Waiting for rain

The big El Niño years of the past have all brought lots of rain to Southern California. In Santa Barbara the increased rainfall starts early, averaging about twice the long-term average rain for the rain year by the end of December.

Year Sept Oct Nov Dec 1 Sep-31 Dec
1957 0.00 1.41 0.51 4.51 6.43
1965 0.09 0.00 7.86 3.72 11.67
1972 0.00 0.04 5.69 0.73 6.46
1982 2.07 0.63 5.18 3.07 10.95
1997 0.05 0.15 4.30 6.72 11.22
2015 0.10 0.26 0.13 0.38 0.87
0.27 0.69 1.52 3.02 5.50

This year is different. Instead of having twice as much rain as usual we have had a seventh the normal amount. This El Niño is having the opposite effect from all the others before it.

Now there are several possible explanations. We’ve only got 6 “big El Niño” events in the historical record (because the definition of a “big El Niño” depends on ocean temperature monitoring that simply wasn’t technically feasible until the 1950s). Six events is not a good sample. All of them had large rainfall by now, but perhaps that was just chance.

On the other hand this is the biggest (hottest) El Niño ever recorded. Perhaps it is simply too big and has flipped the weather into yet another pattern. There is some evidence for this. All this year, as El Niño was forming there has been an unusual patch of warm ocean water off the Southern California coast. This patch currently has the effect of diverting storm systems from the west, north and away from Southern California. (Several days later the El Niño temperature has dropped and we seem to be getting a big storm…)

If this be true then as El Niño’s temperatures drop the warm patch should fade and we may get late winter rains. By this time of year, in the past, El Niños have been fading, and this year’s started to decline too, but it has more recently warmed up again (another unprecedented occurrence)… So it may be a while yet before we get any rain…

This isn’t just an El Niño year it is also the fifth year of drought

Year Sept Oct Nov Dec 1 Sep-31 Dec
2011 0.00 1.17 2.15 0.47 3.79
2012 0.01 0.03 2.78 3.20 6.02
2013 0.01 0.11 0.92 0.22 1.26
2014 0.01 0.04 0.86 5.37 6.28
2015 0.10 0.26 0.13 0.38 0.87

And disturbingly enough this year is the driest (so far) of the five.

Generally this is the 14th driest year to January, in other words, 90% of the time we have had more rain by now. Of those 13 drier years only one had above average annual rainfall (and not much above average).

So the historical record does not suggest that we’ll have a drought buster in Santa Barbara.

Unless climate change means that the historical record is now meaningless.


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