The researchers used a method called Empirical Orthogonal Function (EOF) to study rainfall patterns in the Ciujung-Cidurian watershed. They wanted to understand how rainfall varies over time and space, and how factors like mountain topography and ENSO (El Niño Southern Oscillation) affect it. The EOF analysis showed that monsoon systems dominate annual and seasonal rainfall variance, with different patterns related to ENSO events. By using Rotated Empirical Orthogonal Function (REOF), they found that certain observation stations, like Ragas Hilir and Jongjing, had a significant impact on rainfall variability in the area.