California Drought, El Niño, Warm Earth (One more time)

When the rain started I was immediately put in mind of the year 1999. I was living in the East at the time, and as I recall there was a drought. Then in September of 1999 Hurricane Floyd settled into North Carolina with rain that exceeded a 500-year event. Then in 2007 there was drought in Georgia, which as I recall was ultimately ended with a whole lot of rain. (Economic Impact of 2007 Drought) These past events lead us to “just in the nick of time” there is a savior. Perhaps that is the thinking here. 

OK – California and El Niño: In the previous blog of this series, I said that I would be preparing for continued drought in California. This first rainstorm provides much needed and valuable water. It is not drought breaking, and recall that the California water system reaches across the western half of the country through the Colorado river basin. It will require rain and snow of great amounts and extending across large spatial domains to provide more than band-aid relief. It will take time to restore that part of the groundwater that can be restored. Worth remembering that earlier in 2014 there was also rain in California, for example, Jeff’s Masters February 14, Pineapple Express Bringing Significant Rains to Drought-Stricken California.



These events are called atmospheric rivers, and local to the western part of the U.S., the Pineapple Express (really a nice article in Wikipedia - you might contribute to them while you are there). There are two points to make. The first point is to notice the narrowness of the stream of water vapor that is carried to the continent. The second point is that during an El Niño, atmospheric rivers are more likely to occur. As the February 2014 event shows, El Niño is not required for an atmospheric-river event. Likewise, El Niño does not assure atmospheric rivers. Drought breaking or even significant drought relief would occur, most likely, through a succession of atmospheric river events , which span the coastline from southern California up through the Northwest. Such a succession of events is observed, preferentially, with El Niño. So my analysis remains the same. If I have small farm near Cloverdale, California, and if I were looking to the skies for water, I would be preparing for continued drought. And very thankful for the water received, and thinking of how to use it best.

Returning to atmospheric rivers being narrow, when the stream of wet air gets to the coast two things happen. One, the air lifts and cools and precipitation happens, often a lot of it. Two, the weather system spreads along the mountains, much like a wave breaking on a beach. Therefore the spatial extent is greater than the narrow river of moisture brought to the continent. Still, however, precipitation is brought to the region in localized and discrete events. One event does not cover it all. There needs to be rain in the inland watersheds, and it is a good thing to be stored as snow in the mountains. Not all of the rain ends up being immediately available for drought relief.

Now turning to the El Niño forecast, first, using the products I have found to be the clearest and most usable (Australian Bureau of Meteorology). The latest Australian forecast is an El Niño Alert. In April-July of 2014 the level was Alert, which was reduced to a Watch in August – October, The level returned to Alert in November. In the December 2, 2014 update “The El Niño–Southern Oscillation (ENSO) Tracker status remains at El Niño ALERT level. Given current observations and model outlooks, the chance El Niño will be declared in the coming months remains at 70%, triple the average likelihood of an event occurring.”

As we have learned in this series, there is sharing of models and data across the centers. The analysis varies, but is in general consistent. The December 4, 2014 synopsis from the U.S. Climate Prediction Center is “There is an approximately 65% chance that El Niño conditions will be present during the Northern Hemisphere winter and last into the Northern Hemisphere spring 2015.” And further, “Similar to last month, most models predict SST anomalies to be at weak El Niño levels during November-January 2014-15 and to continue above the El Niño threshold into early 2015. Assuming that El Niño fully emerges, the forecaster consensus favors a weak event. In summary, there is an approximately 65% chance of El Niño conditions during the Northern Hemisphere winter, which are expected to last into the Northern Hemisphere spring 2015.”

Next, looking at the Australian ENSO Wrap-up from December 2, 2014. “Many climate indicators remain close to El Niño thresholds, with climate model outlooks suggesting further intensification of conditions remains likely. The Bureau’s ENSO Tracker status is currently at ALERT, indicating at least a 70% chance that El Niño will be declared in the coming months. Whether or not an El Niño fully develops, a number of El Niño-like impacts have already emerged.” And further, “If an El Niño is established, models suggest it will be weak, or moderate at most.”

This week’s rainstorm in Southern California might be viewed as an “El Niño-like impact.” With a strengthening of El Niño, it is reasonable to expect more storms, and more relief from the drought. Still, if I had that farm in California, I would be planning for drought and hoping to enjoy some rain.

Returning one more time to my entry from May 29, 2014 , when I wrote, “even a moderate El Niño this year is likely to lead to the hottest year on record.” My rationale for this statement is that we are living in the hottest decade since we have had easily defended direct temperature measurements. We have remained warm, globally, despite relatively cool temperatures in the eastern Pacific. Given the importance of the eastern Pacific to the global picture, even a small break in the cool pattern is likely to lead to globally historic highs. Let’s do a summary, since modern temperature records began in 1880: 

April 2014 the warmest April
May 2014 the warmest May
June 2014 the warmest June
July 2014 not quite the warmest July
August 2014 the warmest August
September 2014 the warmest September
October 2014 the warmest October (graph)

And from the World Meteorological Organization 2014 on course to be one of hottest, possibly hottest, on record - Exceptional heat and flooding in many parts of the world. Of course to make things interesting we’ve had some nice cold weather in the U.S. recently. Commenters: get ready.

A quick summary. If you read the previous blogs and quotes from the forecast and analysis centers, the El Niño forecast has been quite consistent from the beginning, and at this point, it looks like it will be quite a good El Niño forecast.