IOD and ENSO impacts on the extreme stream-flows of Citarum river in Indonesia Netrananda Sahu • Swadhin K. Behera • Yosuke Yamashiki • Kaoru Takara • Toshio Yamagata Received: 1 June 2011 / Accepted: 25 July 2011 Ó Springer-Verlag 2011 Abstract Extreme stream-flow events of Citarum River are derived from the daily stream-flows at the Nanjung gauge station. Those events are identified based on their persistently extreme flows for 6 or more days during boreal fall when the seasonal mean stream-flow starts peaking-up from the lowest seasonal flows of June–August. Most of the extreme events of high-streamflows were related to La Nin ˜a conditions of tropical Pacific. A few of them were also associated with the negative phases of IOD and the newly identified El Nin ˜o Modoki. Unlike the cases of extreme high streamflows, extreme low streamflow events are seen to be associated with the positive IODs. Never- theless, it was also found that the low-stream-flow events related to positive IOD events were also associated with El Nin ˜o events except for one independent event of 1977. Because the occurrence season coincides the peak season of IOD, not only the picked extreme events are seen to fall under the IOD seasons but also there exists a statistically significant correlation of 0.51 between the seasonal IOD index and the seasonal streamflows. There also exists a significant lag correlation when IOD of June–August sea- son leads the streamflows of September–November. A significant but lower correlation coefficient (0.39) is also found between the seasonal streamflow and El Nin ˜o for September–November season only. Keywords Indian Ocean Dipole Á ENSO Modoki Á Extreme stream-flow events Á Citarum river Á Climate variability 1 Introduction The Citarum River is the largest river basins in west Java with a catchment area of 12,000 square kilometers. It flows over 269 km of land and accommodates the need of nearly 10 million people (Mashudi 2001). The river is an important source of water for the central part of Java and supplies 80% of the water demands in Jakarta alone. The river also plays a vital role for the economic development and livelihood of the people by supporting agriculture, fisheries, hydroelec- tric power generation, public water supply and industrial establishment of West Java Province and Jakarta City (Fares and Yudianto 2004). However, at present the river is one of the worst polluted rivers of the world because of large dumping of waste from domestic and industrial sources (ADB 2007). The stream flow variations will lar- gely affect the river’s capacity to sustain those damages. Therefore, it is important to understand the extreme events of river stream-flows through adequate scientific analysis. Streamflow of the Citarum River basin is mainly dependent on the seasonal monsoon rainfall from October to May. The warm pool near Indonesia and the associated ascending branch of Walker circulation play crucial roles in determining rainfall variability in the Maritime N. Sahu (&) Á Y. Yamashiki Á K. Takara Disaster Prevention Research Institute, Innovative Disaster Prevention Technology and Policy Research Laboratory, Kyoto University, Gokasho, Uji City, Kyoto 611-0011, Japan e-mail: nsahu@flood.dpri.kyoto-u.ac.jp S. K. Behera Research Institute for Global Change, JAMSTEC, 3173-25 Showamachi, Yokohama, Kanagawa 236-0001, Japan S. K. Behera Á T. Yamagata Application Laboratory, JAMSTEC, Yokohama, Japan T. Yamagata School of Science, University of Tokyo, 3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan 123 Clim Dyn DOI 10.1007/s00382-011-1158-2