rise to “megaflood” conditions using a combination of climate model data and high-resolution weather modeling", Xingying Huang and Daniel L. Swain write.
"Using the data from the Community Earth System Model Large Ensemble, we find that climate change has already doubled the likelihood of an event capable of producing catastrophic flooding, but larger future increases are likely due to continued warming.
"We further find that runoff in the future extreme storm scenario is 200 to 400% greater than historical values in the Sierra Nevada because of increased precipitation rates and decreased snow fraction.
"These findings have direct implications for flood and emergency management, as well as broader implications for hazard mitigation and climate adaptation activities.
"We design two separate megastorm scenarios capable of causing a megaflood in California.
"We assess the cumulative and annual likelihood of a 30-day megastorm sequence capable of causing a California megaflood and find that both increase strongly as a function of climate warming.
"We find that the annual likelihood of an ARkHist level event increases rapidly for each 1°C of global warming [by ~0.012/year per degree C from a baseline of ~0.01/year]; Fig. 5B) and that this approximately linear relationship (P < 0.001) appears to hold even at very high levels of warming (~+4°C)."
Only about 1% of properties in the hardest-hit counties of the state have federal flood insurance, government records show, and general homeowners insurance policies don't cover flood damage.
The Kentucky communities suffering from the damage are especially ill-equipped. They include some of the poorest counties in the U.S., with little funding for rebuilding or flood resilience projects. ■
A clipper system will move quickly across the northern Plains into the Midwest Friday and the Northeast by Saturday, bringing a wintry mix of rain and snow showers ahead of a sweeping cold front.