Air made warmer by climate change is exacerbating both aridity and precipitation, leading to double-whammy weather cycles.
(Bloomberg) — In recent years, extreme storms being juiced by climate change familiarized the general public with terms like “bomb cyclone” and “atmospheric river.” Now a string of storms in California is showcasing another unwelcome weather reality of the warming world: “hydroclimate whiplash.”
After years of megadrought left the land parched, California experienced so much heavy rain so quickly that the governor declared a state of emergency on Wednesday as another storm system prepared to unload on the state. And forecasters have predicted more rain for the weekend.
Climate change helps explain both the very wet and the very dry conditions, scientists say. They predict that atmospheric rivers, like the one that descended on California earlier this week, will become more common and more costly. The storms so far have downed trees, closed roads and left more than 180,000 people without power, while also refilling low reservoirs.
“When it comes to things like extreme precipitation events and extreme heat waves, we know, essentially without a doubt, that they will increase with a warming climate, and we have warmed 1 degree [Celsius] already,” said Daniel Swain, a climate scientist at the University of California at Los Angeles.
When warmer air interacts with California’s natural pattern of aridness punctuated by rain, it essentially puts both dryness and precipitation on steroids. For example, atmospheric rivers — long, moisture-rich airflows in the sky — are not new occurrences. But the atmosphere’s capacity to hold water vapor increases exponentially for every degree of linear warming.
Warmer air explains how Northern California experienced both record rains and record heat in 2017, and why it may be set to shatter those records in the coming months.
Last summer, Swain and a colleague published a paper estimating that climate change has probably already doubled the risk of a flood event from these atmospheric rivers. And the rain is all the more dangerous because it falls on parched land with limited ability to contain runoff. Tom Corringham, a climate economist at the Scripps Institution of Oceanography at the University of California at San Diego, found last year that flood damages triggered by atmospheric river storms may triple from $1 billion a year to over $3 billion a year by the end of the century.
That leaves California with the tricky task of managing water in an era when things are getting both hotter and drier, as well as occasionally much wetter — hence Swain’s term “hydroclimate whiplash.”
“If you build more dams, those become liabilities during really extreme storm sequences,” Swain said, citing the winter of 2017, when flood waters almost caused the failure of the Oroville Dam north of Sacramento.
“We’re going to need water systems that are more flexible, that can recharge our aquifers at the same time that we mitigate flood risk to urban areas,” said Swain. “It will be challenging.”
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