Thursday, April 21, 2016

Understanding the El Nino Phenomenon, Cause and Effect

Dr Abe V Rotor
Living with Nature - School on Blog []
Paaralang Bayan sa Himpapawid (People's School-on-Air) with Ms Melly C Tenorio
738 DZRB AM Band, 8 to 9 evening class, Monday to Friday []

The El Nino Phenomenon is quite hard to explain even in scientific circles.

But first, let me clear El Nino, who to us Filipinos is most endeared in our hearts and homes, referring of course to the Child Jesus. The name was coined in Spanish when the descent of warm water along the coast of Peru and Argentina overcomes the ascending cold current causing massive rainfall and flooding. The phenomenon report coincided on Decmber 25.


A timeline of all the El Nino episodes between 1900 and 2016. It is thought that there have been at least 30 El Niño events since 1900, with the 1982-83, 1997–98 and 2014–16 events among the strongest on record. Since 2000, El Niño events have been observed in 2002–03, 2004–05, 2006–07, 2009–10 and 2015–16.
-----------------------------------------------------Major ENSO (El Nino Southern Occilation) events were recorded in the years 1790–93, 1828, 1876–78, 1891, 1925–26, 1972–73, 1982–83, 1997–98, and 2014–16 with the episodes being among of the strongest ever.

El   Niño events are thought to have been occurring for thousands of years.The biblical story of the 10 Plagues of Egypt is believed to be associated with El Nino, and possibly coincided with other natural disasters such as the eruption of Mt Vesuvius. The death of livestock spawned hordes of flies that caused the outbreak of boils, and triggered sudden increase in frog population. This was favored by the abatement of the Nile River's flow, which in turn caused dinoflagellates to bloom (algal bloom) with the characteristic blood-red color which we term today as Red Tide. 

Death of livestock, other animals and wildlife, engraving

There is no consensus on whether climate change will have any influence on the occurrence, strength or duration of El Niño
Typically, this anomaly happens at irregular intervals of two to seven years, and lasts nine months to two years.  The average period length is five years. When this warming occurs for seven to nine months, it is classified as El Niño "conditions"; when its duration is longer, it is classified as an El Niño "episode".

Historically El Niño is traced to inportant events such as the demise of the Moche and other pre-Columbian Peruvian cultures A recent study suggests a strong El-Niño effect between 1789 and 1793 caused poor crop yields in Europe, which in turn helped touch off the French Revolution. The extreme weather produced by El Niño in 1876–77 gave rise to the most deadly famines of the 19th century. The 1876 famine alone in northern China killed up to 13 million people.
There is also a scientific debate on the very existence of this "new" ENSO. Studies dispute the reality of this statistical distinction or its increasing occurrence, or both. But wth increasing data generated by satelite imaging, more accurate meterological and tarcheological evidences. 

As a matter of review, the oceans of the world are interconnected.  Ocean currents mix and distribute warm and cool water, in the tropical and polar regions, respectively. These currents or gyres, together with atmospheric current, moderate climate, and are important in navigation and ecology on a global scale.     

Ocean currents of the world. El Nino Phenomenon originates at the South Pacific Equatorial Current (counterclockwise) on the Southern hemisphere as shown at the left of this map. This is where the "anomaly," a deviation of the normal oscillation (El Nino Southern Oscillation or ENSO) which occurs as a cycle every 3 to 7 years. Note the distance of the Philippines (top right).  But how are we affected by the El Nino Phenomenon? 

But first, let us visualize with the above diagram, the passing of seasons.  The sun is most intense where it directly strikes the earth.  Thus Summer in the northern hemisphere (left) is the hottest season and December (right) the coolest. There are two equinoxes when the rays of the sun strike the earth midway: Spring (beginning in March, top) and Autumn (beginning September, bottom). Temperate countries have pronounced seasons.  The Philippines experiences only two seasons: wet (June to October/November) and dry (December to May). El Nino is most severe in the dry season which we are presently experiencing.
Normal year showing balanced flow of ocean current. 
El Nino year scenario. A massive mass of water 7 degrees hotter than surface water forms a wall deflecting the cold current on both sides. This warm current moves downward along the western coast of South America, arriving by December 25, thus named El Nino.
The warm mass of water becomes so extensive it create a phenomenon of excessive rainfall and flooding in the geographic region of South  Amnerica (white area). On the other side of the globe, it is warm and dry. 
 Here is a meterological satelite graphical presentation showing the effects of El Nino worldwide. Originally El Nino refers only to those experiencing extreme dry and hot conditions, until recently, to differentiate areas experiencing excessive rainfall and flood, the term La Nina was coined. Thus after an El Nino period, and the same area recieves this time extreme wet conditions, scientists call it El Nina. Thus El Nino and La Nina may be occuring in different regions shown on the map. A place may experience alternate phenomena. 
 It is thought that El Niño affected the Inca Empire in modern-day Peru, who sacrificed humans in order to try and prevent the rains.  
Let's not take El Nino for granted. The North Cotabalo farmers' uprising was perecipitated by hunger. It is ironic that farmers themselves led the uprising which resulted to two deaths, several injuries, and imprisonment of more than a hundred which included serior citizen and prgnant women. 

Flooding caused by La Nina

The major 1982–83 El Niño led to an upsurge of interest from the scientific community. The period 1991–1995 was unusual in that El Niños have rarely occurred in such rapid succession. An especially intense El Niño event in 1998 caused an estimated 16% of the world's reef systems to die. The event temporarily warmed air temperature by 1.5 °C, compared to the usual increase of 0.25 °C associated with El Niño events. Since then, mass coral bleaching has become common worldwide, with all regions having suffered "severe bleaching".


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