100 Year Events
By Paul Homewood
h/t John F Hultquist
John sent me the above report by the USGS, concerning floods and droughts in Massachusetts between 1927 and 1988.
The report goes into some detail on certain major floods, but what struck me was the table above, which listed the recurrence intervals. Just note how many are ranged up to 100 years or more.
Given that there are 14 floods listed (and this only includes major events), spread over 61 years, this works out as one every 4 years. What we need to bear in mind, of course, is that there are maybe dozens of locations that are vulnerable to such flooding, just in this one state. Whilst the likelihood of a major flood at any single location may be once every fifty years or so, if there are, say, ten potential locations, one of these would flood on average every five years.
Note that on the list above, each flooding event is a separate event, on a separate date.
Remember this when you so often read about claims of “100 Year Events”.