Multi-decadal Variation of the Indian Monsoon Rainfall: Implications of ENSO

Scientific consensus exists on the inverse relationship between the El Nino Southern Oscillation (ENSO) and the Indian Monsoon Rainfall. Conversely, recent historical records of 140 years revealed that the relationship between Indian Monsoon and ENSO has broken down (Kumar et al., 1999). Indian Monsoon rainfall variability on decadal time scale was reconstructed by using seawater oxygen isotopes (d18Ow) estimated from oxygen isotopes and Mg/Ca ratios of Globigerinoides ruber from a sediment core in the Bay of Bengal. A comparison of Indian Monsoon rainfall variability on decadal time scale with the number of ENSO events over last 2000 years reveals an inverse relationship between the monsoon rainfall in the Indian Subcontinent and ENSO Events. Furthermore, d18Ow variations reveal increased monsoon rainfall during Roman Warm Period (RWP) and Medieval Warm Period (MWP) and larger monsoon rainfall fluctuations during the Little Ice Age (LIA). Therefore, our study suggests that on decadal time scale ENSO affects the Indian Monsoon Rainfall through the stronger Walker Circulation and associated tropical convection process.