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Natural Hazards

, Volume 42, Issue 2, pp 273–285 | Cite as

On the impacts of ENSO and Indian Ocean dipole events on sub-regional Indian summer monsoon rainfall

  • Karumuri Ashok
  • N. H. Saji
Original paper

Abstract

The relative impacts of the ENSO and Indian Ocean dipole (IOD) events on Indian summer (June–September) monsoon rainfall at sub-regional scales have been examined in this study. GISST datasets from 1958 to 1998, along with Willmott and Matsuura gridded rainfall data, all India summer monsoon rainfall data, and homogeneous and sub-regional Indian rainfall datasets were used. The spatial distribution of partial correlations between the IOD and summer rainfall over India indicates a significant impact on rainfall along the monsoon trough regions, parts of the southwest coastal regions of India, and also over Pakistan, Afghanistan, and Iran. ENSO events have a wider impact, although opposite in nature over the monsoon trough region to that of IOD events. The ENSO (IOD) index is negatively (positively) correlated (significant at the 95% confidence level from a two-tailed Student t-test) with summer monsoon rainfall over seven (four) of the eight homogeneous rainfall zones of India. During summer, ENSO events also cause drought over northern Sri Lanka, whereas the IOD events cause surplus rainfall in its south. On monthly scales, the ENSO and IOD events have significant impacts on many parts of India. In general, the magnitude of ENSO-related correlations is greater than those related to the IOD. The monthly-stratified IOD variability during each of the months from July to September has a significant impact on Indian summer monsoon rainfall variability over different parts of India, confirming that strong IOD events indeed affect the Indian summer monsoon.

Keywords

Indian summer monsoon Indian Ocean dipole ENSO Impacts 

Notes

Acknowledgements

The subdivisional and homogeneous Indian rainfall sets were downloaded from http://www.tropmet.res.in, the IITM website. The figures in this paper were produced using COLA/GrADS software. The authors acknowledge Professor T. Yamagata and Drs S. K. Behera and Anguluri S. Rao for discussions.

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Copyright information

© Springer Science+Business Media, Inc. 2007

Authors and Affiliations

  1. 1.Frontier Research Center for Global Change (FRCGC/JAMSTEC)YokohamaJapan
  2. 2.International Pacific Research CenterUniversity of Hawaii at ManoaHonoluluUSA

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