Rainfall Trend Analysis in the Upper Citarum River Basin, Indonesia

Changes in rainfall pattern due to climate change have an impact on streamflow. Extreme rainfall has triggered an annual increase in flooding in the Upper Citarum River Basin. The present study, 18 years (1998–2016) of daily rainfall data at sixteen rain gauge stations was used to identify trends of the annual rainfall, annual maximum 24-h precipitation, and number of a rainy day at the Upper Citarum river basin, Indonesia. The non-parametric statistical test by Mann-Kendall (MK) test and the Sen’s slope estimator were applied to assess the trend of data and the magnitude of the slope. According to the MK test (S value) that approximately 75% of all station tend to increase for rainfall data. Meanwhile, related to Z value at a 95% confidence level, the trend of annual rainfall was increasing significantly in Cipeusing and Cipaku/Paseh stations, while Cisondari station shows a decreasing trend. 50% of the selected stations show a significant trend of the maximum daily rainfall, five stations namely Cicalengka, Cileunca, Rancaekek, Cipeusing, and Cipaku/Paseh stations tend to rise, while Cisondari and Lembang Meteo stations were reduced. Furthermore, Cipaku/Paseh station shows a significant upward trend for number of rainy day, in contrast with 15 stations, which indicate no significant trend of data.