Summer Meteorological Drought over Eastern China at Centennial Scale: Multidecadal Variations and Climate Drivers

Although the changes and impacts of droughts over as long as 60 years have been studied, the centennial-scale multidecadal variations of summer drought in eastern China and their influencing factors remain poorly understood. Based on  two centennial-long datasets of standard precipitation evapotranspiration index (SPEI) and the Twentieth Century Reanalysis version 3, this study investigates the multidecadal variations in summer drought frequency (MVSDF) over eastern China and explores its large-scale climate drivers. Empirical orthogonal function (EOF) analysis identified the first three EOF modes of MVSDF (accounting for 84.5% of the variance), which are closely linked to the Pacific Decadal Oscillation (PDO), global warming, and the Atlantic Multidecadal Oscillation (AMO). (1) Over the centennial timescale, during the positive phase of PDO, the Pacific-Japan teleconnection induces an anomalous lower-tropospheric anticyclone that extends from the Yangtze River to North China, while a cyclonic circulation develops over southern China. This dipole pattern significantly elevates the drought frequency from the Yangtze River to North China, whereas it reduces the likelihood of drought occurrences in southern China. (2) Global warming is observed to enhance the summer droughts in eastern Inner Mongolia, where positive pressure anomaly promotes the subsidence and moisture divergence in the lower troposphere, suppressing precipitation and elevating the potential evapotranspiration. In contrast, the Jianghuai region experiences an opposite effect. (3) The positive phase of AMO triggers a barotropic wave train that resembles the British-Baikal Corridor pattern, resulting in an anticyclonic pattern over North China and a cyclonic one over South China, thereby intensifying the drought frequency in North China. Taken together, these findings emphasize that PDO, global warming, and AMO are key drivers of MVSDF over eastern China at the centennial scale. This provides valuable guidance for predicting long-term droughts and formulating climate adaptation strategies.