Extreme Highs and Lows: Climate Change and the Missouri

Since the end of the last ice age, the Missouri River has experienced extreme fluctuations in volume.  The Missouri has always bounced up and down because the weather across the Great Plains quickly shifts between hot and cold and between bone dry and monsoonal.

Since last year, Missouri Basin residents have witnessed firsthand the river’s capricious character.  In June 2011, the Upper Missouri (the river northwest of Sioux City) hauled an astounding 13.8 million-acre-feet (MAF) of water.  Never before, in 114 years of recording keeping, had the Upper Missouri carried so much water in one month. By the end of 2011, a total of 62.3 (MAF) entered the Upper Missouri.  That equaled two and a half times the upper river’s normal annual runoff of 24.8 MAF.  Last year’s runoff shattered the previous high flow record of 49 MAF, set back in 1997.

This year, valley residents experienced an altogether different river.  Last month, the upper river’s inflows amounted to a paltry 285,000 acre-feet.  That was the lowest runoff ever recorded for the month of September.  The Army Corps predicts the Missouri’s total runoff in 2012 will equal 19 MAF, or less than a third of last year’s total discharge.  The reason for the low runoff is the ongoing drought gripping the Great Plains.

We know the Missouri has always gone up and down.  But what is different about the river now is that it is jumping up higher and dropping down lower than ever before.  We have had the highest monthly flow rate and the lowest September flow rate in recorded history in just the past 16 months.  This is a very disturbing trend.  It means the Missouri is becoming a wilder, less predictable, and more dangerous river.  The Corps has long tried to keep the Missouri caged behind riprap.  (By the way, the Corps loves rock.  It believes nearly every hydrological problem can be solved with more rock).  But this new, erratic river is going to increasingly defy the Corps’ efforts to not only manage it, but to contain it.

In April 2011, the Bureau of Reclamation released a report that examined the future effects of climate change on the Missouri’s hydrology.  The Bureau concluded that increases in annual precipitation across the northern plains would result in a corresponding increase in the river’s mean annual runoff at Omaha of 9.7% by the 2050s and 12.6% by the 2070s.  Remember, the mean is only an average.  The river’s maximum runoff for any given year in the 2050s and 2070s could be far higher.  Additionally, warmer temperatures in the winter months will cause a jump in the river’s wintertime discharge rates.  Finally, the Bureau stated that the Missouri’s flow regime in the 21st century would be more haphazard, with greater oscillations in volume.  The report stated, “…stream flow variability over the basin is expected to continue under climate change conditions…future hydro climate conditions may produce weekly acute runoff events….”  The term “weekly acute runoff events” is a benign way of saying the Missouri is going to flood on short notice.

Now you would think that the Bureau’s report, the flood of 2011, and the drought of 2012, would have set off alarm bells at Corps headquarters.  But surprisingly, and inexplicably, the Corps has done very little to address climate change along the Missouri.  As a matter of fact, it is actually taking steps that will exacerbate the negative effects of climate change on the river.  For instance, since last summer, the Corps has rebuilt the lower valley’s levee system.  In an act of utter folly, the new levees were rebuilt at the same locations as the old levees.  The old levees sat too close to the Missouri.  As a result, the old levees compressed the river’s flood flows, forcing the river up and then over the tops of the levees.  The new levees are going to do the same thing in the decades ahead, especially with higher flows predicted to descend the river.

To make matters worse, the Corps is rebuilding the lower river’s navigation channel.  That channel increases the likelihood of floods because it reduces the lower river’s conveyance capacity. The Corps should be increasing the lower river’s conveyance capacity, not reducing it!  Finally, the Corps has not altered its management of the upstream reservoirs in the face of climate change science.  Just this year, it precipitously drained the reservoirs to keep a nine-foot depth in a navigation channel that carries almost no barge traffic.  So it is business as usual at the Corps.  Meanwhile, we just had the third hottest summer in U.S. history.

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