Response of Eastern China Summer Rainfall Modes to Increased Carbon Dioxide Concentration

The spatial distribution of summer rainfall anomalies over eastern China are often characterized by meridionally banded structures. The possible change of these structures in response to global warming is of great significance to water resource management, agricultural development planning, and disaster prevention. Previous studies have shown the critical role of climate variability in modulating these rainfall modes, while studies have seldom considered the model’s internal variability when investigating the responses of rainfall modes to increased greenhouse gas concentration. Based on model simulations with different forcing under CMIP5 (the fifth Coupled Model Inter-comparison Project), this paper analyzes the response of the leading modes of eastern China summer rainfall to increased CO₂ concentration considering the model’s internal variability. Results showed that the increased CO₂ concentration did not change the leading modes of eastern China’s summer rainfall. The triple and dipole modes observed during recent decades remained the leading modes in the abrupt quadruple CO₂ concentration experiment (4×CO₂), and 1% per year increased until quadrupled CO₂ concentration experiment (1%CO₂), with the dipole mode playing a more dominant role. However, the frequency, intensity, and trend of these modes changed. Compared to pre-industrial control simulation (piControl), the temporal variability of the triple and dipole modes decreased under 4×CO₂ forcing. The variability of the dipole mode intensified while the triple mode weakened under 1%CO₂ forcing. With the gradual accumulation of CO₂, the occurrence of the positive and negative phases of these modes changed. The phase of the triple mode, which featured drought over the Yangtze River Basin and floods over North and South China, would happen more frequently. So does the “Southern flood and northern drought” phase of the dipole mode. Compared to the piControl simulation, the sea surface temperature and atmospheric circulation anomalies associated with the dipole and triple modes weakened under 4×CO₂ forcing. While under 1%CO₂ forcing, their differences exhibited regional dependence. The triple mode was associated with weakened anomalies over the Indian and western North Pacific Ocean, while the dipole mode was related to strong central and eastern tropical Pacific and North Pacific sea surface temperature anomalies.