You’ve probably heard that this is likely to be “an El Niño Year” but what does that actually mean? How could it affect county operations? What should counties be doing now to prepare? Those are difficult questions. 

Meteorologists can tell us for sure that it’s an El Niño year, because they can measure the temperature of the Pacific Ocean currents and make that determination. In fact, one NASA scientist now says that the warm-water pattern in the Pacific right now is “too big to fail.“ But it’s much harder to know exactly how this El Niño pattern will affect California, let alone a specific county. 

The Q&A below is from the National Oceanic and Atmospheric Administration, and the Scripps Institution of Oceanography. They can’t tell you exactly what’s going to happen this winter, but they can tell you to be prepared. And the Q&A may also help answer questions from the public.

Q What is El Niño?
The El Niño is the popular term for an El Niño-Southern Oscillation (ENSO) event. The migration of warm water from the western Pacific to the eastern Pacific, along the coasts of South America, Central America, and California is called the El Niño. Atmospheric pressure increases in the eastern Pacific and atmospheric pressure decreases in the central Pacific is referred to as the Southern Oscillation.

Q Why does El Niño occur?
El Niño results from interaction between the surface layers of the ocean and the overlying atmosphere in the tropical Pacific. It is the internal dynamics of the ocean and atmosphere system that determine the onset of El Niño events. The physical processes are complicated, but they involve unstable air and sea interaction, as well as planetary scale oceanic waves. The system oscillates between warm (El Niño) to neutral (or cold) conditions with a natural periodicity of roughly 3-4 years. 

Q What is the likelihood that we will have an El Niño in California this fall and winter?
Currently, we’re in a developing El Niño, which is strengthening. Forecasts call for it to continue through the later part of fall or early winter before it peaks. The Climate Prediction Center puts out the probability of the conditions being in place based on their forecast models. There’s an approximately 95% chance that El Niño will continue through Northern Hemisphere winter 2015-16, gradually weakening through spring 2016.

Q What have been the effects from past El Niño events?
The 1982 El Niño brought high rainfall and coastal wave surge in California. A low-pressure system settled off the coast, causing a series of cluster storms, which repeatedly battered the coast. There was extensive flooding, landslides, coastal erosion, and damage to structures. The 1977 El Niño event, in contrast, had a lower than average rainfall since a high pressure system settled over southern California and diverted storms to the north.

Q When is El Niño going to hit?
El Niño isn’t a storm that will hit a specific area at a specific time. Instead, the warmer tropical Pacific waters cause changes to the global atmospheric circulation, resulting in a wide range of changes to global weather. Think of how a big construction project across town can change the flow of traffic near your house, with people being re-routed, side roads taking more traffic, and normal exits and on-ramps closed. Different neighborhoods will be affected most at different times of the day. You would feel the effects of the construction project through its changes to normal patterns, but you wouldn’t expect the construction project to hit your house.

Q What is going to happen in my County?
Over North America, the Pacific jet stream (a river of air that flows from west-to-east) often expands eastward and shifts southward during El Niño, which makes precipitation more likely to occur across the southern tier of the United States. The meteorological community agrees that this year could produce rainfall far above or below average; however, the exact amounts are in dispute. Scripps institution of Oceanography has modeled predicted rainfall, based on a number of possible atmospheric conditions, and has forecast situations ranging from drought up to 300% of the average rainfall for southern California. Meteorologists in central California and the San Francisco Bay area predict that these areas, if they have higher than average rainfalls, would likely have 150% to 200% of average. 

Q What can people do in response to these predictions?
Many properties will be safe during “normal” storms, but could be at risk during an extreme event. Due to El Niño we may experience severe storms this winter, and some may be as severe. Local governments and property owners should undertake common sense inspections of their property to identify prudent maintenance activities to minimize potential storm damage. Some parts of California may be battered by intense storms and that some areas will experience flooding or will have storm induced landslide movement. Preparedness is the best course of action. It could include patching or refacing concrete, cleaning out back drains, utilizing sand bags or geotubes to redirect drainage, removal of foliage debris or placing displaced rock back on an existing revetment.

Q Will El Niño end California’s drought?
Unfortunately, it is scientifically difficult to predict the precipitation amounts of even a strong El Niño. California is in its fourth year of a historical drought and we cannot count on El Niño to halt or reverse drought conditions. A historical look at past years with similar El Niño conditions as currently forecasted provide little guidance as to what California might expect this winter. 

Sources: National Oceanic and Atmospheric Administration
Scripps Institution of Oceanography