Changes in Early Summer Precipitation Characteristics Over South China and Taiwan: CESM2-LE and CMIP6 Multi-Model Simulations and Projections

The May and June precipitation (known as early summer precipitation; ESP) is an important water resource for South China and Taiwan (SCTW). This study explores the similarities and differences between the Community Earth System Model Version 2-Large Ensemble (CESM2-LE) and the Coupled Model Intercomparison Project Phase 6 (CMIP6) multi-model ensemble in simulating the characteristics of ESP over SCTW in the present day, and in projecting the related changes at the end of 21st century. For the present-day simulation, our results showed that CESM2-LE and CMIP6 outperformed each other for different examined features. CESM2-LE was slightly better than CMIP6 in capturing the magnitude of ESP over SCTW, while CMIP6 was more capable of representing the interdecadal shifts in the occurrence timing of the ESP maximum. Both the CESM2-LE and CMIP6 projections indicated that ESP will be enhanced and the phase of maximum ESP will be delayed, from peaking around mid-June in the present to late June in the future. These changes can be attributed to an enhanced short-wave trough over southwest China and a late intensification of the southwesterly wind ahead of the short-wave trough, which help transport more moisture from the north of the South China Sea to SCTW, particularly in mid-to-late June. In addition, relative to CMIP6, CESM2-LE showed less uncertainty in the projected increase in ESP and phase delay. This finding highlights that model diversity may play a more important role than internal variability in attributing the uncertainty of projected changes in ESP over SCTW.