Tipping points

It’s late July, and the summer rains remain few and far between.  By now, we’d hope to see a five-day forecast fully populated with Thunderstorms Likely icons, and a few Severe Thunderstorms thrown in for good measure; instead, we’re having to hang our hopes on days when the prognosis tips to Scattered, rather than Isolated, storms.  

Out here in the southwest and Rockies, we count on these summer rains—all of us do: piñon, cougar, deer mouse, side-oats gramma, cooper’s hawk, swift fox, human, bobcat, and bunny. In a good summer, we’d get close to half our annual allotment of eleven or twelve inches of rain between the 4th of July and just after Labor Day.  But those good years are slowly becoming exceptional, no more than one year of five.  Much more common are feeble rainy seasons like this one, two or three of every five years.  In July here in Cañoncito, we had one half-inch storm and a couple of close-to-quarter-inch ones.  There’ve been years when that would have been a typical week!

IMG 9881This is what climate change has been predicted to look like in the southwest.  The future’s here.  (Oh, were that so….we’re just a few steps along that new road, in fact.)

Driving along the Front Range of the Rockies from Denver last weekend, I got a regional look at this summer moisture pattern, a three-hundred mile Big Picture within which my five-mile-wide dark cloud and lightning vigil takes place each day.  It was not a pretty picture.

Actually, it was too pretty a picture: nearly all the mountains along the way stood clear and tall from their jagged peaks down through folded forested ridges to the plains at their feet.  Beautiful!  And just not right for a midsummer late afternoon.  In only two fairly small (ten-mile wide) areas were the mountains socked in, the dark, dark bottoms of towering cloud masses 

reaching down below treeline, disgorging precious moisture into a watershed or two while the peaks were enveloped in powerful waves of thunder, rolling across tundra bowls and glacial lake basins after each piercing bolt of lightning….Oh, the beauty and power of our summer storms!  But as I travelled south along the western edge of the Great Plains, the clouds above the mountains to my right remained well above the peaks, billowing only gently, devoid of towering thunderheads, let alone one of those awe-inspiring anvils spreading high and wide with yet another burst of moisture-filled air lunging up through its topside into the sky above.  No, I drove for six hours through a tranquil sky-scape in which the small cumulus clouds that rose above the mountains broke up and dissipated as they reached the plains, melting nearly away within a few dozen miles to the east.

The mountains were doing their best to fulfill their given role of wringing  some of the moisture out of the air arriving from the Pacific after a journey across the Great Basin and the canyon lands of Utah and northern Arizona.  As morning sun warmed mountain valleys and ridges, the continental air mass traveling east was lifted by the rising heat and the rising lands below, moisture condensing into those welcome summer clouds.  So far this year, though, this daily cycle, this diurnal pulse of cloud-making, hasn’t hit the tipping point.  We wait, we watch, we hope, we pray, each summer the same anticipation, the same longing—for the week when “the rains come.”

We wait for that big rain one day, thunderheads disgorging their innards before the clouds melt away sometime between sunset and the wee hours of the night.  The next morning’s sun blazes down on the soaked earth, coaxing some of yesterday’s moisture to rise from trees and soil, and by late morning, it’s coming together into widespread healthy cumulus, which join together through mid-day into billowing thunderheads.  From any spot on the high desert, we might see three, four, five storms building into sure-fire afternoon and evening downpours, each of which will soak an expanse of land (thirsty land laced with roots and rivers eager to receive this precious rain) and provide new moisture for tomorrow’s evaporation/condensation/precipitation cycle. 

Each year, we watch the skies, our thirsty animal bodies awaiting this subtle tipping point, after which our arid, sun-drenched landscape becomes – for a few glorious weeks – the trigger and receptacle for this daily dance of moisture into and through and down from the expansive sky we also love so well.

But.

