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What Past Droughts Tell us about Tomorrow

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Lake Powell, in 2009, showing a white calcium carbonate “bathtub ring” exposed after a decade of drought lowered the level of the reservoir to 60 percent of its capacity. (Photo courtesy of U.S. Bureau of Reclamation.)

The West without Water: What Can Past Droughts Tell Us About Tomorrow?

by B. Lynn Ingram vol. 8, issue 6 – March 2015 OSU.EDU

Editor’s Note:

Almost as soon as European settlers arrived in California they began advertising the place as the American Garden of Eden. And just as quickly people realized it was a garden with a very precarious water supply. Currently, California is in the middle of a years-long drought and the water crisis is threatening the region’s vital agricultural economy, not to mention the quality of life of its people, plants, and animals. This month B. Lynn Ingram, Professor of Geography and Earth & Planetary Science, examines how a deep historical account of California’s water patterns can help us plan for the future.

The state of California is beginning its fourth year of a serious drought, with no end in sight. The majority of water in the western United States is delivered by winter storms from the Pacific, and over the past year, those storms were largely blocked by an enormous ridge of high pressure. A relatively wet December has given way to the driest January on record, and currently over 90 percent of California is in severe to exceptional drought. The southwestern states are also experiencing moderate to severe drought, and this comes on the heels of a very dry decade. This long drought has crept up on the region, partly because droughts encroach slowly and they lack the visual and visceral effects of other, more immediate natural disasters such as earthquakes, floods, or tsunamis. Meteorologists define drought as an abnormally long period of insufficient rainfall adversely affecting growing or living conditions. But this bland definition belies the devastation wrought by these natural disasters. Drought can lead to failed crops, desiccated landscapes, wildfires, dehydrated livestock, and in severe cases, water wars, famine, and mass migration. Although the situation in the West has not yet reached such epic proportions, the fear is that if it continues much longer, it could.

In California, reservoirs are currently at only 38 percent of capacity, and the snowpack is only 25 percent of normal for late January. Elsewhere in the Southwest, Lake Powell, the largest reservoir on the Colorado River, is at 44 percent of capacity. The amount of water transported through irrigation systems to California’s Central Valley—the most productive agricultural region in the world—has been reduced to only 20 percent of customary quantities, forcing farmers to deepen groundwater wells and drill new ones. Over the past year, 410,000 acres have been fallowed in this vast agricultural region that provides 30 percent of all the produce grown in the United States and virtually all of the world’s almonds, walnuts, and pistachios. As California dries up, food prices might well rise across the nation.
The question on everyone’s mind is when will this dry period finally come to an end and rainfall return to normal—and just what is normal for the U.S. Southwest when it comes to rain?
And with a growing and more urban population and an ever-changing climate, will we ever be free from the threat of long dry periods, with their disruptive effects on food production and the plants and animals that rely on water to survive?

A glance into the history of the Southwest reminds us that the climate and rainfall patterns have varied tremendously over time, with stretches of drought many decades longer than the one we are experiencing now. Long dry stretches during the Medieval centuries (especially between 900 and 1350 CE) had dramatic effects on the native peoples of the Southwest (the ancestral Pueblo, Hohokam, and Sinagua), including civilizational collapse, violence, malnutrition, and forced social dislocation. These earlier Americans are a warning to us. The past 150 years, which we have used as our baseline for assumptions about rainfall patterns, water availability for agriculture, water laws, and infrastructure planning, may in fact be an unusually wet period. Let’s look at the past few hundred years first and then explore the region’s climate in geological time.

 

[excellent article- worth reading entire piece here…]

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