Saturday, March 28, 2015

Chile: Driest Spot On Earth Suddenly Gets Very Wet

Severe flooding this week in Capiapo, Chile.
Photo from Aton Chile.
If you live in especially the damp eastern half of the United States or the Pacific Northwest, and you get an inch of rain in a day, that's really not a big deal.

An inch of rain in 24 hours definitely makes for pretty rainy, sopping wet day, but it's not exactly scary.

But if you live in Antofagasta, Chile, in the Atacama Desert, an inch of rain is basically the Biblical 40 Days and 40 Nights.

That desert town indeed got nearly an inch of rain in 24 hours at midweek.

Because the landscape there is not used to such rains, there was some devastating flooding.

The normal dryness in this Chilean desert is remarkable. The town of Antofagasta on average gets about 0.07 inches of rain per year, so that storm of nearly an inch is basically almost 14 years' worth of rain in a day, notes Dr. Jeff Masters on his Weather Underground blog. 

For perspective, many cities on the United States East Coast get, on average, between 35 and 40 inches of rain per year, or about 500 times the amount Antofagasta, Chile typically gets.

This Chilean desert region is normally so dry for two major reason. The Pacific Ocean off Chile is normally, well, chilly.  The cool ocean stabilizes the air, preventing the kinds of updrafts that can cause rain and thunderstorms. So it's dry.

California is dry like that in the summer for much the same reason.

Also, the very tall Andes Mountains form a huge barrier between the Chilean coast and the Atacama desert. What little moisture can arise from the coastal regions can't make it over the mountains.

So, the Atacama Desert is a barren moonscape, dry and devoid of almost all vegetation.

That this desert got all this rain suddenly is a sure sign that an El Nino is underway. El Nino is that weather pattern that warms the eastern Pacific Ocean and can disrupt weather patterns in much of the world.

The eastern Pacific ocean touches Chile, so that patch of water is now much warmer than usual. Warmer water is more conducive to the updrafts that can cause those thunderstorms and rains.

On top of that, an area of low pressure moved north to near the Chilean coast. Such low pressure systems, originating from near Antartica, don't usually get that far north, but this one did.

That weather system added even more lift to the atmosphere, further encouraging rains. There was so much rain and wetness that some of this excess moisture was able to move up and over the normally inpenetrable Andes, so it poured in that dry desert.

Severe flooding hit other parts of Chili as well, reportedly leaving seven people dead and 19 missing, Reuters reported. 

Neighboring Peru got hit by severe floods, too. It was also unusually warm in many of these regions. The highest mountains usually receive snow instead of rain, but even on the peaks, it rained. That contributed to the flooding.

Here's a dramatic video report from the BBC:

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