Positive covariance between temperature and precipitation affects dendroclimatological reconstructions

Living and relict Qilian juniper (Juniperus przewalskii Kom.) trees from the northeastern Tibetan Plateau offer an exceptional high-resolution paleoclimate archive spanning centuries to millennia. However, the co-occurrence of different climate signals exhibited by the same trees and chronologies may challenge the interpretation, and even reliability, of dendroclimatological reconstructions. Here, we analyse temperature and precipitation measurements from 60 meteorological stations northeast of the Tibetan Plateau between 1139 and 3663 m asl. We find that summer temperature and precipitation are positively correlated at higher elevations, while they tend to reveal inverse relationships at lower elevations. We also show that anthropogenic warming has led to wetter conditions at higher elevations but drier conditions at lower elevations. Our results further suggest that tree ring-based hydroclimate reconstructions from semi-arid Asian mountain systems are localised representations, which are usually not captured by gridded climate data.