The Recent Climatological Rainfall and Meteorological Drought-Prone Zones in Java, Indonesia: A Spatial Approach Using the Percent of Normal Precipitation Index (PNPI) Method

Abstract

Java is the most vulnerable region to hydrometeorological drought disasters in Indonesia. This study aims to identify recent climatological rainfall patterns and analyze meteorological drought-prone zones in Java. Spatial analysis was conducted using the Percent of Normal Precipitation Index (PNPI) based on high-resolution Global Precipitation Measurement (GPM) data for the period 1998–2024. A hybrid M-LSQM method, applied after M-QM, was introduced to improve satellite rainfall estimates. Results consistently enhanced the accuracy of GPM rainfall estimation, bringing it closer to in-situ observations across diverse topographic categories. The average correlation coefficient (r) reached 0.9498, the average RMSE was 22.869 mm/month, and the Mean Bias Error (MBE) was positive at 0.0184 mm/month. Overall GPM performance was represented by NSE (0.919), categorized as very good. Further analysis revealed that the combination of El Niño and positive IOD events contributed to the intensification of extreme drought (PNPI <40%) in Java. Significant monsoon rainfall patterns were identified, with higher precipitation in western Java compared to the east. High-severity drought-prone zones were concentrated in central and eastern Java (108.5°E–113°E) during extreme drought periods. These findings highlight the urgent need for comprehensive planning and mitigation strategies to reduce the serious impacts of drought in Java.