Greenhouse warming and anthropogenic aerosols synergistically reduce springtime rainfall in low-latitude East Asia.

Low-latitude East Asia, particularly southern China, has experienced a markedly decreasing springtime rainfall in recent years whereas rainfall trends are weak in mid-latitude East Asia. Details of human influences on this contrasting feature remain uncertain. This study provides a quantification of the relative roles of greenhouse warming and aerosols in the observed spring rainfall trends over East Asia using a state-of-the-art numerical model. Greenhouse warming drives more rapid temperature increases over high-latitude East Asia potentially associated with reduced spring snow than the western North Pacific, which induces an anomalous anticyclone over the East China Sea. This circulation change results in a northwestward extension of the western North Pacific subtropical high, reducing rainfall at low latitudes while moderately increasing rainfall at mid-latitudes. In contrast, anthropogenic aerosols reduce rainfall in both low- and mid-latitude East Asia. Hence, the two anthropogenic factors synergistically reduce rainfall at low latitudes, with a stronger contribution of greenhouse warming (~34%) than aerosols (~17%). In mid-latitude East Asia, their contributions are offset, resulting in weak rainfall trends. Further, the anthropogenic influences are found to be relatively larger under drier conditions, suggesting that a more severe drought can occur in low-latitude East Asia under future drought-conducive conditions.