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Sinking landscape, rising sea level, and now rain: into each life on the Gulf coast a whole lotta’ rain must fall.

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by Len Bahr, Ph.D.

Fig. 1. Harvey rain

Fig. 1. Harvey rainfall totals and distribution.

On August 31, The Washington Post published a report by weather editor Jason Samenow, asserting, without equivocation, that Hurricane Harvey and the deluge that it spawned resulted in a 1,000 year flood event, in this case exclusively from rainfall. Figure 1 illustrates the huge footprint of this disaster.

Here’s a quote from Samenow’s article:

There is nothing in the historical record that rivals this, according to Shane Hubbard, the Wisconsin researcher who made and mapped this calculation. “In looking at many of these events [in the United States], I’ve never seen anything of this magnitude or size,” he said. “This is something that hasn’t happened in our modern era of observations.”

I’m extremely cynical about the 1,000 yr expected return frequency of this event, given that Houston is said to have suffered three 500 year flood events in the past three years. At any rate, reading about the scale of this disaster and the fact that flooding was all from rainfall, led me to an internet search for normal precipitation patterns in the lower 48 states, which turned up Fig. 2, by Christopher Wray, who created the graphic using 1981-1990 data.

I was surprised to see that the northern Gulf coast, which we recognize as increasingly vulnerable to flooding from wind-driven storm surge, is also ground zero for the highest mean annual rainfall in the continental U.S. The 30+ inches of rain that fell during two days in August, 2016 in the Baton Rouge area — an all-time record for Louisiana — occurred in an area that easily accommodates a base level of 60-70 inches/yr. Houston’s recent 50 inch rainfall, doubling its background range of 40-50 inches/yr, is presumably far more exceptional. On the other hand, both the Baton Rouge and Houston events were strongly influenced by a steadily warming Gulf since 1990 and by unmitigated land development in and around both cities,

Fig. 2.

Fig. 2.

On September 3 the NYTimes published an article by Nicholas Kristof on the climate change implications of Harvey, including the following striking quotes:

Last year was the third in a row to set a record for highest global average surface temperature, according to NASA. The 10 years of greatest loss of sea ice are all in the last decade. 

…The truth is that what happened in Houston was not only predictable, it was actually predicted. Last year, ProPublica and The Texas Tribune published a devastating article about Houston as a “sitting duck for the next big hurricane” and warned that Texas was unprepared.

On the currently heated subject of flood risk, on September 3 Nola.com | TheTimes-Picayune published a highly persuasive op/ed by Bob Marshall on the failure to purchase flood insurance by 85% of the flood victims in Houston, many of whom could have afforded it but didn’t see the need.

The inescapable logic of Marshall’s piece is that homeowners in South Louisiana* with sufficient means to purchase flood insurance should be required to do so, especially in increasingly high risk areas. Nevertheless they won’t, because their elected officials, shamelessly beholden to Donald Trump’s real estate industry, will not toughen the law. According to Marshall, the decision to buy flood insurance in hurricane (and rainfall) alleys is no less rational than buying medical, automobile or homeowners insurance. The fact is that the NFIP, scheduled for renewal at the end of this month, is broken beyond repair, as documented by flood insurance expert J. Robert Parker in an opinion piece posted in TheHill on September 4.

An August 31 article by Will Oremus in Slate.com discusses the arcane and highly controversial methodology of evaluating the risk of future Harvey-scale disasters. A related article by Robinson Meyer in TheAtlantic.com reports on the folly of draining the coastal swamps, so to speak. This article focuses on a new study by a scientist named Michael Beck with The Nature Conservancy (TNC) who is unrelated to a coastal colleague of mine who bears the same name.

On September 1 Resilience.org published an article entitled: 1,200 Dead; Up to 41 Million Affected in Asian Flooding By Andy Rowell, originally published by Oil Change International. Southern India, Nepal and Bangladesh have all been ravaged by rainfall.

On September 2, MotherJones.com published an article by Adam Rogers that described the Hobson’s choice faced by engineers during the massive rainfall in the midst of Harvey’s stalled downpours who were forced to release water from two reservoirs upstream from Houston rather than to see the structures fail, causing even more catastrophic flooding of the city and its environs. The article uses the term probable maximum flood (pmf) a relatively recent statistical concept still not determined for Houston, with its indeterminate watershed caused both by development and climate change. This September 5 article by Maggie Haberman-Bosch in fivetirtyeight.com illustrates some of the difficulties faced by flood risk projections, where historic data are limited and land use changes have been dramatic.

Finally, how ironic that the struggle to cope with the most extensive flood in northern Gulf history coincides with: (1) Hurricane Irma, the most powerful Atlantic hurricane ever seen, which is now threatening Puerto Rico and southern Florida; and (2) the largest wildfire in Los Angeles history. Are you listening Louisiana GOP officials?

*Including homeowners in coastal areas subject to rainfall flooding, such as EBR Parish, that are inexplicably excluded from coastal planning. .

