IOD and ENSO impacts on the extreme stream-flows of Citarum river in Indonesia
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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 Niña conditions of tropical Pacific. A few of them were also associated with the negative phases of IOD and the newly identified El Niño Modoki. Unlike the cases of extreme high streamflows, extreme low streamflow events are seen to be associated with the positive IODs. Nevertheless, it was also found that the low-stream-flow events related to positive IOD events were also associated with El Niño 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 season leads the streamflows of September–November. A significant but lower correlation coefficient (0.39) is also found between the seasonal streamflow and El Niño for September–November season only.
KeywordsIndian Ocean Dipole ENSO Modoki Extreme stream-flow events Citarum river Climate variability
We are thankful to Mr. Yudha Mediawan of the Research Centre for Water Resources, Department of Public Works of Indonesia for providing observed stream-flow data of the Nanjung gauge station. Dr. J. V. Ratnam of Research Institute for Global Change (RIGC), JAMSTEC and Dr. Apip of DPRI, Kyoto University, who used to be Research Center for Limnology-Indonesian Institute of Sciences (LIPI), provided helpful suggestions during the study. We are also thankful to two anonymous reviewers for their constructive suggestions.
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