As El Niño warms the waters of the equatorial Pacific and prepares the Earth, here in Spain a long series of highly complex atmospheric balances flips a coin: the coin that determines how much rain will fall this winter.
In December 1997, with the largest number of children in recent decades, peninsular Spain had a drop of 134 liters per square metre. This is about 63% higher than the average. In December 2015, with another Super Niño hitting the Pacific Ocean, 17 liters dropped. 20% of normal.
The question is… what awaits us this year?
What Copernicus Says (and What It Doesn’t Say) I bring up Copernicus because it has just presented its predictions for winter and, according to its estimates, the trend clearly indicates something: that we are headed for a warmer and wetter season than usual in most of Europe (although the rain signal is weaker in the south). That is, as La Rioja Mateo explained, the drawing looks a lot more like 1997 than 2015.
What Copernicus does is combine nine seasonal models (from the ECMWF to the Japanese agency) and in its Oct. 10 version change a regime: normal or low pressure at the start of winter and high pressure over the Arctic as it progresses. This is what explains your heat and rain forecast; And also that both in Scandinavia and the South things are not so clear.
But what does all this mean? Basically, a seasonal forecast gives the probability that the three-month average will fall into one of three ranges (above, normal, or below) for the reference year. That’s not saying much. Don’t give details. For Spain and Portugal, Copernicus map readings generated by the Word Alerts app give 70% or more warm winters.
That is what we should care about. For the rest, what Copernicus drew in the second half of winter has another name: the negative NAO. During the negative phase of the North Atlantic Oscillation, the jet stream enters from the west, lowers the latitude, and enters the front. They are water (because the front is laden with moisture) and milder temperatures (because the wind comes from the west and southwest).
That was, in part, what happened last winter, actually.
This gives us a good (and unexpected) reference. The third wettest winter of the century put reservoirs at 84.2% on May 19, and that was great news. But after four and a half months, they were 59.2%: the reservoirs had decreased by about 14,000 hm³.
Most simple: if the thermometer rises, water consumption increases. It is true that everything becomes easier when it rains. But ‘easy’ does not mean ‘problem solving’. And this is something we should have carved in stone at this point.
Picture | Copernicus
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