The weather news of the week is certainly the almost incomprehensible flooding in South Carolina.
Hurricane Joaquin, which devastated parts of the Bahamas, had something to do with it, but not everything.
Joaquin is now headed for Europe, where flooding also occurred on the Riviera.
Let’s go Around The World.
Long Rain Train Chugs Into South Carolina — State Submerged
We’re used to daily weather that’s pretty close to the average. So when something happens that only occurs once in, say, a thousand years, it’s hard to reconcile the event with what we’re accustomed to. The deluge in South Carolina, unprecedented since before Europeans ‘discovered’ the New World, is such an event.
The average rainfall in Columbia, South Carolina is about forty-four inches per year; the rainiest month is July with about five and a half inches. On Sunday, 17 inches of rain fell in 17 hours. Rainfall tends to come in fits and starts, but this is not normal.
To put things in perspective, rainfall varies across the globe from the Atacama desert of Chile where it literally never rains to the monsoonal-rainy foothills of the Himalayas where a thousand inches fell in one year. Residents of Mawsynram, India wouldn’t lift an eyebrow at two feet of rain in a day.
Human beings have populated the earth in a way that’s compatible with the local weather. In South Carolina, houses and cities have been built in places that have never flooded — until now. The cleanup will take months and the death toll, now at twelve, seems likely to rise.
Water that inundated local waterways will return to the sea, most of it via rivers that empty into the ocean near Charleston. The inland flood threat now moves from local streams to major rivers.
What Was The Meteorological Cause Of The Flood?
Approximately 5×10^14 (500 trillion) cubic meters of rain falls on the surface of the earth every year — enough to fill ten billion Olympic-size swimming pools. The distribution of this rainfall is critical to human life on the planet. Theoretically, the rain could fall anywhere and for as long as it wants. Given the general circulation of the atmosphere, which keeps things moving, the rain is rather equitably distributed. But once in a while the atmosphere conspires to rain a lot in one place in a short time. This week, that place was South Carolina.
Hurricane Joaquin, nearly stationary near the Bahamas, pumped a lot of moisture into the atmosphere, and some of that became entrained in an easterly flow towards the coast of the US.
At the same time, an old frontal system stalled along the coast, and when the plume of moisture hit the doggedly entrenched cold air, it was lifted.
When saturated air is lifted, the moisture is wrung out because the air cools as it rises and cool air cannot hold as much moisture as warm. After several days of this, low pressure formed on the front and reinforced the lifting. It doesn’t happen very often, but it CAN happen.
Coastal Flooding And Erosion In The Mid Atlantic
The combination of Hurricane Joaquin and a strong high pressure system over eastern Canada brought long-fetch, moderate east winds along the coast from Georgia to New Jersey. Waves up to fifteen feet pounded beaches for several days. In New Jersey, beaches that had been restored after Sandy were again washed away, and many coastal communities were flooded.
Hurricane Joaquin And The Bahamas
The stalled Joaquin, essentially stationary for two days, delivered a powerful blow to the Bahamas. The extent of damage and loss of life is still not clear, but first reports were that whole towns were destroyed.
Joaquin brushed by Bermuda, but it was just a shadow of the category four storm that hit the Bahamas. Joaquin is now headed across the Atlantic to Europe and will transition to a powerful extra-tropical cyclone as it turns towards Ireland.
Flooding On The Riviera
Saturday night, storms hit the southern coast of France, causing widespread damage and twenty deaths.
October is the rainiest month in this region with an average of about 3 inches of rain. Up to 7 inches fell on Saturday night.
Persistent low pressure associated with cold water over the northeast Atlantic has produced a southeasterly flow over Europe for some time, and this brought moisture to the normally dry Riviera.
Are We Witnessing Climate Change Up Close?
Decoded Science has repeatedly cautioned that no single weather event can be positively connected to global warming. But a sufficient accumulation of such events makes a pretty good case. The slowing of weather systems has been anecdotally observed by many meteorologists. An objective criterion by which to test the hypothesis that persistent weather is becoming more common is not so easy to devise.
Recent flooding in many parts of the world is consistent with the facts of global warming: Water molecules will more easily be dislodged from the oceans; the warmer atmosphere can hold more water vapor.
Where’s the next place the weather will bog down and produce a flood, drought, or heat wave? Tell us what you see in the comments below.
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