Maritime Continent Deforestation-Induced Extreme Rainfall Regime Shifts During the Early Summer Monsoon Season

The impacts of deforestation over the Maritime Continent (MC) have increasingly raised concerns due to its potential influence on extreme rainfall during the early summer monsoon. This study investigates how MC deforestation modifies extreme rainfall characteristics and associated large-scale circulation responses during May–June (MJ) using 100-year simulations from the Community Earth System Model (CESM1). A control simulation is compared with a deforestation experiment in which MC forests are replaced by grassland, and rainfall changes are quantified using indices defined by the Expert Team on Climate Change Detection and Indices (ETCCDI). Results show that deforestation substantially enhances extreme rainfall over the MC and induces a pronounced rainfall regime shift from weakened light rainfall toward strengthened heavy rainfall, driven by increased atmospheric instability and intensified deep convection. In contrast, rainfall over South China-Taiwan (SCTW) decreases significantly, with both light and extreme rainfall being suppressed. Mechanism analyses indicate that enhanced MC convection induces a meridional circulation response, characterized by anomalous ascent over the tropics and subsidence over SCTW. This subsidence causes tropospheric stabilization, reduced cloud cover, and weakened southwesterly monsoon moisture transport, creating unfavorable conditions for rainfall development over SCTW. Overall, MC deforestation drives a coherent redistribution of early summer monsoon rainfall, featuring an extreme rainfall-dominated regime shift over the MC and circulation-induced rainfall suppression over subtropical East Asia, highlighting the role of tropical land-use change in modulating extreme rainfall and monsoon circulation during the early summer monsoon.