Drought/flood spatial patterns in centennial cold and warm periods of the past 2000 years over eastern China

Drought/flood spatial patterns over eastern China under centennial cold and warm regimes were investigated. The 63-site yearly dry/wet grade data set derived from Chinese historical documents was used, together with an up-to-date 2000-year long temperature series reconstructed from synthesis of 28 temperature proxies in China. We defined the index of difference between drought and flood frequency to reconstruct the drought/flood spatial patterns for five cold periods (440-540, 780-920, 1390-1460, 1600-1700, and 1800-1900 CE) and four warm periods (650-750, 1000-1100, 1190-1290, and 1900-2000 CE). The results showed that there are no consistent patterns over eastern China among all cold/warm periods. However, for most warm periods, drought (flood) dominated north (south) of the Yangtze River. The ensemble mean drought/flood spatial patterns for all warm periods illustrated a dipole pattern with drought (south of 25°N)-flood (25°-30°N)-drought (north of 30°N), with the exception of flood in the Loess Plateau. For all cold periods, the ensemble mean drought/flood spatial patterns showed an east to west distribution, with flood east of 115°E and drought dominant west of 115°E, with the exception of flood between approximately110°E and 105°E. These differences in ensemble mean drought/flood patterns suggest that the probability of drought north of the Yangtze River and flood in the valleys of the XiangJiang and GanJiang rivers south of the Yangtze River is higher in warm periods than in cold periods.