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Author Topic: The 100th Meridian aridity line: is it really moving east?  (Read 429 times)

John Batteen

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I live in north central South Dakota around 98.9 degrees west.  My personal experience on the ground indicates that, at least up here, the line is not moving east.  If anything, it is moving west.

Now, this may just be a temporary phenomenon.  The northern plains have an extremely variable climate.  There really is no normal.  We go in cycles, sometimes up to several decades long, where a given trend will stick around.  Ridiculously snowy winters come and go.  Wet and dry summers come and go.  Cold winters come and go.  I attribute this to being directly in the center of the North American continent, and thus subject to all the various weather patterns controlled and moderated by the oceans at the edges of the continent doing battle in the middle.

That said, it's stuck around for a while now.  Back in the late '90s, we had a bunch of fairly wet years together, along with the infamous winter of '96-'97 where it snowed SO MUCH.  Minnesota residents might remember the Halloween blizzard of '96.  It had already moved over us by the time it was time to go trick-or-treating, so my parents were able to safely drive me through temperatures approaching 0f to go trick-or-treating in the mall.  Anyway, spring '97, all that snow melted and made a bunch of new lakes that never went away.  They are still there today.  The state had to spend millions of dollars building up roads that now went through lakes.  That's why, if you're ever driving through NE SD and wonder why in the world they went through all the effort to make a road through a lake, they didn't.  The road was there first.  And once the lakes formed, there was no other way to get where that road went.

We have had an occasional dry year or three since then, even hitting D3 or D4 on the drought monitor, but that's normal for us.  The drought monitor measures soil moisture relative to average, but does not take into account standard deviation, which is huge here.  After those dry years those lakes never went away.  Now especially since ~2010, much like in neighboring MN, we have been getting much, much more humidity in the summer.  This reduced envirotranspiration as well as enhanced precipitation.  We historically averaged 17" of precipitation a year.  The latest 30 year average from 1980 to 2010 is 20".  It will undoubtedly go up when they refigure for 2020.

2019 was both the wettest and snowiest calendar year on record, with 30.35" total yearly precip including snow water equivalent, and 97.3" of snow, in Aberdeen.  We set a few dewpoint records last year too.  This is in a historically semi-arid climate.  Prickly pears grow here.  Or at least they did, until they probably all got drowned out last year.  Again, a whole bunch of new lakes formed that have not gone away.  This time, one even formed on our farm.  I'm thinking of stocking it with fish if it doesn't go away this summer.

Most climate models agree that we will get wetter, however the increases in temperature are expected to offset those increases and still lead to an overall increase in evapotranspiration.  So far, that does not appear to have occurred.  Increases in summertime humidity if anything have decreased it.  So, what are we looking at going forward?

There are a few factors.

One.  Possibly, we are just in a long multidecadal wet cycle, and it will get dry here soon enough.  Very possible.

Two.  The models failed to account for the expansion of King Corn's domain, and massive fields of corn are responsible for the significant dewpoint increases we've seen.  This is sort of a side effect of roundup ready corn.  When I was a kid here, no one grew corn or soybeans, they all grew wheat, sunflowers, barley, oats, rye, millet, sorghum, that kind of thing.  Cultivation and tilling and plowing release a great deal of moisture from the soil into the atmosphere with each pass.  Having to go over each field many times a year for weed control lost lots of moisture.  Now, they only have to till going from corn to beans, and even then, not all the time.  No till from beans to corn, and of course, no cultivation during the growing season either since all weeds are controlled by sprays.  You see spring wheat or sunflowers every now and again these days, like 1%-5% of fields in this area, but the rest is all a corn/soybean rotation.  So that corn transpires a lot of water, and as corn's range extends west upwind of us in southern SD and Nebraska, we are getting their evaporated corn water triggering thunderstorms up here.  Corn has been shown to increase local dewpoints from 5 to 15 degrees fahrenheit.  I think actually that overall, agriculture is a poorly understood influence on global climate that is probably underestimated.

