Inter-annual variability of global monsoon precipitation in present-day and future warming scenarios based on 33 Coupled Model Intercomparison Project Phase 5 models

Simulations and future projections of year-to-year variation in global monsoon precipitation (GMP), defined as the summer precipitation amount per unit area within the global monsoon domain, are investigated using the 33 models that participated in Phase 5 of the Coupled Model Intercomparison Project (CMIP5). The inter-annual standard deviation of GMP, which presents the amplitude of year-to-year variability in monsoon rainfall, is simulated well by the multi-model ensemble (MME) mean of the 33 models and of the best five (B5) models. The B5 models show superior skills in reproducing the climatological monsoon precipitation and its inter-annual variability. The inter-annual standard deviations of 25-year GMP in the present day (1979-2005) derived from the MME average of the 33 models and of the B5 models are 0.17 and 0.15mm/day per unit area, respectively, both being close to the observation (0.16mm/day per unit area). Consistent with the observed El Nino-Southern Oscillation (ENSO)-GMP relationship, the simulated variability of GMP is negatively correlated with the sea surface temperature in the Nino areas at the inter-annual timescale. Projections by the 33 CMIP5 models under the RCP4.5 scenario indicate that wet and dry monsoon years would occur more intensively in a warmer climate. Around 61% (20 out of the 33) of the models show enhanced inter-annual variability of GMP by the end of the 21st century (2072-2098) compared to the period 1979-2005. The MME of the B5 models suggests that the amplitude of projected GMP variability would increase by similar to 20% from present day to the late 21st century. However, the increasing rate of GMP variability detected by the 33 models' MME is relatively small (similar to 6%), which is even smaller than the inter-model standard deviation, suggesting the amplitude changes in GMP variability feature non-negligible uncertainty among the 33 models. Under global warming, the inter-annual variation of GMP would still be tightly connected with ENSO, although the projected amplitude changes in ENSO variability are noticeably diverse across the 33 CMIP5 models. The enhanced amplitude of inter-annual GMP variability may be attributable to the increase in mean-state moisture associated with global warming. The dynamic effect related to changes in the variability of monsoon circulation is small and less robust among the 33 CMIP5 models.