PUTTING OUR “RAINY SEASON” TO BED

Now that May is here, it’s time to admit that the winter  “rainy season” of 2013-2014 is essentially over. We all know it was dry, but it is worth a minute to take a closer look. Within the numbers one can find a few surprises.

 

Because we live in a Mediterranean climate where nearly all of our rainfall comes during the winter months, the California “weather year” runs from July through June.  This allows us to look at our winter as a unitary whole.

 

Back in January and February you no doubt read and heard a good deal about “record-breaking dryness” and “unprecedented drought.”  This did not turn out to be true. Instead, by the time it ended, the winter of 2013-2014 had become just the kind of extremely dry year we see infrequently but regularly in Central California.

 

Such years, as I have written before, form a predictable part of our climate.  The winter now ending, for example, looks very much like with the winters of 1976-1977 and 1958-1959. This past winter, the rain gauge at my home in Three River recorded a sum that fell closely between those two other very dry winters.

 

Looking further back in time, we find other similar years including 1923-1924 and 1933-1934.  The recent winter of 2012-2013 also falls into this category, which is problem for us since it means this year’s dryness compounds that of last year.

 

Another way to compare years is to look at overall river runoff from the Sierra. Because this water is so important to all of us here in Tulare County, runoff has been measured carefully for nearly a century.

 

The average annual total flow of the Kaweah River is roughly 290,000 acre-feet. The median estimate for this year’s flow is that the river will produce about 23% of that total. Interestingly, the winters of 1976-1977 and 1923-1924 also saw 23% flows — so much for our “unprecedented” winter.

 

None of this means, by the way, that we are not genuinely short of water.  We have built a society and an economy that rely upon at least an average supply of water, and everyone suffers when nature periodically puts us on a low-water diet.

 

The natural world does better under these conditions than the human one.  The native biological systems of Central California have been subjected to periodic severe drought for so long that they consist mostly of those organisms that have worked out strategies for survival in dry times.

 

These strategies allow species to survive even while individual plants and animals fall victim to hostile conditions.  I’ve lost some of the big manzanita bushes on the hills around my house, but not all of them are succumbing to the drought. When wetter times return, manzanita will still be with us as a species.

 

And speaking of wetter times, many of you by now will have read forecasts of a return to El Niño conditions this coming winter.  With luck, such a shift might bring us copious winter rainfall, but a bit of caution remains appropriate at this early stage.

 

El Niño patterns vary in strength, and only the strongest come with a high likelihood of intense precipitation in California.  Early indications in the tropical portions Pacific Ocean do indeed offer hope for a strong El Niño, but it’s too soon to be sure.

 

The winter of 1997-1998 witnessed a strong El Niño in California and very heavy rainfall. The month of February 1998, for example, produced more rainfall at my house than the entire winter of 2013-2014.

 

Some forecasters are suggesting that the upcoming winter of 2014-2015 may be similar in intensity to 1997-1998 so, just for fun, I took the total rainfall from that wet winter and added it to the totals for the past three winters. I divided the sum by four, and guess what I got?

 

The resulting figure is very close (within an inch) to long-term average precipitation here in Three Rivers.  What I am saying is that if I add together one moderately dry year, two extremely dry years and then add an El Niño, what I get is “average” — the figure our local weathermen like to call “normal.”

 

The lesson is important: “average” in Central California is built of prolonged periods of drought and occasional floods. That’s just the way it works.

 

© Wm. Tweed