Mid-Piacenzian and future changes in South Asian precipitation under global warming

Abstract

This study examines the response of South Asian precipitation to global warming during the mid-Piacenzian and in the near future, using modeling data. Compared to the preindustrial period, both the mid-Piacenzian simulations from the Pliocene Model Intercomparison Project Phase 2 and the future projections under the Shared Socioeconomic Pathways 5–8.5 consistently indicate a wetter climate over South Asia, characterized by higher annual net precipitation. Concurrently, simulations show strengthened summer southeasterly winds over the Arabian Sea. The simulated climate anomalies under the mid-Piacenzian conditions align with the paleoclimatic evidence derived from geological records. Based on the validity of the simulated results in the past, together with the similarity to the future projections, it can be inferred that South Asia will continue to experience a wetter climate driven by increasing anthropogenic greenhouse gas emissions. Further analysis reveals that the wetter climate is primarily driven by increased net precipitation during summer and autumn. A moisture budget analysis indicates that the summer wetting over the Indian Peninsula and the Bay of Bengal is caused by thermodynamic mechanisms, which can be attributed to higher atmospheric humidity of the Intertropical Convergence Zone. In contrast, the autumn wetting over the same region is driven by dynamic processes, linked to enhanced cross-equator moisture transport under a positive Indian Ocean Dipole mean state. Additionally, the orographic precipitation is enhanced in the Himalayas and the Western Ghats during both summer and autumn. A key difference between the two warming scenarios is that the wetting is stronger under mid-Piacenzian warming, despite greenhouse gas concentrations being significantly higher in the future scenario. This discrepancy is suggested to be related to the offsetting influence of an El Niño-like mean state, which suppresses South Asian precipitation in the future scenario.