We don’t always reach this tipping point.  A half-inch rain disappears into the parched soil, the next day’s sun finding little moisture to release.  Each day that follows, the soil dries ever more, so what clouds do form don’t hold enough moisture to grow into “real” storms; instead of a couple half-inch rains followed by an inch or a steady diet of quarter-inchers, we get a spit (.07 inches feels so much better than none!) followed by several days of no rain at all.  Once a week, twice when lucky, a little something falls from the sky in any given spot across this vast expanse of high desert, piñon-speckled hills, and prairie fringe.

The picture I saw along the front range was of the system tipping the wrong way: more moisture being pulled from the soil by each morning’s sun than is returned by the Scattered or Isolated afternoon and evening rains.  It was a pitiful sight, the clouds dissipating over the plains, the grasses still mostly yellow and brown rather than greened up, and out there to the east, the story repeating: not enough moisture making it out onto the plains to fuel the typical build up of even more massive anvils with resurgent billowing towers of moisture-and-heat-cycling power, those plains thunderheads that glow pink far to our east at sunset.

And of course, the deficit of moisture heading east is multiplied in this way to become the near-epic crisis across the American agricultural heartland, now facing its worst drought-driven crop failures in decades (see current NOAA drought maps).  Omaha received just one one-hundredth of an inch of rain in July.  The only tattered shred of silver lining to come from all this is the news that the oxygen-depleted dead zone in the Gulf of Mexico is less than half the size of last year’s, and the fourth-smallest since the zone appeared in the 1980’s.

Cycles of energy can be so sensitive—what does it take to tip this moisture cycle into our gratefully-received summer rains, or into a near-miss of increasing aridity?  It occurred to me that all we need, at some point each July, is just a bit of surplus moisture riding in from the Pacific or the Gulf of Mexico (yup, sometimes it slides up from down there), a pulse of water from afar that can be wringed from the air by the mountains, soaking the land and initiating the virtuous cycle of summer rains.  Conversely, if such a slight surplus never arrives, or more disruptive, the incoming air is already drier than average, the best efforts of sun and mountains to get the moisture cycle going can come up short, or spiral down under the hot sun into a deeper aridness.

Watching the clouds melt away back into blue sky over the plains, and seeing the modest cumulus above the mountains unable to ramp up into the rain givers, my thoughts turned also to our society and how the middle-class nourishment cycle has dried up over the past thirty years or so.  For those climbing the rungs of society’s ladder, there once was the possibility of a slight surplus of opportunity to ripple through their lives: state colleges with minimal tuition, the GI Bill for many, factory jobs that paid enough to set some savings aside, a cost of living modest enough that starting a small business carried a level of risk within reach of more Americans of modest means.  Oh, hard times could still come through, as well, but there were far more options for picking oneself up without taking on outsized debts.

The dynamic influence of a slight surplus – a bit more than “just enough” – can make all the difference in tipping a life, a society, an ecosystem, into a cycle of increasing prosperity.  As conversely, a slight deficit – not quite enough – can leave both plants and people withering, hanging on in harsh conditions, unable to prosper. 

I’m sure my highway musings, on both the moisture cycle of the American west and the drying up of economic opportunity in American society, are oversimplifications.  Yet we know tipping points are real, and perhaps the life of the clouds and sky and sun and soil is not so very different from the life of the heart or the life of a society.  A little extra, available at key moments, can go a long way.

About Jim

Night sky watcher; a mobile bit of earth's body. One foot lingering in Lower Cañoncito's piñon-juniper foothills at the southern tip of the Rockies, the edge of the Great Plains stretching away from the mouth of our little valley a couple miles downstream. The other foot re-rooting into the Land of the White Pines, home of my blood and bones, amidst the coastal plain and glacial hills and ponds of southern Maine, between the North Atlantic and the bones of the ancient Appalachian Mountains.

Posted on 2012/08/02, in Earth, Jimwords. Bookmark the permalink. 1 Comment.

  1. Beautiful, Jim. Thanks for sharing your tremendous insight into rain and what you can tell about it by using your powers of observation. It’s amazing how much we need it to survive and how viscerally discomforting it is to be without it.
    Melanie

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