Our heartfelt sympathies go out to the people of Louisiana who have suffered enormous losses of life and property in the face of flooding brought to the region in a “mega-precipitation” event. Over a period of 3 days last week, the southern half of Louisiana was inundated by more than 2 feet of rainfall that caused unprecedented flooding across all of the southern parishes. A week later, the death toll stands at 13 with at least 40,000 homes damaged by floodwaters. NTC Board Chairman and former Louisiana resident, Jeff Broberg, noted the latent effects of flooded housing in his Facebook post last Sunday:
Flash floods deceive people because when the water recedes everything looks fairly normal, soggy, but with the appearance that things can be saved and the entire community will hold on to hope that things can be restored, but, 9-12 months later when the cleaning is done and it is apparent that the programs designed to help are slow without much coverage and people, whole communities of people, all about the same time realize that the flood took it all and it cannot be restored, despite all the hard work and hope…
The broadcast news media, figuratively drowning in election year trauma and desperately seeking relief through endless rounds of beach volleyball in Rio, missed the opportunity for real journalism as the Louisiana storm inexorably swamped the towns, byways and homes of thousands of unsuspecting citizens. Even the Red Cross got it wrong, calling the flood “ the nation’s “worst natural disaster” since Hurricane Sandy“. While the “natural disaster” label keeps the legal door open for federal assistance, this little fiction perpetuates the catastrophic notion that human agency is not responsible for planetary change.
We have again failed to underscore what climatologists have been telling us since the 1980s: greenhouse gas emissions from fossil fuel combustion are driving global warming at rates that cannot be accommodated without massive relocation of human populations. To its credit, the Washington Post, in a post facto analysis, suggested some ways to improve communication between imperiled populations and the weather services. But these ideas are far too few, and too late to mitigate the current crisis in Louisiana.
Getting back to basics, whatever goes up must come down. As the surface of the oceans boil off millions of tons of water for each degree of increase in surface temperature, so too must annual precipitation increase by 5 to 10 percent to maintain atmospheric equilibrium (in water content) across the entire year. A time-lapse view (below) from the geosynchronous (GOES) satellite shows the development of the water vapor mushroom over Louisiana from Thursday through Sunday last week. This view of the water vapor in the atmosphere shows a “bloom” over southern Louisiana that broadens and intensifies for a day, then moves slowly westerly while dropping moisture
over the entire southern half of Louisiana. The slow movement of the storm system resulted in extraordinary amounts of rainfall over a span of only a few days.
What does all this have to do with trout? Taking the Root River as an example of Driftless Area trout streams, suspended sediment is the single greatest factor degrading water quality in the Root River valley. In a recent 5-year study, the annual discharge of sediment at the Root River’s Mississippi River outfall was estimated at 253,000 tons. An estimated 56% of this sediment is from re-suspension of previous sediment deposits in the stream channel including erosion from the banks and slopes adjacent to the stream. The 44% remainder is due to surface runoff from urban and agricultural land, often accelerated by paving, tile drainage and loss of wetlands. It is clear that increases in flash floods or other episodes that sharply alter the flow and discharge of these rivers severely degrade the fishing experience for humans and diminish the health and productivity of fish and the aquatic organisms that support them.
Simply put, because of global warming, the increase in frequency and intensity of summer storms across the Driftless Area of the upper midwest is extending the sediment-bearing flood season well beyond the “traditional” spring snowmelt runoff. In the Root River valley alone, flood conditions have exceeded the “once in a hundred years” benchmark four times since 2000, including the Rushford, Minnesota, flood of 2007 which exceeded the 500-year benchmark (17 inches of rain in the Rush River watershed in less than 12 hours)! Mega-precipitation (or, mega-rain) events have long been known from Minnesota. But it is important to note that nearly half of these events have occurred since 2000. Other examples from the last decade include flood events from Duluth, Minnesota, south to central Iowa. For an excellent review of precipitation thresholds, see this DNR web page.
Help the victims of the Louisiana floods: http://www.nola.com/weather/index.ssf/2016/08/baton_rouge_flooding_new_orlea.html.
To help solve the larger problem, we must all become informed of the magnitude and urgency of the effects of global climate change. Watch weather patterns locally and globally so you can more effectively communicate your concerns to public agencies and elected officials. Be sure to check on the reliability and origins of information sources in order to avoid being misled by entrenched interests. For further information regarding recent stream flows in the upper Root River valley, see our “Stream Conditions” posting. The web sites listed below provide interesting observations and scientifically sound information relating to hydrology, climatology, and water quality for Minnesota and the upper midwest:
NOAA weather satellites: http://www.goes.noaa.gov/GSSLOOPS/ecwv.html
MN DNR Cooperative Stream Gauging stations: http://www.dnr.state.mn.us/waters/csg/index.html
National Weather Service: http://water.weather.gov/ahps/
Above all, get out to your favorite streams and enjoy first-hand the beauty, diversity and serenity that often accompany flowing waters. May your efforts today help to ensure that our grandchildren will be rewarded in following your footsteps.