Future Projections of Indochina Peninsula Summer Rainfall in a Warmer World and Their Intermodel Uncertainty from CMIP5/6 Multimodel Ensembles

Future change in Indochina Peninsula (ICP) summer rainfall under global warming is an important scientific concern owing to its widespread socioeconomic impacts over this climate-sensitive and densely populated region. Based on the historical simulations and the future high-emission scenarios from phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6), this work explores the projected future changes in summer rainfall over the ICP. The multimodel ensemble (MME) mean future projection shows only a weak increase in ICP summer rainfall under global warming. This is a mutually compensating result of the increase in atmospheric moisture (thermodynamic effect) and the weakening in summer monsoon circulation (dynamical effect). Moreover, the future change projections of ICP summer rainfall feature a large intermodel uncertainty in CMIP5 and CMIP6. In particular, we find that the intermodel uncertainties of sea surface temperature (SST) warming over the tropical western Indian Ocean (TWIO) and the tropical western Pacific (TWP) are two major sources of that of the future projections of ICP summer rainfall. On the one hand, in the context of global warming, a stronger TWIO SST warming would provide more water vapor for ICP rainfall directly via the thermodynamic effect. On the other hand, a stronger TWP SST warming could significantly enhance the ICP summer atmospheric circulation/convection, in favor of the regional rainfall. The present results highlight that an improved projection of tropical SST warming is essential for a reliable future projection of ICP summer rainfall changes under global warming. The possible origins of the uncertainty of the projected tropical SST warming are also discussed. Significance Statement The Indochina Peninsula (ICP) summer rainfall change under future global warming is a widespread scientific and socioeconomic topic because of its tremendous effects on regional agriculture, water resource management, disaster mitigation, ecosystems, food security, and human health. Unfortunately, this research identifies a large intermodel uncertainty of the projected changes in ICP summer rainfall under the future high-emission scenarios from phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6). In particular, such an intermodel uncertainty of the future projections of ICP summer rainfall under global warming is attributed to those of the projected sea surface temperature (SST) warming over both the tropical western Indian Ocean (TWIO) and the tropical western Pacific (TWP), which could affect the ICP summer rainfall changes through the thermodynamic and dynamic processes, respectively. The present results provide clues for improving the future change projections of ICP summer rainfall in a global warmer climate, with potentially enormous benefits for the livelihoods of nearly 300 million people over the ICP.