So here we go again. The breaking news is that we’ve had a dry winter and crisis lies ahead. Does it all sound familiar?
It ought to, because dry years in Central California actually occur frequently. A few years ago, I ran the numbers and concluded that over the long run roughly 40% of our winters fall into the significantly dry category versus roughly 30% “normal” (statistically average) and another 30% wet.
So we can be disappointed in our meager winter precipitation, but we have no particular reason to be shocked or surprised.
We did have a dry winter. After a good December that saw the snow pile up in the mountains, January, February, and March all disappointed in the storms department.
Comparing April 1st figures, we have now fallen into the bottom 20% of recent years in terms of precipitation to date. In the past quarter century, the winters of 1990, 1994, 1999, and 2007 all came out just about where we are ending the winter of 2013. Together, these years represent the five driest winters out of the past twenty-five.
Put another way, we’re having a typical one-out-of-every-five winter.
Not to say that this is a good thing. As of April 1st, the forecast snowmelt runoff for the Kaweah River was about 40% of the long-term average. If you want the numbers, that means that the best forecast is that the river will produce a spring runoff of about 140,000 acre feet of water versus an average of 290,000.
Last year was relatively dry also, but not as dry as this season. At my rain gauge in Three Rivers, 2012 was about 20% wetter than 2013. It is not uncommon to have runs here of two or three dry years in a row, and long-term climate records document prehistoric dry periods running much longer.
So if this dry winter is not particularly noteworthy, then why are we all so excited? The answer, of course, is that we have somehow convinced ourselves that we can rely upon what we call “normal” rainfall. All that concept really tells us, of course, is the long-term statistical average for a highly variable climate
Can we blame this dry winter on climate change? The answer is that we should not. As I’ve shown, dry years like this regularly occur in our part of California.
But if climate change does not cause any single dry year, we have to note that long-term meteorological models suggest that we are likely heading into an era when we will see more winters like this one. That will make life here more difficult.
Dry years are hard on farmers and cattle ranchers. They increase the summer fire hazard in our mountain forests. They reduce opportunities for water-based recreation like boating and fishing.
About the only good thing I can write about dry winters is that provide a longer hiking season for those of us who love to spend summer in the High Sierra. This year, most high altitude trails should be open by late May.
So that’s the scoop on our dry winter. There’s no reason to be excited unless we insist on living in a fantasy world. Dry winters are predictable part of life here in Central California and we should expect to experience them regularly.
© Wm. Tweed