The El Niño Southern Oscillation, more commonly known as ENSO is a periodic climatic pattern that involves changes in sea surface temperature in the central and eastern tropical Pacific Ocean. It typically occurs between three to seven years where the surface water either warms or cools from 1°C to 3°C compared to normal. It has three phases, El Niño, La Niña, and the neutral phase. El Niño is the warming of the ocean surface, wherein the low-level surface winds blowing from east to west or the easterly winds, weaken or start blowing from the opposite direction. La Niña, as opposite to El Niño, is the cooling of the ocean surface where the normal easterly winds become stronger. The neutral phase of the ENSO is neither El Niño nor La Niña where the sea surface temperature (SST) is generally close to average.
In the Philippines, ENSO is the most significant source of annual variability in rainfall. It is said that during El Niño in the Philippines, rainfall decreases by 14 % in Luzon, 21% in Visayas, and 35% in Mindanao. One of the most damaging and strongest El Niño event that happened in the country is the El Niño of 2015-2016. It lasted for one and a half years (18 months) and affected about a third of the country. Over sixteen provinces and sixty-five municipalities were put to state of calamity. This El Niño event damaged a total of 550,000 hectares of agricultural land and affected over 400,000 farmers. In total, this phenomenon caused a total of 327M USD of agricultural losses.
So, what are the causes and effects if El Niño?
Primary Causes of El Niño
In normal conditions, the wind blow from east to west along the equator in the Pacific, which is called the trade winds. This causes the water to rise up in the western side, and the deeper (also cooler) water in the east to rise up to substitute the water pushed to the west. The warm water in the in the west rises and warms the air, causing a circulation between east and west of the Pacific with warm, moist air rising on the west and cool, dry air descending on the east. All these leads to the reinforcement of the easterly winds, and causes self-perpetuating motion in the air in the Pacific. This self-perpetuating motion causes the trade winds to weaken causing less warm water to be pushed to west and less cold water to be pulled in the east.
Effects of El Niño
1. Effect on aquatic species and sea birds
In normal situations, the ocean water carries nutrients that lie beneath the ocean to the top thereby allowing the fish species living in the upper waters to feed on the planktons that rely on these nutrients. Seaweeds also rely on cool and nutrient-rich water for survival and growth. An El Niño lessens the upwelling of cold water and the uplift of nutrients from the bottom of the ocean.
As a result, fish either migrate to other regions or die during an El Niño because they lack adequate food for growth and survival. When fish have migrated or reduced in number, other aquatic creatures namely the sea birds and seals that feed on the fish are also affected. Off the coast of California, the aquatic populations such as fish, seals, sea lions, and sea birds are normally affected and deaths are registered during El Niño events.
2. Drought and dry conditions
As much as El Niño presents differently from one occasion to another, the surest characteristic is that it creates tremendous changes in weather patterns. On occasion, this may result in extreme dry spells and drought. Indonesia, the Philippines, and Australia mostly witness much drier conditions than usual together with droughts, forest fires and poor crop yields.
These conditions are experienced when the winds that fetch rain to these regions become weaker. It is believed that the deadliest global famine in 1876 that contributed to the millions of deaths was due to the effects of El Niño.
3. Flooding and impact on local/commercial fishing
The change in El Niño conditions prevail for many months and with the ocean temperatures evening out, the resultant rainy weather patterns in the oceans bring about heavy floods that last for extended periods. The heavy floods are experienced far beyond the ocean shores in the main land, destroying property and rendering people homeless for months.
Consequently, local and commercial fishing is many times severely affected. In Peru, South America, and Ecuador, heavier rains witnessed sometimes during El Niño events between January and May often bring about flooding and impacts commercial fishing negatively.
4. Occurrence of Hurricanes, Typhoons, and very cold weather
The warm pacific air is tied to some of the occurrences of serious hurricanes, typhoons, and very cold weather in various parts of the world. In South America, thunderstorms and severe tropical cyclones (hurricanes) are frequently associated with the drastic change in the global wind cycle circulation because of the eastward displacement of atmospheric heat.
Besides, during times when hurricanes are fewer, wetter weather and very cold weather is witnessed during winter and autumn. Some meteorological evidence indicates that the very cold weather in Europe is promoted by the El Niño. For instance, the 2009 severe winter in the UK was party linked to the effects of El Niño. In South Korea and Japan, the resultant warm Pacific wind currents are believed to cause the more intense typhoons.
As we can see, not only in the Philippines, ENSO is one of the most important Earth phenomena as it affects global atmospheric circulation which in turn influences temperature and precipitation patterns across the globe.
Source: https://www.weather.gov/mhx/ensowhat
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