What is El Niño?

The El Niño-Southern Oscillation (ENSO) describes the large-scale fluctuations in ocean and atmospheric temperatures in the east-central Equatorial Pacific.  La Niña is sometimes referred to as the cold phase of ENSO and El Niño as the warm phase of ENSO.  These deviations from normal surface sea temperatures can have major impacts on ocean processes and global weather and climate.  An El Niño typically occurs every few years and lasts 9-12 months.

What is forecast to occur?

Typical El Niño effects are likely to develop over North America during the upcoming winter season.  Those effects include warmer-than-average temperatures in the western and northern United States and drier-than-average conditions in the Ohio Valley and the Pacific Northwest. While it is likely that California will experience increased rainfall during winter 2016, additional rain is not certain (Los Angeles Times: El Niño 'is here, and it is huge,' as officials race to prep for winter). Strong El Niño conditions, similar to those that we are experiencing now, occurred in 1982-83 and 1997-98 and brought substantially larger-than-normal amounts of rain and flooding to the Bay Area.

What do we know already?

Increased sea surface temperatures along the California coast have caused “thermal expansion,” i.e., the higher temperatures have caused the ocean water to expand.  This thermal expansion has resulted in the level of the Bay rising by about 9-12 inches over its normal level.  You can see the results of this higher Bay in the graphic below that shows tide levels at the San Francisco Presidio Tide Station.  The blue line represents the “expected” tides during a single week in October 2015 without an El Niño. The green line, which is obviously higher than the blue line, represents the “actual” tides that occurred on those days.  It is easy to see that the actual tides were between 6-12 inches higher – at both high tide and low tide – than would be expected absent an El Niño.

So, what can we expect to happen?

While this rising Bay will recede in the spring as sea surface temperatures cool, there are both short-term and long-term ramifications of the Bay’s higher elevation.

  • This fall and winter: Communities all around the Bay, including shoreline communities, must get ready for storm-related flooding.  A substantial rainstorm, combined with a high tide (or a “king” tide, which is even larger than a normal high tide) can easily create short-term flooding conditions.  Some observers call this “nuisance” flooding because the waters will recede after high tide.  Yet, such flooding is hardly a nuisance to those whose property and livelihoods are affected.  NOAA anticipates that the Bay Area will have 75% more days of shallow coastal flooding due to high winter tides alone – and this estimate does not include any storm-related flooding.
  • Long-term: Scientists predict that climate change will cause ongoing permanent ocean warming and that land-based ice will melt, which will result in higher sea levels. And that includes the level of the Bay – which is predicted to be permanently elevated by around 12 inches by around 2050.  So, the elevated Bay that we all see this fall and winter will be the everyday level of the Bay in about 35 years, resulting in shoreline residents and properties at risk on a daily basis if no action is taken.

tides and currents
To create your own water level graph CLICK HERE

What can you do now?

It is important to be prepared this winter!  For information on how residents and businesses can prepare for upcoming storms and floods, go to the California Storm Ready.  Also, public agencies should read the message from California OES Director Ghilarducci reminding staff to review Emergency Operations Plans and Continuity Plans in anticipation of emergency conditions.

And, it is important to start planning for rising sea level now, before flooding becomes an everyday challenge.  There are many local, regional, state, and national efforts underway to understand both the challenges and opportunities that addressing sea level rise offer.  In the Bay Area, BCDC’s “Adapting to Rising Tides” Program is leading the way through innovative and outcome-oriented adaptation planning. To learn more go to: http://www.adaptingtorisingtides.org.

Additional Resources:

To learn more about tides: https://tidesandcurrents.noaa.gov/education.html

Sf tide station