Three.  The models failed to account for the increase in plant water use efficiency due to elevated CO2 levels, and while the climactic evapotranspiration line may indeed move, it may do so independently of the plant life.  We have found already through satellite imagery that, independent of yearly precipitation variation, the world's deserts are greening due to CO2.  The more of a water deficit a biome operates at, the more sensitive the plants are to CO2.  This is because the plants must open their somata to absorb CO2 for carbon to build their structures, but in so doing, they lose water at the same time.  Higher CO2 concentrations mean plants lose less moisture in acquiring the same amount of carbon.

I think point number 3 is already having noticeable effects in semi-arid agriculture.  While 2019 was wet, both 2017 and 2018 were major droughts.  D2, D3, areas of D4 popping in and out through the summer.  And they still harvested a halfway decent corn and soybean crop here even so.  I don't live in town, I am surrounded by crops as soon as I leave my house, and I spend a lot of time outside gardening.  I watched those crops all summer long, thoroughly convinced from April through July that they were dead men walking, going to die any day now.  No way they could keep alive through all of this.  All this stuff is dryland, we don't have irrigation here.  2017 hit 100 a couple times and 2018 we went over 100 5 times and hit 105 once.  An inch or two of precip a month both years, usually in one big storm a month that came with the fury of Thor and did a lot of damage with high winds and hail.  But live they did, and the farmers made money.  Nothing short of amazing.  I do know they are breeding drought tolerant corn and beans, but all the same, I mean, you just had to see it for yourself or you wouldn't believe it.  It wasn't just hot.  The plains are windy, almost all the time, and often very very windy.  You've probably seen the Wyoming Wind Sock.  We evaporate a LOT of water.  It can't just get 105 here without a stiff, stiff SSW wind pumping in air straight from the desert before it has a chance to cool down.  The best you can do in calm air is typically mid 90s.  What I mean to say is the wind was stiff out of the southwest all summer long.  We had several dust storms in 2018 like what you saw pictures of from the great depression.  It got dark enough the photosensitive nighttime light in the driveway turned on.  None of the farmers are afraid of drought anymore, because they all say only half jokingly, "well we learned in 17 and 18 that you don't need moisture to grow a crop."  Just absolutely incredible and I don't have any other explanation for it.

Four.  Things I'm not thinking of.  Do you have any idea what they might be?

I don't really know what to expect in the next 100 years.  Especially considering the region naturally oscillates between dry and wet on long and short timescales.  https://www.unl.edu/plains/fritz.pdf is a great paper on the recent history of plains droughts.  But that was in a relatively stable climate.  Now everything is changing.

Anyone else living near the meridian at other points that can comment on their experience on the ground?
« Last Edit: May 28, 2020, 01:33:54 AM by John Batteen »

oren

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Re: The 100th Meridian aridity line: is it really moving east?
« Reply #1 on: May 28, 2020, 04:53:42 AM »
I can't comment on the subject, I live about as far away from the Great Plains as possible, but I must say this was an extremely interesting eye-opening post. Well Written.

sidd

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Re: The 100th Meridian aridity line: is it really moving east?
« Reply #2 on: May 28, 2020, 07:36:45 AM »
I take it this is in reference to doi: 10.1175/EI-D-17-0011.1 and doi: 10.1175/EI-D-17-0012.1
Open access, chekitout.

Seager used CMIP5, might be good to revisit with CMIP6.

That said, i was out in South Dakota last year summerish, and i saw the badlands green. I am told it happens, but I had never seen that before, quite wonderful. Millions of butterflies. I posted some pics somewhere on this forum at the time. This was just after the big missouri river floods and i saw a lot of standing water about.

I usually am east of the mississippi but i venture out west now and then every couple year or so, and Mr. Batteen's observations coincide with mine. I usually stop in lakota sioux territories and make it a point to talk, and in my experience they agree, the way they put it is interesting, "the water is sweeter."

However, anecdotes are certainly not data.

sidd

sidd

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Re: The 100th Meridian aridity line: is it really moving east?
« Reply #3 on: May 28, 2020, 07:53:51 AM »
Re: as far away from the Great Plains as possible

Holy shit ! What's Kerguelen like ?

sidd

oren

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Re: The 100th Meridian aridity line: is it really moving east?
« Reply #4 on: May 28, 2020, 08:30:35 AM »
Lol, my bad. Kerguelen is almost double my distance...