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A Note on the "1000-year" Flood And Our Intuition About Outlier Events

Posted by on | September 13, 2017 | Comments Off

Many media outlets were calling the post-Harvey flooding in East Texas a “1000-year” flood.  Forget for a moment on the craziness of saying this is a 1000-year flood when we have at most about 150 years of weather records for the Houston area.  Consider something else — that our intuition about outlier events tends to suck.

Let’s say the flood affected a quarter of Texas.  This is probably an exaggeration, but it will help the following analysis be conservative.   Based on numbers from Wikipedia, Texas has 268,597 square miles of land area and the whole globe has 57.5 million square miles of land area.  This means that a quarter of Texas is about 1/1000 of the land area of the globe.  Even if this were truly a 1000-year storm, we should see such a storm over a similar area of land every single year on average somewhere in the world.  And if you add in other weather events that I have seen described as “thousand year”, including snowfalls, heat waves, cold waves, droughts, etc. then we should be seeing a thousand-year weather event of some sort over a similar area as that affected by Harvey every few months.

 A Note on the "1000 year" Flood And Our Intuition About Outlier Events  A Note on the "1000 year" Flood And Our Intuition About Outlier Events  A Note on the "1000 year" Flood And Our Intuition About Outlier Events

 A Note on the "1000 year" Flood And Our Intuition About Outlier Events

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