ANALYSIS OF ENSO OCCURRENCE TRENDS AND INTENSITY VARIABILITY DURING 1960-2019

Abstract

This study evaluates the variability and frequency of ENSO during 1960–2019 using the Oceanic Niño Index (ONI), analyzed across three 20-year cycles with the Mann–Kendall test and Sen’s slope estimator. Results show that El Niño has intensified, reaching a maximum ONI of 2.6°C in 2016, while La Niña has weakened, with a minimum ONI of −1.6°C (2007, 2010). In terms of frequency, the two ENSO phases occurred alternately but differed in number of events and duration across periods. Statistical tests indicate a slight increasing trend for El Niño and a slight decreasing trend for La Niña, though neither reached statistical significance. These findings suggest that ENSO variability during the study period is mainly cyclical and natural, without evidence of a clear long-term trend. The results provide a scientific basis for early forecasting of extreme climatic events and support strategies for climate change adaptation and resource management.