Extreme drought events in the years 1877–1878, and 1928, in the southeast Qilian Mountains and the air–sea coupling system

Droughts events have long-lasting effects on economic and social activities, particularly in the semi-arid region of northern China. In this study, four tree ring-width chronologies were developed based on lived Qilian Juniper (Sabina przewalskii Kom.) trees in the southeast Qilian Mountains, China. The four chronologies were developed from 164 cores (82 trees) for the northern marginal of the Asian summer monsoon in China. Tree growth of this area is sensitive to moisture variability of the growth season. During the last 260 years, there had been extreme growth depressions in the years 1877–1878 and 1928, indicating large-scale droughts had occurred in the study area. These extreme drought events had a devastating effect not only on hydrology and agriculture, but also on society and economics. Extreme droughts in 1877–1878 and in 1928 occurring in the study region and most of China were triggered by different climate regimes. The former drought distribution pattern was probably attributable to El Niño events, while the latter was associated with warm and cold air masses.