Technical Advisory Bulletin
El Niño
February 2016
Introduction
People the world over are experiencing the peak effects of the strongest El Niño
event since 1997-98. Scientists state that aside from the polar seasons themselves,
El Niño is the most powerful climate force on Earth. El Niño, a weather pattern
characterized by unusually warm ocean temperatures along the equator in the
Pacific Ocean, has important consequences for weather and climate over the
U.S., particularly during winter. During these weather episodes, normal patterns of
tropical precipitation and atmospheric circulation are disrupted, triggering extreme
climate events around the globe.
Who or What is El Niño?
El Niño Southern Oscillation (ENSO) occurs when sea surface temperatures in the
region of the Pacific known as Nino 3.4 (5 N-5 S and 120 - 170 W [see chart below]
are greater than 0.4 degrees C warmer than the long-term average during August,
September and October.
Scientists state that aside from
the polar seasons themselves, El
Niño is the most powerful climate
force on Earth. El Niño, a weather
pattern characterized by unusually
warm ocean temperatures along
the equator in the Pacific Ocean,
has important consequences for
weather and climate over the U.S.,
particularly during winter.
Global Effects
What You Can Do
El Niño can increase tropical cyclone activity in the central
North Pacific near Hawaii and in the South Pacific, while
decreasing tropical cyclone activity in the Atlantic and the
Australian region.
In addition, the following may have a higher propensity during
El Niño:
Earth scientists at the University of California, Irvine have
analyzed wildfire burned area maps and determined that,
during El Niño events, the number and size of fires increase in
tropical forests across Asia and South America.
Crop and livestock production in southern Africa are generally
weakened by El Niño, while the phenomenon also impacts
agricultural sectors in northern Australia, parts of Indonesia
and a wide swath of Central America and Brazil.
What Causes El Niño?
Usually the wind blows strongly from east to west along the
equator in the Pacific. Typically, there is water piled up in the
western part of the Pacific and in the eastern part, deeper
colder water gets pulled up from below to replace the water
piled up in the west.
A positive feedback pattern emerges when winds weaken
(often associated with a Kelvin wave traversing the Pacific
from west to east). Warm water piled up in the western part
of the Pacific slumps back down to the east and less water
upwells from below there. The warmer ocean has the effect
of further weakening the wind. The cycle continues and El
Niño grows until countered by separate wave phenomena.
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Riverine flooding may be worse than in the past; however, it
is important not to assume you will not have flood problems
based on previous experience or flood maps.
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Storm runoff flooding should be evaluated. If the
topography of the terrain around your property could funnel
water onto your property, take steps to control potential
runoff. Concrete barriers or other products can be used to
divert flow away from your property, doorways or basement
areas.
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It may be advisable to be prepared to quickly move material
or equipment out of basements or areas that may flood.
Similarly follow the other important advice in our previously
issued flood bulletins.
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If your facility has sewer backflow preventers/valves, make
sure you know where they are and how they work.
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Verify with the city that any storm or combination sewer
lines have been recently cleaned and are in good condition.
If your facility has private sewer lines, they should be
cleaned and in good condition.
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El Niño rains may not necessarily result in intense
downpours that cause flooding. They may be persistent
rains that gradually soak the ground. If this occurs trees
are more prone to falling or landslides may occur. It may
be appropriate to remove or trim trees that may damage
buildings or injure people if they fall.
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Landslides can result from intense rainfalls or persistent
Regional Impact
The effects of El Niño upon climate in temperate latitudes show
up most clearly during wintertime. El Niño generally increases
the odds toward wetter- and cooler-than-average conditions
across much of the south, and towards drier and warmer
conditions in many of the northern regions. Most El Niño winters
are mild over western Canada and parts of the northern U.S.,
and wet over the southern U.S. from Texas to Florida.
2 TAB El Niño
soaking rains. Determine if any higher terrain may
be subject to landslides. The CDC website contains
information about landslide emergency preparedness.
