Philippine Institute for Development Studies Surian sa mga Pag-aaral Pangkaunlaran ng Pilipinas July 2005
Economic Issue of the Day
Volume V Number 1
Understanding the ENSO phenomenon and its implications
A
sk anyone about what he/she thinks El Niño is and the usual answers would be— a severe drought or a long hot summer or a dry spell followed by heavy rains. While all of these are indeed associated with El Niño, they are, however, merely the effects or impacts of this phenomenon. What it really is lies somewhere in the Pacific.
What it basically is… El Niño is a condition that takes place in the Central and Eastern Equatorial Pacific (CEEP) Ocean, when the sea surface temperature (SST) becomes unusually warmer than the normal temperature. This condition can prevail for more than a year, thus adversely affecting the economy in both local and global scale. The sea or ocean surface usually registers a certain normal temperature. Any departure from this normal level is considered an anomaly. If the temperature rises from normal, it is called a positive anomaly. This condition is associated with El Niño. Conversely, if the temperature drops from normal, it is called a negative anomaly and is more popularly related to La Niña. Either way, any change in the temperature, just like in the human body, indicates that something unusual is taking place and something must be done to address its possible consequences.
Feeling the heat Although the physical occurrence of El Niño (and La Niña) takes place in the Pacific, its effects are felt in other parts of the world, similar to a ripple effect in a big pond. This is due to the so-called southern oscillation (SO) which refers to a “see-saw” in atmospheric pressure between the western (represented by Darwin in Australia) and eastern Pacific (represented by the island of Tahiti). These variations in the atmosphere in the Pacific, combined with changes in the SST as discussed earlier, are responsible for bringing about abnormal climatic events. The interaction between sea and atmosphere variations refers to the El Niño Southern Oscillation (ENSO) and potentially influences extreme climate events in the world (El Niño refers to the ocean or sea component of ENSO while the SO refers to the atmospheric component). El Niño and La Niña are basically flip sides (warm and cold phases, respectively) of the ENSO and as such, do not take place simultaneously in one area/region. However, in terms of teleconnection or the links of climate over great distances, if the eastern part of
El Niño Southern Oscillation (ENSO) The El Niño Southern Oscillation (ENSO) is the interaction between sea and atmosphere variations and potentially influences extreme climate events in the world (El Niño refers to the ocean or sea component of ENSO while the SO refers to the atmospheric component).
❋❋❋
Economic Issue of the Day July 2005
Volume V Number 1
The Economic Issue of the Day is one of a series of PIDS efforts to help in enlightening the public and other interested parties on the concepts behind certain economic issues. This dissemination outlet aims to define and explain, in simple and easy-to-understand terms, basic concepts as they relate to current and everyday economicsrelated matters. This Issue was written by the research team of the project on Bridging the gap between seasonal climate forecasts (SCFs) and decisionmakers in agriculture sponsored by the Australian Centre for International Agricultural Research (ACIAR). The views expressed are those of the author(s) and do not necessarily reflect those of PIDS or the project's sponsors.
❋❋❋
ENSO PHENOMENON
the Pacific experiences an unusual ocean warming and low atmospheric pressure (characteristics of the warm phase or El Niño), then the western part of the Pacific will likely experience the opposite effect, characterized by cooler ocean and high atmospheric pressure.
The implications The effects of ENSO on climate variability all over the globe inevitably have impacts on the various ecological and agricultural production systems around the world. In the Philippines, for instance, an ENSO event can trigger extreme climatic effects such as droughts, strong winds, floods and flashfloods, increasing or decreasing temperatures and many more. The impacts on Philippine climate are initially felt three or five months after the development of an ENSO phenomenon in the tropical Pacific. If the ocean-atmosphere interaction or ENSO is stronger than the usual, however, the Philippines may feel the weather abnormalities much earlier. One of the abnormalities brought about by El Niño, the warm phase of ENSO, is a generally drier weather condition, the effect of which is greatly felt during the dry season. From May to September or during the country’s rainy season due to the southwest monsoon, though, rains may still be expected or felt even with an El Niño occurring in the Pacific. Once the southwest monsoon rainy season ends by late September or early October, rains may be much lesser than normal during an El Niño event. This is critical especially for rice farmers in Central Luzon who traditionally prepare for their second cropping season before the end of the year. If there is indeed an El Niño event, this implies, among others, that enough water should have been stored in the water reservoirs so as to provide irrigation for the crop upon the onset of the dry season (January to April) when hardly any or no rain might be expected. Finally, once the El Niño/La Niña signs start to brew, there is nothing that can stop them from occurring. It is nonetheless useful to understand the processes on how they evolve to be able to be better prepared for them. ❋
El Niño El Nino (EN) is Spanish for “The Christ Child,” a name given by Peruvian fishermen to the phenomenon that they usually observed during the period near Christmas time when the water in the Pacific Ocean off the coast of Peru would become unusually warm. Every two to nine years, for unexplained reason, trade winds in the Pacific region, which drive the surface warm waters of the tropics to the west Pacific, weaken. As a result, these warm waters of the western Pacific drift eastward, resulting in the occurrence of El Nino in the eastern part of the Pacific.
Southern oscillation
Philippine Institute for Development Studies
NEDA sa Makati Building, 106 Amorsolo Street Legaspi Village, Makati City Telephone Nos: 8924059 and 8935705 Fax Nos: 8939589 and 8161091 URL: http://www.pids.gov.ph
Southern oscilllation (SO) is an east-west balancing movement of air masses between the eastern Pacific and the Indo-Australian areas. It is measured as the difference between the overlying atmospheric pressures at Darwin (northern Australia) and Tahiti (south-central Pacific). This term was coined by the British scientist named Sir Gilbert Walker during the 1920s when he observed that when the atmospheric pressure rises in the east, the waters of the eastern Pacific are unusually cold, and when the atmospheric pressure drops in the eastern Pacific, the waters in this part of the Pacific are unusually warm. The opposite effects are observed in the western Pacific.