Analysis of deficit summer monsoon rainfall over India in CMIP5 simulations

In this study, we examined the performance of 33 CMIP5 models to simulate summer monsoon rainfall over India for the century-long period 1901–2005. If the standardized rainfall anomaly from the long-term mean is less than –1, it is defined as a deficit summer monsoon season; moreover, for comprehensive analysis, we used moderate and severe deficit summer monsoons. Models are in three categories to capture the annual cycle of rainfall: (i) correct phase and amplitude (peak), (ii) phase with lower amplitude, and (iii) both failed. Many models are unable to mimic the link between subseasonal and seasonal rainfall, which is maximum for the July–August (JA) and June through September (JJAS) rainfall. Except for three models which overestimate the mean intensity of seasonal deficit monsoons, 24 models simulate the composite geographical pattern pretty well for moderate deficit monsoons. Twenty-five models are well represented/simulated in the category of extreme deficit monsoons. The MME simulates extremely dry deficit monsoons over India, with the out-of-phase feature of India's easternmost regions effectively captured. As two potential forcings of Indian Summer Monsoon Rainfall (ISMR), we examine El-Niño Southern Oscillation (ENSO) and Eurasian Snow. A large majority of deficit monsoons are attributed to factors other than El-Niño and Eurasian Snow in all four categories of model simulations. Models that can accurately recreate the distinguishing properties of deficit monsoons could be used to project future changes in the frequency, intensity, and spatial distribution of rainfall associated with extreme deficits. Research highlights In CMIP5, 10 models simulate the annual cycle of rainfall across India reasonably well, while 18 models simulate a dry bias. Subseasonal rainfall correlations (JJAS-JJ, JJAS-JA, and JJAS-AS) depict majority of the models simulates correlations of JJ rainfall with seasonal JJAS rainfall against the observed whereas, observations demonstrate JA rainfall is outstandingly related with the seasonal periodic rainfall. With the exception of three models that overestimate the mean intensity of seasonal deficit monsoons, 24 models for moderate deficit monsoons closely resemble the composite spatial pattern. The MME simulates extremely powerful deficit monsoons over India, with the out-of-phase feature of India's easternmost regions effectively captured. For the Indian Territory, CMIP5 models can replicate less-frequent but more-intense deficit monsoons.