Vanishing Glaciers at Southeast Tibetan Plateau Have Not Offset the Declining Runoff at Yarlung Zangbo

The Third Pole experiences accelerated glacier retreating particularly in the eastern-Himalaya, coinciding with a decrease of monsoon-precipitation in the early 21st century. The extent to which the vanishing abundant maritime glaciers buffer the declining precipitation-runoff remains unclear. Here, with a state-of-the-art enthalpy-based distributed cryosphere-hydrology model and first-hand hydrometeorology observations at Motuo (latest accessible Chinese county), we carefully examine the Yarlung Zangbo basin along Himalayas. We find that during 1998-2019, the rising downstream runoff (lower Nuxia; +6.40 × 10⁸ m³/yr) offsets the dropping upstream runoff (upper Nuxia; -6.89 × 10⁸ m³/yr); however, only the marginal contribution from the vanishing eastern-Himalaya and Nyainqêntanglha glaciers. During 1998-2019, dry upstream illustrates limited glacier melt (15.7 mm/yr) with dominated snow melt (78.8 mm/yr); while much larger at humid downstream (144.8 mm/yr for glacier melt and 219.1 mm/yr for snow melt). From 1981 to 2019, we observe glacier-to-snow melt transition in both upstream and downstream due to glacier degradation and growing nonmonsoon-season precipitation.