The Impact of ENSO on rainfall changes in the northern coast of Central Java

Abstract

This study aims to analyze the influence of the El Niño-Southern Oscillation (ENSO) phenomenon on rainfall variability in the northern coastal region of Central Java. This region is vulnerable to hydrometeorological disasters, such as floods and droughts, which have significant social and economic impacts on local communities. The data used includes seasonal rainfall from 22 rain gauge stations over the period of 1994–2023, as well as the ENSO index identified through the Oceanic Niño Index (ONI). The Monte Carlo Bootstrap Resampling method was employed to assess the significance of rainfall anomalies during El Niño, La Niña, and neutral years. The analysis results indicate that El Niño significantly impacts the reduction of rainfall in the JJA (June-July-August) and SON (September-October-November) seasons, with decreases of more than 70% in some areas, especially in Demak and Semarang. In contrast, La Niña significantly increases rainfall, especially in the JJA season, with an increase of more than 50%. During the DJF (December-January-February) and MAM (March-April-May) seasons, the effects of El Niño and La Niña exhibit more varied patterns. In the DJF season, the impact of El Niño on rainfall is relatively weak, although some coastal areas show increased rainfall. Meanwhile, La Niña during this season leads to increased rainfall across most of the region. In the MAM season, the effects of El Niño show both increases and decreases in rainfall, with variations across most of northern coastal region of Central Java, while La Niña shows the opposite pattern, with reduced rainfall in several areas. The distribution patterns of rainfall reveal marked spatial and temporal variations between the two ENSO phases, providing important implications for disaster mitigation policies in the northern coastal region of Central Java.