Increase in summer monsoon rainfall over the northeast India during El Niño years since 1600

Abstract

El Nino Southern Oscillation (ENSO) affects Indian Summer Monsoon (ISM) at interseasonal to interannual time scales. Given the heterogeneity in rainfall patterns over India, we have revisited the linkages between El Nino and ISM for the period 1600–2016 in this study. Our analysis based on the instrumental, paleo-proxy, model and satellite data sets show significant spatiotemporal variation in the ISM in response to El Nino. We observed strengthening of ISM over the northeast India (NEI) in conjunction with El Nino events. We suggest that the decadal trends in ISM over the NEI and central India (CI) were controlled by the long term variation in strength of El Nino events. We observed spatial variation in isoGSM derived rainfall and its oxygen isotopic composition (δ18O) in response to El Nino events. We further verified our observations from isotope proxy palaeo-records. Two high resolution speleothem (cave deposits) records of reconstructed ISM during 1600–2008 confirmed the inverse relation of rainfall patterns over CI (negative) and NEI (positive) during moderate to strong El Nino periods. These speleothem records infer a long-term pause in the El Nino (or stronger La Nina) like conditions, which were persisted during 1625–1715 and favored the stronger (weaker) rainfall over the CI (NEI). Furthermore, speleothem records showed stronger El Nino events during 1715–1760 causing significant reduction and enhancement in rainfall amount over CI and NEI, respectively.