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

Abstract

Abstract 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 × 10 8 m 3 /yr) offsets the dropping upstream runoff (upper Nuxia; −6.89 × 10 8 m 3 /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.