In this case, the Qilian juniper tells us about the amount of rain that fell in the east during the fourth century a.d.10 According to tree ring data provided by Qilian juniper samples from Qinghai province on the Tibetan Plateau, it seems that between a.d. 350 and 370, eastern Asia suffered a “megadrought”—which remains the worst drought recorded in the last two thousand years.
