Let’s take ourselves on wings of nostalgia as it were and try to help ourselves forget, perhaps, for a while, our drab wretched lives: Let us return to a subject written about here before the world lost its mind. All 12 longtime readers might recall my
neurotic obsession interest in California weather. My interest was at first piqued by the incessant harping on and doomsday predictions over what, when looked at objectively, was just typical California weather. Namely: precipitation varies a lot from year to year here in the Golden State. Most years, we get less than average rainfall. Some years, we get a lot more than average rainfall. That’s the pattern evident in the data since there has data to look at.
So, a few years in a row of below average rainfall is not a drought. In any decade, you might get 5, 6, 7 years of below average rainfall, sometimes in a row. Such a pattern seems to simply be the way weather works here on the West Coast, at least since the last glacial maximum ended 10,000 years ago. The existence of California’s extensive system of reservoirs and canals testifies that at some point, some Californians understood that this is the pattern – and built a lot of reservoirs in an attempt to even it out a bit. That these reservoirs are sometimes near empty is a feature, not a bug. If they were always full, that would mean that precipitation around the state was always orderly and consistent. If they were always full, we wouldn’t need them.
Similarly, the three major rivers in the L.A. basin have been turned into concrete lined storm channels. 100 years ago, Angelinos got tired of having their city washed away about every decade, and so made sure the water from the occasional epic storm had somewhere to go. Most years, there will be more skateboarders than water in those channels. But once in a while…
Calling ‘average’ ‘normal’, so that mundane variation become, not ‘below average’, but ‘abnormal’ simply adds to the atmosphere of panic.
So: for the last year, we’ve been hearing about how California had sunk into an unprecedented drought since the epic rain year of 2016/2017 when, you may recall, 200%+ of average rainfall and snowpack nearly washed out the Oroville Dam. the state’s largest reservoir. That ended the then current unprecedented ‘drought’. Before that, the 2005/2006 epic rain year ended another unprecedented drought. And so on, back through the decades. As one remarkably sane meteorologist put it. there are only a few storms between drought and plenty in California.
How are we doing this year? Glad you asked. According to my crazy spread sheet*:
The real accuracy here is probably more in the range of 10 percentage points, rather than the displayed 1/100th of a percentage point -but where’s the fun in that? So, despite the faux accuracy above, we’re really more like something between 70 and 80% of the season average as of today.
Any still here and not drifting into a coma may be interested in the overall pattern of rainfall over time in Contra Costa County, which I’ve determined from other datasets:
Again, while it would be easy (I do it all the time) to come up with a bunch of reasons why it’s wrong to do the math this way, and wrong to mix data from different sets, and so on, it’s also reciprocally hard to come up with any reasons the number would be very off – a bunch of different people calculating rainfall over many years and over a fairly contained and consistent area are not likely to get significantly different results.
The rain season here stretches from July through the following June. The seasonal pattern is something like this: On average, about 16% of total rainfall falls from July through November; about 10% falls in April, May, and June. The other 74% falls in December, January, February, and March.
Using the above as a baseline, as of the end of December, we get on average about 35% of our season total rainfall. This year, we’re at over 200% of expected average rainfall to date so far, and about 75% of the average seasonal total – with the bulk of the rainy season still to come. The Sierra snowpack, the melting of which following summer replenishes many reservoirs, is in a similar state: about 150% of average to date, about 50% of seasonal average.
So, we can stop worrying about the drought for now? Well – no. Unfortunately, it’s not uncommon for the rain and snow to just – stop. A near or completely dry month or two or three, even the peak months, happens regularly. It would be a little unusual if, after a very rainy first half of the season, we got a very dry second half – but hardly unprecedented.
Isn’t this all fascinating? No?
The table is set for a nice 200% year, which would shut up the drought doomsayers for a while, at least. Yet, alas, even only 100% isn’t a sure bet at this point. I’ll keep y’all posted.
*The Contra Costa County Flood Control District maintains a set of 32 rain gages spread across the county. These gages are meant to track current rainfall against a set of “critical antecedent conditions” so as to allow predictions of flooding. The tables on the web page are automatically updated every 15 minutes, allowing the
obsessive attentive observer to watch the rainfall spread out across the county in almost real time. These gages are situated at various altitudes and terrain, so that the experts at the CCC Flood Control District can see where the water is piling up and where it will go. I misuse these gages to measure broad rainfall totals, doing a series of logically and mathematically dubious sums and calculations in order to arrive at the magic number you see above – EXACTLY 76.93% of expected seasonal rainfall has, well, fallen so far. Riiiight. Summing up rainfall and averages across a range of gages and then dividing to get percentages – not strictly scientific. I also do averages of averages, which also has its shortcomings. BUT – I tell myself – the situation is such that these iffy methods are probably roughly right. I’m not applying for grant money are trying to whip up some panic here – I just like taking a stab at a broader measure of rainfall.