Was there a worried phrase heard more often among western U.S. coastal managers in 2015 than “El Niño”? I’d bet not! The strongest El Niño previously recorded occurred in 1997-1998; however, almost every forecast predicted that the 2015 El Niño would be even stronger, and was shaping up to be the strongest since records began in the 1950s. A quick look at some west coast numbers associated with the last major El Niño event in 1997-1998 explains the concern. But first, the science…
The Science: El Niño is characterized by unusually warm ocean temperatures in the Equatorial Pacific and is an oscillation of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe. Storms increase in frequency and intensity, elevating monthly mean winter significant wave heights and water levels.
From mid-November through December 2015, above-average temperatures dominated over the eastern part of the country, while below-average temperatures were observed over the west. During the first half of January, the Pacific jet stream extended eastward and strengthened. For North America these conditions contributed to below-average temperatures over the southern tier of the U.S. while temperatures remained above average across Alaska and most of Canada.
La Niña, sometimes thought of as El Niño’s opposite number, is a cooling of the equatorial Pacific and brings its own level of mayhem to world weather patterns. The National Oceanic and Atmospheric Administration (NOAA) considers El Niño and La Niña “extreme phases of a naturally occurring cycle.”
The Ocean: One very significant consequence of El Niño conditions is the impact to ocean water levels. In southern California recorded tide levels exceeded predicted levels by more than a foot due to elevated ocean water levels. This caused some consternation in the coastal zone early in the season, as flooding of low-lying areas occurred despite moderate predicted tide heights not historically linked with flood events.
The Damage: El Niño storms in 1982-1983 resulted in 14 deaths in California and $265 million in damages. Although a much higher percentage of the shoreline had been armored following the 1982-1983 storms, high rainfall and storm events associated with the 1997-1998 El Niño event caused havoc, washed away roads and railroad tracks, overflowing flood control channels, caused 17 deaths and in excess of $550 million in damages that winter.
Structural damage was incurred along the south central coast by residences, pier pilings, decking, sewer and water lines. Bulkheads and seawalls were damaged by storm waves throughout Ventura and Los Angeles County necessitating emergency placement of riprap.
The Preparation: Understanding the effects of severe storms fueled by El Niño helps coastal managers prepare communities for the expected erosion and flooding associated with this climate cycle. Some proactive procedures are:
Experience has shown that managers who engage in proactive planning and disaster readiness are best positioned to avoid significant El Niño-caused damage. Furthermore, for coastal zone managers this winter could represent a proxy for the “new normal” associated with future sea level rise.
The Outlook: NOAA’s Climate Prediction Center currently indicates that El Niño conditions are presently occurring and are expected to gradually decrease through spring 2016. As of Jan. 20, 2016, NOAA currently places the probability of La Niña occurring in fall 2016 at 40%.
The Drought: California residents are enjoying the recent rains, but are discouraged from abandoning the significant water savings many counties have experienced. To their question, “How will we know when the drought is over?” – according to state water officials, the answer could be “this year.” However, with California entering the fifth year of the worst drought in the state’s history, heavy rains will have to continue almost non-stop through April to fill depleted reservoirs and rivers and send the Sierra snowpack to at least 150 percent of normal for the drought to be officially over. With the snowpack water content estimated to be 107% of normal, the outlook for recovery looks promising.