Multi-scale drought and ocean-atmosphere variability in monsoon Asia

Spatially extensive and persistent drought episodes have repeatedly influenced human history, including the 'Strange Parallels' drought event inmonsoon Asia during the mid-18th century. Here we explore the dynamics of sustained monsoon failure using observed and tree-ring reconstructed drought patterns and a 1300-year pre-industrial community earth system model control run. Both modern observational and climate model drought patterns during years with extremely weakened South Asian monsoon resemble those reconstructed for the Strange Parallels drought. Model analysis reveals that this pattern arises during boreal spring over Southeast Asia, with decreased precipitation and moisture flux, while related summertime climate anomalies are confined tothe Indian subcontinent. Years with simulated South Asian drying exhibit canonicalElNiño conditions over the Pacific and associated shifts in the Walker circulation. In contrast, multi-year drought periods, resembling those sustained during the Strange Parallels drought, feature anomalous Pacific warming around the dateline, typical of ElNiño Modoki events.