Precipitation reconstructions in the northern and southern Qilian Mountains based on tree rings of Picea crassifolia

Global warming has strongly influenced the hydroclimatic cycle in arid regions. Here, we established the dendrochronology of spruce on the northern and southern slopes of the Qilian Mountains in the Hexi Corridor based on tree-ring width. The correlation response analysis showed that the radial growth of Picea crassifolia in the study area was limited mainly by precipitation from July of the previous year to June of the current year. Therefore, we developed July–June precipitation reconstructions for the northern and southern slopes of the Qilian Mountains, respectively, based on the ensemble model from the simple linear regression and K-nearest neighbor. Our new reconstructions displayed that during the past 257 years, the northern Qilian Mountains experienced 39 and 38 extreme wet and dry years, and 5 wet and 6 dry periods, respectively, and the southern Qilian Mountains experienced 61 and 51 extreme wet and dry years, and 6 wet and 6 dry periods, respectively. Spatial correlation using CRU precipitation and scPDSI grid data revealed that our reconstruction contains the precipitation signal that is representative of an extensive region of north-central China. The precipitation reconstruction includes major cyclicities of 2–5 years in the north and 7 years in the south, and they document drought/famine events in the late nineteenth century and during the 1920s–1930s. Water vapor from the Pacific Ocean is identified as the main factor responsible for high precipitation events in the study area, while low precipitation events were influenced by continental air masses.