Intricately interweaving the ramifications of global warming with the cyclical phenomenon known as the Pacific Decadal Oscillation (PDO), transcontinental cyclonic surges originating in the proximity of the Equator could intensify in the impending years. While the havoc-wreaking tropical cyclones near the Equator have lately been quiescent, the 2017 Cyclone Okchi, a formidable exception, battered Kerala, Tamil Nadu, and Sri Lanka. A comprehensive analysis, featured in the journal Nature Communications on Monday, posits that the confluence of global warming and PDO, recurring at intervals of 20-30 years, could usher in an era of augmented cyclonic episodes.
During the period of 1981-2010, the count of such Equator-originated cyclones diminished by 43%, relative to 1951-1980, attributable to the PDO dwelling in a ‘warmer’ or affirmative phase. The warming of the Central Equatorial Pacific, an occurrence known as El Nino, often aligns with reduced precipitation in India. Conversely, cooler-than-usual temperatures, known as La Nina, correlate with surplus rainfall. This intricately interlinked El Nino Southern Oscillation (ENSO) phenomenon recurs every two to seven years across the Pacific. Distinct from the annual rhythm of ENSO, the PDO manifests intermittently and primarily encompasses elevated temperatures in the Western Pacific Ocean and comparatively cooler temperatures in the Eastern Pacific. This dynamic unfolds over substantially protracted time scales. Unlike ENSO, the PDO’s ‘positive’ or ‘warmer phase’ becomes discernible only following several years of meticulously gauging oceanic temperatures and their interplay with the atmospheric milieu.
In 2019, the PDO embarked on a cooler, negative trajectory. Should this persist, it could potentially herald a surge in tropical cyclones during the post-monsoon period, originating proximate to the Equator. Dr. R.S. Ajayamohan, a meteorologist at the Abu Dhabi Polytechnic and a contributor to the study, “While cyclones rarely take form near the Equator, warm waters can engender heightened moisture absorption and amplify their ferocity.”
In the current Pacific panorama, El Nino’s embryonic phase is already impacting central and southern India, leading to recorded precipitation shortfalls of 7% and 17%, correspondingly. Notably, M. Rajeevan, a former Secretary in the Earth Sciences Ministry and co-author of the study, elucidated the significance of PDO. He underscored, “The intricacies of PDO remain relatively underexplored. A symbiosis of a positive PDO and ENSO typically yields adverse consequences. However, when aligned with a negative PDO, it augments rainfall in India.”
