How often do ENSO events occur, and are they always so strong?
On average they occur every 3-6 years but only irregularly and not as predictably as the astronomically controlled tides. As measured by the degree of warming, every other event tends to stronger or weaker, with the strong ones occurring only at 8 to 15 year intervals. The intervening weak and moderate events do not typically bring such disastrous consequences. The events of 1982/83 and 1997/98 were unusually strong, equaled historically only by events in the late 1800s. Really big events like 1982/83 and 1997/98 occur only a few times in a century.
