Vulnerable territories, well known hazards

Vulnerable territories, well known hazards

Sep 13th, 2017

Vulnerable territories, well known hazards are the ingredients of events such as Harvey and Irma. High density industrial operations, hazmat, toxic compounds storage facilities are obvious boosters to the magnitude and duration of resulting consequences.

Vulnerable territories, well known hazards

Vulnerable territories, well known hazards are due to a combination of:

  • Malicious climate.
  • Unforgiving flat topography. Houston is reportedly locally sinking by 2.2 inches per year due to pumping of oil, water and other factors.
  • Facilities handling or storing hazardous material.
  • Non resilient power grids.
  • Insufficient land-use control and zoning, allowing development in flood prone areas.
  • No built-in resilience.
An aerial view shows a home destroyed by Hurricane Harvey in Port Aransas, Texas, Aug. 28, 2017. Army National Guard photo by Sgt. 1st Class Malcolm McClendon Source

Vulnerable territories, well known hazards are the ingredients of predictable catastrophes in Houston, and also any hurricane heading towards the US continent through Florida.

With such a flat topography and meandering rivers it is difficult to protect from flooding, create buffers of any significant volume.

One does not need to be a rocket scientist to imagine that a stronger than usual meteorological event can create havoc.

100 years storm design

We read Harvey was unprecedented. Class 5 hurricanes like Irma occurred 10 times in the last 20 years with an array of different casualty rate and damages. Reportedly the design criteria of the city’s of Houston flood system is a 100-year storm. That 100-year storm is apparently a rainfall total of 13 inches in 24 hours. The problem is that such rain events have reportedly occurred more than eight times in the last 27 years. So, please, nobody invoke a Black Swan. Let’s only talk about a clearly predictable event with very poorly assessed multi-dimensional consequences.

At this point we have to stress the usual confusion people make between frequency, probability and return period. By definition a 100-year storm has an average frequency of 1/100 year meaning a yearly probability of ~1% to hit. However, if we look at the facts, we had 8 events in the last 27 years. The frequency is then almost 30% and the return period is 3.5-years. Thus the conclusion is very different:

  • The probability evaluated for 1 event stands at 22% per year.
  • Having two events per year yields 3%.
  • Finally the yearly probability of having no comparable storm is only 74%.

Exeedance probability

The exceedance probability is the probability of an event being greater than or equal to a given value. For example, to exceed the ill-evaluated 100-year storm above.

The probability that the next storm be the worst ever recorded is 1/(8+1)=0.11 or 11%

The value above is impressive and it is not an opinion: it derives from solid mathematics.

One does not even need to invoke climate change when dealing with Vulnerable territories, well known hazards! However experts have been adamant in stressing that climate change generates warmer temperatures in the Gulf of Mexico, thus fueling more powerful hurricanes. Hurricanes create water surges along the coast line and those antagonize river flows, forbidding a normal drainage. During Katrina, the level of the gulf reportedly surged by 28 feet. Coastal surge during Harvey was no news!

Long term consequences

One can wonder how long it will take to clean-up. Where contaminated materials will be stored? It is even licit to wonder if exclusions zones will have to be defined to ensure public safety.

The US government won’t be releasing an exact estimate for a month. However its lead expert says it looks like the final tab will easily pass the $160 billion cost, in combined private sector and government spending, of Hurricane Katrina in 2005. A disaster modeler with Enki Research quantified Harvey’s cost could mount to $30 billion when including power grid, transportation and other elements that support the region’s energy sector. An insurance analyst at Imperial Capital said the final tally might be as high as $100 billion, with less than a third of Harvey’s losses to be insured. Like usual, a great uncertainty is afflicting these first estimates. However, experience has shown that cognitive biases tend to underestimate the tally in the immediate aftermath of a catastrophe.

As per the costs of future protection, we know that New Orleans’ flood control improvement after Katrina reached $14.2 billion. However that reportedly achieved dubious results as recently flooding occurred again when the pumping system failed, overwhelmed by rainfall.

A view on the future and mitigations

Engineers in the US estimate it could cost hundreds of billions of dollars to build a flood protection system for Houston. It would involve land-use restrictions, new flood barriers and measures already implemented, for example, in the Netherlands.

The Dutch system attempts to defend Amsterdam and Rotterdam from a 10,000-year storm event. It is interesting to compare this with the 100-year underestimated Houston event.

Tokyo, Chicago have enormous underground storage for excess water to prevent flooding, contamination. Why not Houston?

As a matter of fact, The Metropolitan Area Outer Underground Discharge Channel (首都圏外郭放水路 Shutoken Gaikaku Hōsuiro), is an underground water infrastructure project in Kasukabe, Saitama, Japan. It is the world’s largest underground flood water diversion facility, geared towards mitigating overflowing of the city’s major waterways and rivers during rain and typhoon seasons. Construction lasted13 years, at a cost, at the time, of US$3 billion. (source http://www.abc.net.au/catalyst/stories/4112766.htm )

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Category: Consequences, Hazard, Risk analysis, Risk management

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