What Are The Odds of “Houston, We’ve Got a Problem”?

What Are The Odds of “Houston, We’ve Got a Problem”?

It is very important to those concerned that we get the odds right on what occurred in the superstorms of the last three years in Houston. Are they an indication of a new normal on climate or meteorology? What Science and Statistics finds out may well determine whether people want to rebuild in the same spot. It may break through the Texas and Administration’s ban on considering any climate science, any planning or alterations for extreme events, or anything that might cross the interests of the Oil is King nexus that is Houston, and the Administration.

As usual, I am not an expert in any of these fields, but I do like estimating naive probabilities.

The thing that made Harvey unique is that it hung around for most of a week. This is because the Jet Stream from the West, that would have blown it Eastward, was pushed away to the North, letting the storm stay over the same area for a week. Another possibility is that the same high pressure area over California was also over Texas, and held back the winds.  Is this becoming a higher probability event, since the polar vortex jet stream has been affected by climate change?  Or because California had a five year drought from the persistent highs?  The other factors causing the Hurricane are standard: summer Gulf temperature of 87 degrees F that can rapidly increase the Category of a storm, several hurricanes spawned each season, the broad swath of Gulf coast that can intercept broad hurricanes, and a storm surge that stops rainwater from rapidly draining.

The 2015 and 2016 storm and floods were not lingering events, but mostly single day events. In 2015 there was 15 inches in 24 hours, with most of it in a 10 hour period. In 2016, there was 12 inches in 10 hours. Both these amounts of rain were categorized as a one in a hundred year event, or, their probability of occurring in a given year is 1/100. The biblical week-long inundation of over 50 inches in the Harvey rain week is considered a 1/1000 event for any one year.

In practical use, for flooding and insurance, it is not the inches that fall that count, but the areas of housing and businesses that eventually get flooded that count. So even if the climate remained constant, since Texas and Houston have abominable, Armageddon-like laissez-faire building practices of covering over swampland to build new areas, the flooding probabilities increase dramatically and rapidly, and this is what is important for reinvesting, repairing, rebuilding and designating flood zones. Even when Texas and Houston, the nation’s fourth largest city, has flood mitigation requirements, they are often ignored, and not enforced. The Trump Administration and Congress that run the Federal Flood Insurance Program, are not likely to intervene, especially in the largest Republican stalwart state of Texas, or for Louisiana. Other states, that have responsible development policies and enforcement, but are also Sanctuary states, will instead be punished for the Sanctuary part.

Update:  just a few weeks ago, Trump dropped the Obama regulations that new structures in flood zones be built two feet higher than previously.  Now Trump is said to be reconsidering that.  A TV interviewee also said that they were still using old flood maps and needed to do a new survey.  A lot of the new housing regulations come through HUD.  Whereas George W. Bush had a horse show producer heading FEMA, President Trump now has Dr. Ben Carson heading HUD.  While Dr. Carson is a distinguished brain surgeon and Trump supporter, he has no experience with housing.

As more wetlands are covered over, the areas covered by one in a hundred, one in five hundred, etc. year flood zones should be increased each year, until something changes in countering floods. Even residents of one-in-a-hundred year zones that must buy insurance, do not. Only 15% of homes in Harris County – Houston have flood insurance, out of 1.6 million housing units. The newest estimate I have seen is 100,000 housing units have been damaged, with likely $30 billion in costs to replace, and the storm costing $80 billion, including lost business.

Now for probabilities. The odds in a given three years of two 1/100 and one 1/1000 year events is one in ten million, times 3 places for the 1/1000 to sit in a three year lineup. That is one out of three million. That is similar to the odds of going up to a roulette wheel and winning four single number bets in a row, plus a win on red also as a fifth bet. Something is fixed here, and the homeowners need to figure out what it is. As President Trump would say, the system is “rigged”.

Postscript:  It occured to me that I should compare this to what in particle physics is a 5-sigma event, or one that occurs five standard deviations away from the center of a bell curve.  By an unnerving coincidence, the 5-sigma event has a probability of 1 in 3.5 million.   In particle physics, this set of flood rarities would qualify as evidence of a new discovery.

You cannot get around this by saying that there are many areas that could have seen a 1/500 year flood. The 1/500 year flood contours are for Houston itself, and have meaning for Houston itself. You cannot get around this by saying that the rare three year streak could have come in any one of three million years. Every time you step up to the roulette wheel you are waging part of your life’s earnings. What happens in this yearly wager counts for now.

If you are planning to raise a family and retire in a house, you expect to pay off your 30 year mortgage, and stay there say 50 years. Not knowing what true odds-flood-zone you are in is the most important fact about your residence. Is buying flood insurance a necessity? Is climate change going to affect frequency and strength of hurricanes, even though current research is not conclusive? Are lingering and then creeping-up-the-entire-coast hurricanes going to be more probable?

The best way to find out the answers is not to cut a third of climate research throughout the government, in one year, without even knowing if that will be made harsher the next year. The best way to prepare is not to cut FEMA’s budget by almost a billion dollars, and cut flood studies and mitigation wherever in the budget that they occur. Trump could not have proposed a budget to leave the nation more unprepared for natural disasters if he had tried (which he did, twice, in 2017, and 2018).

March, before we all have to swim for it!

About Dennis SILVERMAN

I am a retired Professor of Physics and Astronomy at U C Irvine. For two decades I have been active in learning about energy and the environment, and in reporting on those topics for a decade. For the last four years I have added science policy. Lately, I have been reporting on the Covid-19 pandemic of our times.
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