Evolution of megadrought and pluvial events in the Qaidam Basin and Hexi Corridor, Northwest China, during the period 455–2100 CE

Abstract Millennium‐long hydroclimate reconstructions in the Qaidam Basin (QB) and Hexi Corridor (HXC) suggest markedly differing moisture change trends between the two regions in the 20th century; however, it remains unclear whether these current moisture states are exceptional in a long‐term context, and how megadrought and pluvial events have evolved in these regions. Here, we used previously published historical hydroclimate reconstructions combined with model‐based future moisture simulations to assess past, current and future hydroclimate anomalies in a long‐term context (i.e., 455–2100 CE), and investigate the evolution of megadrought and pluvial events. Compared with the QB, moisture variability in the HXC was higher and more prone to the occurrence of severe and long‐lasting megadrought and pluvial events. Megadroughts in the QB mainly occurred in the Little Ice Age (1200–1800 CE) accompanied by lower temperatures, whereas in the HXC, megadroughts mostly occurred during the Medieval Climate Anomaly (800–1200 CE) accompanied by higher temperatures. The Significant Zero crossing of derivatives (SiZer) and Time of Emergence (TOE) analyses were used to reveal the initiation of recent humidity changes and the duration above the natural variability threshold. We found that the QB has experienced a significant wetting trend since the middle of the 20th century, with this trend exceeding the range of natural hydroclimate variability in 1975 CE. The HXC became drier from the early 20th century, but has become wetter since the late 20th century; this trend may exceed the natural hydroclimate variability range by 2032 CE. We also found that the duration and severity of megadrought and pluvial events are positively correlated in each region. Given the higher past hydrological variability in the HXC compared with the QB, our study implies that future extreme hydrological events are more likely to occur in the former of these two regions.