Mid-latitude westerlies as a driver of glacier variability in monsoonal High Asia

Glaciers in High Asia store large amounts of water and are affected by climate change. Efforts to determine decadal-scale glacier change are therefore increasing, predicated on the concept that glaciers outside the northwest of the mountain system are controlled by the tropical monsoon. Here we show that the mass balance of Zhadang Glacier on the southern Tibetan Plateau, 2001-2011, was driven by mid-latitude climate as well, on the basis of high-altitude measurements and combined atmospheric-glacier modelling. Results reveal that precipitation conditions in May-June largely determine the annual mass-balance, but they are shaped by both the intensity of Indian summer monsoon onset and mid-latitude dynamics. In particular, large-scale westerly waves control the tropospheric flow strength over the Tibetan Plateau remotely. This strength alone explains 73% of interannual mass-balance variability of Zhadang Glacier, and affects May-June precipitation and summer air temperatures in many parts of High Asia's zone of monsoon influence. Thus, mid-latitude climate should be considered as a possible driver of past and future glacier changes in this zone.