Tuesday, November 20, 2012

It will blow away again

kw: agriculture, irrigation, natural disasters

For the past two evenings we watched The Dust Bowl (in 2 episodes) on PBS (WHYY). The core of the first episode was the plowing up of the buffalo grass sod, and that made the land vulnerable to being blown away when the inevitable multi-year drought came, starting in 1932. The nation didn't take much notice until a dust cloud crossed the nation in 1935, piling Kansas and Nebraska and Dakota dirt onto Chicago and New York and upon the decks of ships 300 miles out in the Atlantic. The second episode largely covered the migration of the "Okies" and the gradual recovery once the drought broke, albeit with agonizing slowness.

This image shows central Cimarron County, Oklahoma as it looks today, centered on Boise City (pronounced "boys"). The personal stories recorded by Ken Burns took place in Boise City and nearby places. Though the area subject to drought shifted from year to year, Cimarron County was affected every single year of the disaster.

The green dots seen in this October, 2011 satellite image are fields irrigated by center-pivot systems. The squares are irrigated by other means. All are watered by mining the Ogallala Aquifer. Most of the aquifer's storage is in Nebraska. Irrigation has kept the land covered by vegetation, staving off dust blows during droughts.

As a whole, the aquifer has been depleted by 10% in 60 years. That doesn't sound like much, but half of that is in the past 15 years. Current rates of depletion greatly exceed recharge, which is primarily via the Sand Hills of northern Nebraska and southern South Dakota, an area that receives only 10-12 inches of precipitation yearly (Cimarron County receives about 18).

Further to the east, in central Oklahoma, where we lived for nearly 10 years, rainfall totals 30-32 inches yearly. It was still hard to grow large trees there; we had a few smallish trees in our yard, less than 30 feet. The only areas you saw large numbers of 30-40 foot trees was along streams. In more humid areas of the country, such as the Mid-Atlantic where we live now, with 40+ inches of rain yearly, trees grow 60-100 feet.

The area in the upper left of the image is mostly natural grassland, over an area too rough or steep to plow. This area didn't "contribute" to the dust bowl, but dust blowing through from other areas made it impossible to keep cattle alive even though there was grass to eat. The natural use of this whole area is grassland and can support livestock if the natural grasses remain intact. The irrigated areas, instead, produce wheat or other water-thirsty cash crops. The time will most definitely come that this will end. Will there be a way to restore grassland then?

The OK-panhandle/TX-panhandle area is expected to get even more dry as the climate warms. Farmers and ranchers have been able to ride out more recent droughts by buying more water or drilling more deep wells into the Ogallala Aquifer. Another 5- to 8-year drought like the 1930s is certain to happen again. If climate warming settles in for a longer term (think decades), a mere 5-year drought will seem like "good old days". Wish I had a solution…

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