Drought in late spring of South China in recent decades

Late spring ( 21 April - 20 May) precipitation to the south of the Yangtze River in China along the East Asian front is a salient feature of the global climate. The present analysis reveals that during 1958 - 2000 South China (26 degrees - 31 degrees N, 110 degrees - 122 degrees E) has undergone a significant decrease in late spring precipitation since the late 1970s. The sudden reduction of the precipitation concurs with a notable cooling in the upper troposphere over the central China (30 degrees - 40 degrees N, 95 degrees - 125 degrees E). The upper-level cooling is associated with an anomalous meridional cell with descending motions in the latitudes 26 degrees - 35 degrees N and low-level northerly winds over southeastern China (22 degrees - 30 degrees N, 110 degrees - 125 degrees E), causing deficient rainfall over South China. The late spring cooling in the upper troposphere over the central China is found to strongly link to the North Atlantic Oscillation (NAO) in the preceding winter. During winters with a positive NAO index, the upper-tropospheric cooling occurs first to the north of the Tibetan Plateau in early - middle spring, then propagates southeastward to central China in late spring. It is suggested that the interdecadal change of the winter NAO is the root cause for the late spring drought over South China in recent decades.