Sack Lunch Seminar (SLS)

Indian monsoon rainfall is vital for a large share of the world's population.
Both reliably projecting India's future precipitation and unraveling abrupt cessations of monsoon rainfall found in paleorecords require improved understanding of its stability properties. We show that in a comprehensive climate model, monsoon failure is possible but very rare under pre-industrial conditions, while under future warming it becomes much more frequent. We identify the fundamental intraseasonal feedbacks that are responsible for monsoon failure in the climate model, relate these to observational data, and build a statistically predictive model for such failure. Thereby we provide a simple dynamical explanation for future changes in the frequency distribution of seasonal mean all-Indian rainfall. Forced only by global mean temperature and the strength of the Pacific Walker circulation in spring, the simple model reproduces the future trend as well as the multi-decadal variability in seasonal monsoon rainfall, as found in the climate model. The approach offers a novel perspective on large-scale monsoon variability as the result of internal instabilities modulated by pre-seasonal ambient climate conditions.