So what are we to make of this coming winter? Seldom has the question been more compelling or the answer more significant.
After four consecutive dry winters, Central California is profoundly parched. And I’m not just talking about farmers, but also about the natural systems that inhabit our remaining wildlands.
Here in Three Rivers – where I write these columns – the Kaweah River has shrunk to a trickle and dead oaks stand on many hillsides. Toward Visalia, many valley oaks are showing signs of severe drought stress. The Kaweah Oaks Preserve has lost an alarming number of old trees.
So now what? The big news, of course, is that nearly all meteorological signs point toward a strong El Niño weather pattern this winter. But what does that mean?
The phenomenon known as El Niño is a complex set of changes in the water temperatures across larges expanses of the Pacific Ocean. The warmer the water in certain key areas, the “stronger” an El Niño is said to be.
This year’s El Niño is looking very strong, and strong El Niños often – but not always it is important to note – bring heavy precipitation to southern California and adjoining regions. Some of the wettest winters ever recorded in our part of California – rainy seasons like 1982-1983 and 1997-1998 – came during El Niño winters.
So are we headed into a very wet winter? The answer is that it is possible. And is this a good thing? In many ways – yes – but we should be careful what we wish for.
The far eastern Pacific Ocean – the water off our coast – remains incredibly warm when compared to historic levels. Some areas are running 7-10 degrees above long-term averages. This suggests that our storms this winter – assuming that they come – will likely arrive with very high snowlines.
During storms of this type, the snowline in our local mountains can sometimes rise to 10,000 feet or even higher. When that happens, very little of the precipitation that falls in the mountains is retained as snowpack. Instead, most of the water runs off quickly in powerful surges.
Last winter we received about 50% of our average precipitation but ended up with barely 10% of average snowmelt runoff. This alarming discrepancy resulted from ocean warmth. Put simply, last winter was too warm to allow a significant snowpack to endure in the Sierra.
This winter we could see a similar situation. It is possible that we could see intense storms but still end up with a snowpack that is below average. The rest of the storm water will have come down to the valley during the winter – when farmers don’t need it – as flood runoff.
With good planning, however, much of that winter runoff can be captured in ponding basins and allowed to sink into the ground for future use. Some of it could even end up in the Tulare Lake basin west of Corcoran.
What we can’t do with mid-winter storm runoff is store it in Lake Kaweah for use the following summer. In wet winters, it is Lake Kaweah that protects Visalia from flooding, and there is nothing more useless than a flood control reservoir full of water.
Do I have you feeling uncertain? You should be. Winter weather in Central California is always erratic, and El Niño winters tend to exaggerate that variability.
The odds are in favor of substantial rains this winter, but like all things that involve odds, the outcome is uncertain. We may see intense warm rains and flooding. Or, we may have a good snowpack. Or it just may stay dry.
So here we go. All we have to do to prepare is make plans to control floodwaters while we stay alert to the possibility of continued drought. Such is the nature of the place in which we live.
© Wm. Tweed