The recent high occurrence of spring atmospheric droughts over central Hengduan Mountains is unprecedented in 669-year tree-ring records

The Hengduan Mountains, located near the transition zone of the Qinghai-Tibet Plateau and the Yunnan-Guizhou Plateau, experience complex hydro-climate fluctuations, with spring moisture availability having a significant influence on agriculture and ecosystems. To investigate the history of spring moisture and its influencing factors, we developed a tree ring width chronology from 1349 to 2017 in the central Hengduan Mountains. Based on this chronology, we reconstructed the variations of average relative humidity for April to May (RH45 record). Our reconstruction explains 42% (N = 61, R2adj = 0.41, F = 42.22) of the instrumental observations during the calibration period (1953–2017). The reconstructed RH45 record has significant positive correlations with neighbouring drought records, affirming its reliability as a proxy for regional spring moisture. As shown by the reconstructed RH45 record, the 16th to 17th centuries and contemporary decades exhibited the highest frequency of extreme spring hydroclimates. Since 1830, the recurrence time of spring atmospheric droughts is unprecedentedly short during the past six centuries. Additionally, the global warming caused by anthropogenic greenhouse gases has gradually become one of the main factors affecting spring moisture variations of the study area, which may be the main cause of the recent high occurrence of spring atmospheric droughts. Furthermore, we attribute recorded spring atmospheric droughts to the combination of strengthened evaporation induced by high temperatures and weakened moisture transportation induced by weak Indian Summer Monsoon (ISM) circulation, with pluvial springs being results of reversal conditions. Thus, the increasing trend of temperature and the weakening trend of ISM circulation indicate that the high frequency of spring atmospheric droughts is likely to continue in the near future.