Like the great majority of Californians, I’ve been watching our recent weather with both interest and concern. Now that spring has officially arrived and yet another California “rainy season” has ended in disappointment, it’s time to take a look at the larger situation in which we find ourselves. What lessons can we draw from the world of nature about our circumstances and our future?
The answers to questions this big are far from simple, so I’m going to dedicate several successive columns to exploring them. Let’s get started.
If you believe our elected leaders and most of the news media, you would believe that the big story during our recent winter was the lack of precipitation. Quite simply, in this view, everything would be OK if the “drought” would end and we could get back to “normal” rainfall in California.
Allow me to disagree. The biggest story this past winter was our extraordinarily warm temperatures.
If you were paying any attention to what goes on outside, you noticed. Not only did we see almost no frost in the San Joaquin Valley during the traditional wintertime, but at the same time temperatures often ran 5-10 and sometime 15 degrees above the statistical averages for long periods.
Amazingly, this was true both during our long periods of fair weather and also during the very occasional windows of storm activity. And the intensity of the warmth should have shocked us all. Significant changes in long-term weather are often measured as a degree or two. This winter, the averages jumped off the charts.
Let’s look at the numbers. According to NOAA, the average California temperature for the months of December through February for the years 1901 through 2000 was 43.6 degrees Fahrenheit. This year the average reached almost 50 degrees!
The implications of this are enormous, but let’s focus on the result that affects us the most.
Here are some more numbers – facts, if you will. Measured precipitation this past winter in most areas ran about 40-50% of the statistical average. At my residence in Three Rivers, where I have kept careful weather records for more than 25 years, I have collected so far this year 46% of the annual average for this site. By the time the weather year ends on June 30th, I will likely have exceeded 50% of average.
Many other sites in the southern Sierra have recorded similar totals, at least in terms of percentage of average. But if that is the case, why are the projected snowpack runoff figures so incredibly low?
You must have seen this data by now, too. It’s been big news. The official numbers for the Kaweah River watershed document roughly 50% of average precipitation but forecast only 26% of average runoff.
Why the difference — why doesn’t our snowpack match our precipitation this year?
The answer – if you’re still with me — is: temperature. The extraordinary warm temperatures this winter have meant two things for the snowpack.
First, the storms we did have were so warm that very little snow fell below about 9,000 feet. Many areas that usually have good winter snow packs – locations like Giant Forest and Grant Grove — saw bare ground much of this winter.
The second factor was that between storms, the warm weather melted much of the snow that did accumulate even at high altitudes. When I look out the window here in Three Rivers, I see an Alta Peak that looks like June did a decade or two ago. Below 9,000 feet, I see mostly bare rock.
It’s time to wrap this up, so here’s the headline you need to know. Our warm temperatures this past winter cut our snow pack runoff by roughly half and turned a dry weather year into a catastrophic runoff year.
So is this an anomaly? Will things return to “normal” soon? Don’t bet on it. Winter temperatures have been rising steadily in California for more than a century, and all the climate models suggest that our middle and long-term future will see sustained average temperatures very much like those we experienced this past winter. The winter of 2014-2015 may well be an introduction to the “new normal” that will define cool-season temperatures in the twenty-first century.
What does this mean for snowpack runoff? The warmer our climate, the less water we will get from the mountains. This year shows us how it’s going to work. In the future it may well take 200% of average precipitation – something we almost never achieve – just to see what used to be “average” spring runoff.
I hope you are reading this as a “tough love” column, for that’s how it’s intended. Next time, we’ll continue this important conversation – focusing not on temperatures but instead on actual precipitation.
© Wm. Tweed