Projections of East Asian summer monsoon change at global warming of 1.5°C and 2°C

Abstract

Much research is needed regarding two long-term warming targets of the 2015 Paris Agreement, i.e., 1.5°C and 2°C above pre-industrial levels, especially from a regional perspective. The East Asian summer monsoon (EASM) intensity and associated precipitation changes under both warming targets are explored in this study. Multimodel ensemble mean projections by 19 CMIP5 models show small increases in EASM intensity and general increases in summer precipitation at 1.5°and 2°C warming, but with large multimodel standard deviations. Thus, a novel multimodel ensemble pattern regression (EPR) method is applied to give more reliable projections based on the concept of “emergent constraints,” which is effective to tighten the range of multimodel diversity and harmonize the changes of different variables over the EASM region. Future changes projected by using the EPR method suggest decreased precipitation over the Meiyu belt and increased precipitation over the high latitudes of East Asia and central China, together with a considerable weakening of EASM intensity. Furthermore, suppressed precipitation would appear over 30°-40°N of East Asia in June and over the Meiyu belt in July, with enhanced precipitation at their north and south sides. These changes in early summer are attributed to a southeastward retreat of western North Pacific high (WNPSH) and a southward shift of East Asian subtropical jet (EASJ), which weaken the moisture transport via southerly wind at low level and alter vertical motions over the EASM region. In August, precipitation would increase over the high latitudes of East Asia with more moisture from the wetter area over the ocean in the east and decrease over Japan with westward extension of WNPSH. These monthly precipitation changes would finally contribute to a tripolar pattern of EASM precipitation change at 1.5°and 2°C warming. Corrected EASM intensity exhibits a slight difference between 1.5°C and 2°C, but a pronounced moisture increase during extra 0.5°C leads to enhanced EASM precipitation over large areas in East Asia at 2°C warming.