Search

Based on historical simulations and projections under two scenarios of the Shared Socioeconomic Pathways (SSP2‐4.5 and SSP5‐8.5) provided by 32 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), we investigate the future precipitation seasonality changes over China by two indices, the dimensionless seasonality index (DSI) and the relative seasonality index (SI), and the associated physical mechanisms by moisture budget diagnosis. The results show that relative to the baseline period 1995–2014, the DSI is enhanced across almost all of China at the end of the 21st century, with stronger magnitudes in southeastern China and the southern Tibetan Plateau and weaker magnitudes in northwestern China, and national‐mean enhancements are 15% (7%–21%) and 23% (15%–29%) for the multimodel median (25th–75th percentile range across models) under the SSP2‐4.5 and SSP5‐8.5 scenarios, respectively. Projected SI changes show large regional differences, with decreases in northern China and increase in southern China, leading to little change for the national mean. The DSI and SI changes are associated with uneven distributions of changes in absolute amounts and relative proportions of precipitation among seasons, respectively. Further analysis reveals that the contributions of different moisture budget terms to precipitation changes vary across seasons, resulting in changes in the seasonal distribution of precipitation and thus the DSI and SI changes. Specifically, the thermodynamic component of vertical moisture advection primarily determines the greater magnitude of increased precipitation in summer than in winter in most of China, resulting in the DSI change. The reduction in residual term dominates the diminished winter precipitation in southern China, leading to more precipitation concentrated in summer for given annual precipitation and thus the intensification in SI, while the opposite holds true in northern China. [ABSTRACT FROM AUTHOR]

The East Asian summer monsoon (EASM) projection has attracted much attention, whereas there are few investigations on the future changes of the EASM northern boundary. The boundary migration would influence the distribution of precipitation and the related vegetation, and its projection is important for policy development of climate change adaptation. In this study, based on the median of 22 selected Coupled Model Intercomparison Project Phase 6 (CMIP6) models, the linear trends of meridional movement of the EASM northern boundary are found to be 0.45−1.39° of latitude during 2015–2099 based on the three precipitation‐based metrics under three shared socioeconomic pathway scenarios. Spatially, the multimetric climatological EASM northern boundary displays a 70–170 km northwestward advance during 2080–2099 compared to 1981–2010. Such an advance also holds true for most individual models, but the migration magnitudes vary with metrics, scenarios and models. The strengthened EASM in association with the intensified land–sea thermal contrast and the enhanced atmospheric water vapour content in response to global warming account for the northwestward advance of the EASM northern boundary, which is related to the increased possibility of the negative phase of the Pacific decadal oscillation in the future. Additionally, the thermodynamic component due to the increased moisture content contributes more than the dynamic term arising from the reinforced EASM circulations to the intensified precipitation and northwestward migration of the EASM northern boundary. The future advance of the EASM northern boundary favours a "northern flood and southern drought" precipitation pattern over eastern China, which would partly mitigate drought conditions in northern arid regions. [ABSTRACT FROM AUTHOR]

In terms of five categories of East Asian summer monsoon (EASM) indices and one classic meridional wind index, we project the EASM intensity change over the 21st century using 27 global climate models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) under the mid‐range combined scenarios of Shared Socioeconomic Pathways and Representative Concentration Pathways (SSP2‐4.5). Results show that future changes in the EASM intensity are index‐ and model‐dependent. Relative to the reference period 1985–2014, the EASM intensity strengthens slightly based on the east–west thermal contrast indices but varies little as a whole based on the southwest monsoon indices over the 21st century, with large discrepancies among the models. However, it tends to weaken over time based on the other three categories of indices, including the north–south thermal contrast indices, the shear vorticity indices, and the South China Sea monsoon indices. In terms of the meridional wind index that directly measures the EASM circulation in the lower troposphere and holds valid under future global warming, the EASM intensity strengthens significantly over the 21st century as a consequence of increases in zonal and meridional land–sea thermal contrasts between the East Asian continent and the adjacent oceans of western North Pacific and South China Sea. There are certain relationships between the trends of the meridional wind index and other EASM indices. The projections are overall consistent between the ensemble means of all available 27 models and the 14 good models as selected according to their abilities to simulate the present EASM climatology, but with different magnitudes. [ABSTRACT FROM AUTHOR]