What About La Niña?
La Niña events typically bring opposite conditions to that of El
Niño. In places like the northeastern U.S. that are accustomed
to cold and snowy winters, La Niña often makes for especially
hard winters. In the rainy Pacific Northwest, La Niña winters
seem to bring even more rain and snow than usual.
La Niña’s effects on the world’s weather are less predictable
than those wrought by El Niño. This is mainly because of the
big differences in the jet stream and the storm track. El Niño
causes the Pacific storm track to become stronger, to drop
farther south than usual, and to straighten out like a necklace
of weather extending more-or-less straight across the ocean.
The La Niña storm track is weaker and loopy and irregular,
more changeable — so the behavior and direction of the
storms it carries are more difficult to accurately forecast.
OUTLOOK
Though difficult to predict, scientists have become adept at
employing such tools as satellites and buoys moored across
the ocean to detect changes in water and wind temperatures.
What is the outlook for El Niño going forward? The most
recent official diagnosis and outlook was issued in January
by the NOAA/Climate Prediction Center ENSO Diagnostic
Discussion; it called for this El Niño to remain strong through
the 2016 winter, then weaken and dissipate to neutral by late
spring or early summer 2016.
See all our Technical Advisory Bulletins. For additional
information contact your Willis Towers Watson risk control
consultant or Client Advocate.
Contact
If you have any questions, please contact your client service
team or feel free to contact me directly.
Tod B. Ossmann, PE, CPCU, ARM-E, CFI/2, AMBCI
Senior Risk Control Consultant, Property
Willis Towers Watson
[email protected]
Contributions by Sam Toren, PE.
Senior Risk Control Consultant, Property
Willis Towers Watson
[email protected]
3 willistowerswatson.com
CONCLUSION
Generally speaking, El Niño brings:
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Cooler and wetter weather to the southern and Gulf
states with flooding and damage possible
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Warmer weather to western Canada and southern
Alaska
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Drier weather to the Pacific Northwest
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Cooler weather to northern Canada
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Wetter weather to southern California with storms,
flooding and landslides possible
These effects are felt most strongly in the winter
after the onset of the event. It is expected that this
year could bring weather heavily affected by El Niño,
which could be anything from floods and droughts to
landslides and other severe winter weather.
The Atlantic hurricane season is typically diminished
during El Niño. During cold events in the eastern
Pacific, the odds are significantly higher that the
U.S. will experience greater impacts because of
a larger number of tropical cyclones and higher
intensities for each storm. El Niño does not mean
no hurricanes, as several El Niño years have seen
large impacts. For the average coastal resident or
community, this information might suggest accelerating
preparedness plans with a pending La Niña event,
but improved preparedness by risk managers makes
sense at any time.
SOURCES
http://www.nasa.gov/press-release/nasa-examines-global-impacts-of-the-2015-el-ni-o
http://www.un.org/apps/news/story.asp?NewsID=52882#.Vnm6K_5gmM8
http://www.oc.nps.edu/webmodules/ENSO/NA_EN.html
http://www.pmel.noaa.gov/tao/elNiño/impacts.html
http://www.cpc.noaa.gov/products/special_summaries/97_4/
http://www.aoml.noaa.gov/hrd/Landsea/lanina/index.html
http://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/?enso_tab=enso-iri_update
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml
http://www.weather.com/storms/winter/news/el-Niño-snow-season-impact
http://earthguide.ucsd.edu/virtualmuseum/climatechange1/11_1.shtml
http://www.dummies.com/how-to/content/el-Niño-and-la-nina-weathers-sibling-rivalry.html
https://www.fema.gov/el-Niño
http://www.preventionweb.net/english/professional/news/v.php?id=47125
http://www.psdoors.com/flood-protection/ez-dam-flood-barriers/
http://www.preventionweb.net/english/professional/news/v.php?id=46715
http://emergency.cdc.gov/disasters/landslides.asp
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