Sunny with a good chance of water restrictions

Filed in Uncategorized by on January 26, 2009 132 Comments

Well…the rain early in the weekend was beneficial for those who saw it…but consider this: even in the areas that saw significant rainfall, 7-day totals (which includes 5 days of bone dry weather) were STILL below normal. And now we’re entering another extended dry period–perhaps very extended. 00Z GFS is utterly miserable, with no rain at all save for a few spits on day 15. Unfortunately, this jibes with the ECMWF, which gives considerable confidence in calling for a new 9-11 day dry period (and easily 16+ days once again). This will effectively prevent NorCal from escaping extreme drought and all but guarantee routine-changing (not to mention economy shattering) water restrictions throughout the state.

The current situation–especially if the next two weeks really are dry–is becoming rather rapidly more dire. There may be some local basins–ones that are actually dependent on local rainfall and not the Sierra snowpack–that could actually run out of water by next fall. Agriculture in the Central Valley will be severely disrupted, perhaps for years to come, and in some cases more marginal farmland may be permanently abandoned. Water deliveries will certainly be less than 20% of promised, and possibly 0% if things continue in the direction that they are currently headed. As Inyo points out, a large part (if not the majority) of these very serious consequences are a result of the way in which water has been used historically in CA. Though we are now officially experiencing “extreme drought” conditions in NorCal, the last few years (and even this winter) have not been representative of an “extreme drought” in strictly climatological terms. Though we are currently experiencing moderate to severe meteorological drought, it has certainly not been extreme, considering that tree ring studies have shown that some CA dry spells in the past few centuries have lasted decades and produced some years with essentially no rainfall whatsoever. Regardless of the cause, though, we’re going to feel the effects of this one for quite some time.

Why be pessimistic about the rest of the winter? Well, La Nina conditions, against statistical odds, appear to be expanding and cold anomalies strengthening in the East Pacific even more than was envisioned a month or two ago. Considering the atmospheric response to a true La Nina episode, there is a chance that CA precip will essentially shut down for the second half of the “wet season.” This happens with some regularity during moderate or stronger La Nina years. Now, it is also important to keep in mind that some of CA’s biggest floods in the historical record have occurred during La Nina years, and so it would be untrue to say that it is impossible to have above-average rainfall in the late winter. Given antecedent conditions, however, and the extremely dry extended forecast at the moment, I don’t think this is likely. Stay tuned…but for a while…there will be no rainfall on the horizon.