Calendar year folly

Everyone always wants to know:

How much rain did we have for the year.

This bar chart shows a history of annual rainfall, as measured using the calendar year, from 1970 to present.  Anything under 47 inches is called a drought year and anything over 59 is a flood year of note.  The long term calendar year average is 53 inches.

The problem is the calendar year …

As measured from January to January doesn’t make good hydrologic sense.  There are two reasons for this: (1) South Florida’s water year starts with the onset of the rainy season in May.  (2) A cut off at January includes months from two separate dry seasons, i.e. January through April of the previous dry season and November through December of the one currently under way. Thus, by regional standards, tallying the annual rainfall from May 1st to April 30th is a better way to discern wet and dry years.

Technically, I shouldn’t even post this graph!

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