The Recent Decline and Recovery of Indian Summer Monsoon Rainfall: Relative Roles of External Forcing and Internal Variability

• DOI: 10.1175/jcli-d-19-0833.1
• Publication Date: 2020-03-26T17:22:21Z
• Authors: Xin Huang; Tianjun Zhou; Andrew Turner; Aiguo Dai; Xiaolong Chen; Robin Clark; Jie Jiang; Wenmin Man; James Murphy; John Rostron; Bo Wu; Lixia Zhang; Wenxia Zhang; Liwei Zou
• Keywords: Forcing (mathematics)

Abstract The Indian summer monsoon (ISM) rainfall affects a large population in South Asia. Observations show decline ISM from 1950 to 1999 and recovery 2013. While the has been attributed global warming, aerosol effects, deforestation, negative-to-positive phase transition of interdecadal Pacific oscillation (IPO), cause for remains largely unclear. Through analyses 57-member perturbed-parameter ensemble model simulations, this study shows that externally forced trend is relatively weak overwhelmed by internal variability during both 1950–99 1999–2013. IPO identified as mode helps modulate recent rainfall. induces changes through moisture convergence anomalies associated with an anomalous Walker circulation meridional tropospheric temperature gradients resultant convection zonal advection. reduces what would have upward 0.01 −0.15 mm day −1 decade period, while 2013 increases value 0.42 0.68 positive-to-negative transition. Such significant modulation historical trends confirmed another 100-member simulations using perturbed initial conditions. Our findings highlight interplay between effects external forcing needs be considered climate adaptation mitigation strategies