The epic amount of rain that led to deadly, catastrophic flooding across large parts of South Carolina and North Carolina is an example of exactly the type of supercharged storm system climate scientists have been warning about for years as a likely consequence of global warming.
This storm, like others that have come before it — from a massive deluge that flooded Oklahoma City to a flooding event in Houston, both of which occurred earlier this year — are examples of how the atmosphere is behaving in new ways now that there's more water vapor and heat for weather systems to work with.
It's not that heavy downpours and floods didn't occur before manmade global warming became evident (for the record, they did). The issue now is that these events are even more severe than they otherwise would have been. And they are becoming more frequent in many areas.
Though there are significant limits on what climate scientists can say at this point about an event like the South Carolina floods, it's well-established that global warming has already led to a measurable increase in global atmospheric water vapor levels, and this moisture can be wrung out as heavier bursts of rain or snow.
It is also well-established in scientific literature that precipitation is increasingly falling in short, intense bursts rather than long-lasting, generally lighter events.
The risk for extreme precipitation events is increasing in many parts of the world.
One study, for example, showed that a 1-in-100 year winter-rainfall event in parts of the United Kingdom is already occurring more frequently, becoming a 1-in-80 year event.
This means that an event with a 1% chance of occurring each year now has a 1.25% risk of occurring in any particular winter, which translates to a 25% increase in risk, according to Oxford University scientists.
Water vapor and the Carolina firehose
While it's too soon to say precisely how global warming may have affected the rare confluence of events that conspired to dump at least 26.88 inches of rain in less than four days on South Carolina, changes in extreme precipitation events are one of global warming's most well-documented climate change impacts.
First, consider how significant this rainfall event has been. Charleston and Columbia saw so much rain in four days that they both blew past their previous records for the all-time wettest October, along with setting numerous other milestones.
As many climate scientists will say, though, we seem to be seeing more and more 500-year to 1,000-year events lately, to the point where the definition of such events and their return intervals may need to change.
How did this happen?
There were four main meteorological players in this extreme weather event, each of which raised the odds for a record rainfall event in the Carolinas and caused weather forecasters to sound the alarm for the Palmetto State as early as midweek last week.
These atmospheric players include an upper-level low-pressure area across the Southeast; a stationary front with an area of low pressure riding along it; Hurricane Joaquin, which passed off the East Coast and moved close to Bermuda; as well as a strong area of high pressure parked across southern Quebec.
Climate change increases risk of extreme rainfall events
Across the U.S. as a whole, the frequency of 2-inch or greater rainstorms has increased in recent decades, and extreme precipitation events have been on the rise across the Northern Hemisphere as well.
A Climate Central analysis released in May found that 40 of the lower 48 states have seen an overall increase in heavy downpours (the days where total precipitation exceeded the top 1% of all rain and snow days) since 1950.
However, South Carolina was one of the few states that did not see an increase, based on that analysis. In fact, it saw a slight decrease in the frequency of heavy precipitation events. Neighboring states, including Georgia and North Carolina, did see increases, though.
No comments:
Post a Comment