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  1. Walt Sikora says:

    The great Houston flood of 2017 was a so-called,”1000-year flood event” however, it was caused as much by human stupidity as by Hurricane Harvey. First of all, it seems that people evidently don’t believe in science and seem to think that scientific evidence and results are just the opinions of those elitist scientists. This attitude represents the total failure of the American concept of a liberal education. Instead of teaching how to think critically, children are thoroughly taught their “rights” and everybody in this free country has the right to his own opinion, even if it flies in the face of historical as well as scientific evidence. So it’s no wonder that elected and appointed officials like Trump and Pruitt get away with calling global warming a hoax.
    Scientists have known for a long time that the entire Houston area, and beyond, was an ancient, shallow sea bottom with the result that the land is table-top flat with a slope of less than one foot per mile. During the Eocene Epoch, all of southeast Texas was covered by a shallow sea up to and including as far north as Bryan/College Station. This time period is also known as the Paleocene/Eocene thermal maximum (PETM). All indications are that we are headed toward those same conditions again.
    Houston has also been the “poster-child” city with regard to urban sprawl, yet, because of the Texas Builders Association, Houston doesn’t have any zoning ordinances. Can you believe that? Of course the developers make their money and run, and the elected officials like it that way, because property taxes are the major government income source, since Texas doesn’t have an income tax. Just Check out this Bloomberg article- “Harvey Wasn’t Just Bad Weather. It Was Bad City Panning”

    https://www.bloomberg.com/news/features/2017-08-31/a-hard-rain-and-a-hard-lesson-for-houston

    As if all this lack of planning wasn’t bad enough, the fact is, it has all happened before. The city of Houston was founded, in 1837, and since 1839, two years later, until mid-2007, there have been 210 “significant” Houston area floods according to the Weather Research Center.

    http://www.wxresearch.com/almanac/Texas/houflood.html

    • Open http://www.hurricanescience.org and bring up hurricane Camille in the 1960s. Did Camille really have 190 mph sustained winds and a low pressure of 905 mb? Could hurricane Irma be a Black Swan event?
      CS

      • Coastal Whiz Kid says:

        Irma had the highest sustained winds and lowest central pressure ever recorded for “an Atlantic Ocean” storm. Camille was a Gulf of Mexico event (as was Wilma, who I think surpassed Camille). the warmer waters of the Gulf of Mexico are the reason Gulf hurricane tend to be more intense than Atlantis storms.

    • Editor’s note:
      Walt Sikora is an old friend and colleague who now lives in Athens, Georgia, where I met him in the late 1960s. At that time his then future wife Jean and I were fellow doctoral students of coastal ecology at the U. of Ga.
      During the late 1970s as an LSU Marine Sciences faculty member I had the opportunity to recommend the hiring of Drs. Jean and Walter Sikora as part of a USACE-funded team study of Lake Pontchartrain, led by Dr. Jim Stone. We studied the ecological state of this huge estuary and Walt and his now late wife Jean assessed: (1) the “health” of the benthic community of the entire lake bottom; and (2) the disastrous impacts on the lake ecosystem of the politically powerful clam shell dredging industry, which was essentially paying off our Department of Wildlife and Fisheries in order to stay in business.
      The Army Corps prematurely pulled the plug on the Pontchartrain study in 1982 but the Sikora reports were later published (references needed) to play a telling role in the eventual prohibition on shell dredging in coastal Louisiana, that was signed in 1999 by my boss at the time, Gov. Mike Foster http://lacoastpost.com/blog/?p=47518. The sordid story of shell dredging in our state was documented in a fascinating Tulane Law Review 2012 monograph by Professor Oliver Houck https://biotech.law.lsu.edu/blog/The-Battle-of-Lake-Pontchartrain.pdf.

  2. WOW! Mr. Taleb’s MIF reminds me of the model being used for the river diversions which is a MUFF.

  3. One of the significant considerations above is the challenge to “analyze climate change through the lens of minimizing risk, rather than maximizing utility.” But which kind of risk should be analyzed? Most risks are viewed in the light of statistics in general and statistics of normalized distributions (bell-tapped curves) in particular. This use of actuarial “science” is totally inappropriate for extreme events of any kind because the first thing you do to use statistics on a population is to throw out the extremes.

    Engineering practices relating to extremes, such as space flight, don’t consider what “might” happen but consider what “can” happen. Engineers use representative “scenarios” or “worst cases” rather than statistical measures to characterize areas of concern. These practices are collected under the name of “Black Swan” investigated by Nassim Taleb https://en.m.wikipedia.org/wiki/Black_swan_theory to explain and address both past and future extreme events across all disciplines. As an analytic framework, Black Swan yield superior insight in extreme events of all types including weather related phenomenon. This is in sharp contrast to abject failure of actuarial methods to anticipate or prepare for recent extremes. The condition of three 500 year event in three years reflects this absurdity

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