Characterizing four decades of accelerated glacial mass loss in the West Nyainqentanglha Range of the Tibetan Plateau

Abstract. Glacier retreat is altering the water regime of the Tibetan Plateau (TP) as the region’s climate changes, but there remain substantial gaps in our knowledge of recent glacier loss in this region due to the difficulty of making- direct high-mountain observations and this limits our ability to predict the future of this important water resource. Here, we assessed 44 years of glacier area and volume changes in the major West Nyainqentanglha Range (WNT) that supplies meltwater to the densely populated Lhasa River basin and Nam Co, the second largest endorheic lake on the TP. Between the two periods 1976–2000 and 2000–2020, we found that the glacier areal retreat rate was more than doubled (from -0.54 ± 0.21 % a^-1 to -1.17 ± 0.30 % a^-1) and surface lowering also accelerated ( from -0.26 ± 0.09 m w.e.a^-1 to -0.37 ± 0.15 m w.e.a^-1) with particularly intense melting after 2014. This acceleration is similar in both timing and magnitude to that observed for Himalayas glaciers farther south. Besides, the areal retreat rate and mass loss rate of most glaciers in WNT were not synchronized. To understand the sensitivity of WNT glaciers to climate forcing, we examined the effects of topography, debris-cover, and the presence of proglacial lakes on our observed changes. We found consistently faster areal retreat but slower thinning rates on steeper slopes and an inconsistent relationship with aspect. We concluded that our observed spatial and temporal patterns of glacier change were dominated by observed local variations temperature and precipitation, the melt-reducing role of supraglacial debris, and the increasing influence of ice-marginal lakes on glacier retreat.