Attribution of uncertainties in predictions of monsoon precipitation using an energy framework

Recent studies on monsoon dynamics have emphasized that monsoon changes are due to local anomalous Net Energy Input (NEI) in the atmospheric column, rather than being associated with land-sea temperature contrasts as in the classical large-scale sea-breeze view of monsoons. In the energy framework, a positive NEI (convergence of energy) must be balanced by a lateral export of moist static energy, which, if achieved by an overturning cell, is associated with moisture import and net precipitation.

This suggests a strong link between monsoonal precipitations and NEI, providing a pathway to understand uncertainties in predictions of past and future monsoon precipitation.

To investigate this, we exploit the CMIP5 and PMIP3 archives (9 models), comparing simulations of Mid-Holocene (~6000 years ago) and future (end of 21^st century, RCP8.5 scenario) climates to pre-industrial (PI) control climate.

Precipitation responses to past and future forcing in monsoon regions exhibit a wide spread which is, as expected, significantly (and positively) correlated with NEI changes. Yet, the latter explain at best 40% of the spread in the precipitation response. In fact, the correlation between NEI and precipitation changes hides a more complex picture.

We show that changes in atmospheric stratification and differences in the control climate contribute to the uncertainties, with varying degrees depending on regions and climates: while the southern hemisphere monsoons are linked to changes in both stratification and NEI, the northern hemisphere monsoons are more strongly associated with stratification changes. Meanwhile, changes in the mid-Holocene are more dominated by NEI changes than in the future climate when stratification changes are larger.