San Diego has put every city department on an El Niño working group as it braces for a winter that could bring floods, rough surf, or not much rain at all. Assistant Fire Chief Robert Rezende is leading the planning, and he said crews are watching creeks, rivers and lakes from San Ysidro to Sorrento Valley and Lake Hodges.
The reason the city is moving now is simple: scientists say the Pacific has already reached a very strong El Niño. Tyler Rodenbaugh said an El Niño begins when sea surface temperatures rise one-half degree Celsius above normal, and a very strong one is declared at 1.5 degrees above normal. That is the level scientists are seeing now, which is why emergency planning has shifted into gear before the first serious storms arrive.
The risk is not abstract. Dan Cayan said San Diego saw 70 wet days in 1982-83, far above a normal year with 40 to 45 wet days, and that the 1982-83 and 1997-98 El Niño events each produced nearly 20 inches of rain at Lindbergh Field. A typical year brings about 10 inches there. The 2015-16 Godzilla El Niño, though, produced only 8 inches recorded at Lindbergh Field, a reminder that a strong El Niño does not guarantee a soaked winter.
That uncertainty is why the city is planning for more than just rain. Its stormwater systems are aging and its dams are century-old, which leaves little room for error if a large storm system does arrive. Rezende said the city has to keep a close eye on those low-lying and water-adjacent areas because an extreme weather event could stress them quickly.
The pattern matters because El Niño usually tilts the odds toward wetter winters in Southern California, and strong events have also piled up snowpack in the Sierra Nevada. But the link between ocean warming and rainfall has weakened this century, and Alexander Gershunov said the outcome depends on specific atmospheric rivers, the narrow bands of moisture that move water vapor from the tropics and can unleash extreme rainfall. In other words, the ocean may set the stage, but the storms will decide the plot.
For San Diego, that leaves a hard truth: the city can prepare for the range of hazards, but it cannot yet know whether this winter will bring flooding, waves, or a disappointing amount of rain. The real answer will come storm by storm, when the atmospheric rivers finally show up.
