Assessment of the El Niño impact on meteorological drought disaster at Bajulmati watershed – Indonesia

ABSTRACT

A flowchart consists of six main points: 1) The 12 El Niño events occurring between 1981 and 2024, with intensities ranging from weak to strong; 2) The time difference between each of the 12 El Niño events (in months); 3) The duration of each of the 12 El Niño events (in months); 4) The relationship between the SPI-6 meteorological drought index in the Bajulmati watershed and El Niño events from 1981 to 2024; 5) Land cover conditions in the Bajulmati watershed in 2024; 6) The water streamflow response of the Bajulmati watershed during weak, moderate, and strong El Niño events.

Climate change can affect the frequency and intensity of El Niño. In general, the El Niño ocean-atmosphere circulation can reduce rainfall, which has the potential to cause drought in the Indonesian Maritime Continent. Despite its recurrence, there is never an identical El Niño event, so the impact of each El Niño event can be different. This study aims to assess the impact of El Niño on meteorological drought and streamflow discharges in the Bajulmati watershed. This analysis compares the standardized precipitation index (SPI) over different intervals with the El Niño Southern Oscillation (ENSO) index and streamflow discharge. The SPI was calculated from rainfall data for 44 years (1981–2024) at a number of rain gauges. The research results indicate that there is a correlation between the SPI and the occurrence of El Niño, where the impact of El Niño does not occur in real time but with a time lag. The correlation between the ENSO index and the SPI during El Niño events is −0.54 (SPI-1 month), −0.64 (SPI-3 months), −0.9 (SPI-6 months), and −0.75 (SPI-12 months). The streamflow in the Bajulmati watershed can be reduced significantly in line with the ENSO index and particularly during strong El Niño periods.