What Is A 1000 Year Flood?

By Paul Homewood

As is usual, Roger Pielke destroys the latest alarmist meme with solid analysis:


We’ve all heard the terminology. An extreme event happens — a flood or heat wave — and soon after it is characterized as a “1,000-year event” (or it doesn’t have to be 1,000, it could be any number). This week I watched one of the world’s most visible climate scientists, Michael E. Mann, go on national TV and in process show that he had no idea what the concept actually means.

Let’s start by correcting that climate scientist who expressed a popular misconception (about which climate scientists should know better). A 1,000-year flood does not refer to a level of flooding that comes around every 1,000 years.

As the U.S. Geological Survey explains:

The term “1,000-year flood” means that, statistically speaking, a flood of that magnitude (or greater) has a 1 in 1,000 chance of occurring in any given year. In terms of probability, the 1,000-year flood has a 0.1% chance of happening in any given year. 

Similarly, a 2-year flood has a 50% probability of occurring in any year and a 100-year flood has a 1% chance of occurring in any year. If we are instead talking about two six-sided die, then in the same vernacular rolling snake eyes (2 ones) would be called a 36-roll event. No one talks like that in the dice games I play. No wonder people are confused.

Can you roll snake eyes in two successive rolls? Sure you can. It is certainly rare, especially if you are all by yourself — a 1,296-roll event — but it can happen. Now imagine that you have 30 people in all 50 U.S. states each rolling two dice at the same time, how many snake eyes would you expect across those 1,500 rolls? Now imagine that they roll their dice together every day for a year, or that it is 500 people not 30.

Read the full story here.

In laymen’s terms, Roger is merely pointing out that a 1-in 1000 year event is par for the course somewhere or other when there are thousands of places in the world where such events can occur.

Roger finishes by saying:

The concept is widely misunderstood and implies a set of assumptions about the climate system that are not reflective of reality. I know the concept is now widely used in so-called event attribution analyses and press releases, and that just adds to the confusion. It is also built into the policy fabric of U.S. flood policy and is used in the insurance industry.

But if a decorated climate scientist doesn’t even understand the concept, then it probably won’t work in public discourse. Let’s talk about extreme events without invoking the N-year event.

I would go much farther. This fundamentally dishonest use of statistics is actually deliberate and fraudulent. As its perpetrators know full well.



April 18, 2023 at 02:52PM

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