Abstract

The Indian Summer Monsoon (ISM) is known to vary on intraseasonal, decadal, centennial and up to millennial time-scales during the past. Whereas shorter-term variability on subseasonal time-scales influences agricultural outcomes due to drought or flood conditions, longer-term dry conditions on centennial scale might e.g., be related to the downfall of the Indus Valley civilization around 4200 years ago.

In a recent study Sinha et al. (2011) hypothesized that abrupt changes in rainfall over India on centennial time-scales during the last Millennium are associated with active and break spells on intraseasonal timescales. This study investigates in how far this hypothesis can be supported by analysing global and regional climate model simulations for the past 6000 years. It is found that decadal to multi-decadal variability of the ISM can be attributed to changes on the intraseasonal time-scale to some extent during the last Millennium. However, longer-term variability is not found to be related to changes on the intraseasonal timescale but rather linked to sea surface temperature conditions over the Indo-Pacific Warm Pool and the northern Arabian Sea.