What we need to know about the El Niño cycle

We have heard many times about the onslaught of El Niño. The tumultuous issues on water supply have made it to the headlines, and the ongoing drought that are widely felt across the Philippines has become part of daily conversations. Counting the cost of El Niño’s impact will run into billions of pesos, particularly in the most vulnerable sectors.

We have to establish a greater understanding of these climate extremes; what it can do to our weather, and how it affects us in the coming months. An important factor to consider in all this is the so-called El Niño Southern Oscillation (ENSO).

The United States’ National Oceanic and Atmospheric Administration defines ENSO as “a recurring climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific Ocean.” This has a direct impact on the Earth’s climate, with cycles of searing droughts and destructive floods affecting millions of people around the globe every year. These climate extremes have resulted in calamitous weather-related events, the spread of disease, and disruptions in the global food supply. ENSO has three (3) phases: Neutral Phase, La Niña, and El Niño.

Neutral Phase

Trade winds steadily blow from the tropical Pacific from east to west, gathering warm waters in the Western Pacific. In contrast, water temperature going to the east becomes cooler as trade winds cool the water drawn up below the sea surface. The temperature difference across the tropical Pacific Ocean causes the air to rise north of the northwest Pacific and descend near South America. This creates a huge connected cycle called the ‘’Walker circulation.’’ Neutral episodes are considered the normal phase in half of the ENSO cycles. While this brings normal weather for the Philippines, drought and floods cannot be ruled out in the equation.

La Niña

At this point, trade winds blow in harder, the equivalent of a Neutral phase intensifying and expanding the warm pool of waters of the tropical Pacific across the equatorial regions of the Philippines, Indonesia, Papua New Guinea, and the South Pacific island nations, including north of Australia, and cooling the waters off toward South America. This increases the east to west temperature difference and strengthens the Walker circulation as the trade winds push even harder, otherwise known as the ‘’feedback loop.’’ Its impact on the climate pattern is largely felt at the beginning of the rainy season and well into the dry season of the following year. With the higher rate of convection and evaporation along the northwest Pacific side, more clouds and rain can be expected along the Western Pacific. As for the Philippines, this will translate to higher risk of devastating floods, lower daytime temperatures, and frequent tropical cyclones, many of which are already within the Philippine Area of Responsibility (PAR).

El Niño

El Niño is almost the direct opposite of La Nina, with trade winds weakening or reversing, allowing warmer waters to drift back toward the east. The change in the ocean temperature patterns results in the Walker circulation breaking down, resulting in even weaker trade winds and a higher tendency of more warming in the east. Once this feedback begins, El Niño has set in. With warm water shifting east, evaporation, clouds, and rain follow, shifting away from the equatorial Western Pacific. This will result in below average rainfall for the region, with greater risks of severe drought, higher temperatures, and more heatwaves for northern and eastern Australia.

Although heatwaves are not common in the Philippines, daytime temperatures during the hot-dry season (March to May) will reach its peak-end fromApril through May, ranging from 34-38°C at most, and the apparent temperature perceived by the body, the “heat index,” increases depending on the amount of moisture in the air. Normally, El Niño translates in many stronger typhoons for the Pacific Northwest since these tropical cyclones emanate from the warm tropical Pacific Ocean but are significantly less through the later part of the year.

The  Philippine Atmospheric, Geophysical and Astronomical Services Administration already declared the hot dry season last month and the effects of the ongoing El Niño in the tropical Pacific has become more apparent. More serious water conservation efforts have to be done to cushion the impact on our dwindling water supply levels in various dam facilities around the country, particularly in Luzon. The situation definitely requires the combined support from the public, the government, and non-governmental organizations.

The implications of drought conditions may still be in its infancy stage today, but experts from the agency have raised further concerns in the coming months. It will take a while before water supply levels return to normal, and this won’t be possible until the rainy season sets in by mid-June.

We have to learn to adapt, despite being powerless to these elements before it hits our most vulnerable communities. Stay #WeatherWiser!

Interested about being #WeatherWiser? Contact us at weatherwiser@weatherph.org.

–By Adonis Manzan

Typhoon Specialist, WeatherPhilippines Foundation, Inc.

10 April 2019






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