| 摘 要： |
The rapid melting of glaciers has led to severe glacial-hydrological hazards in the Himalayas. An extreme example occurred on 7 February 2021, when a catastrophic mass flow descended from the Ronti glacier at Chamoli, Indian Himalaya, causing widespread devastation, with more than 200 people killed or missing, as well as severe damage to four hydropower projects. To disclose what happened to the Ronti glacier over the past several decades, here, we focused on glacier changes in the Dhauliganga catchment in Uttarakhand, India, over the past two decades. Another five glaciers in the catchment were also studied to map the regional detailed glacier changes. Our achievements are summarized as follows. (1) Based on Landsat images, we constructed two glacier inventories for the catchment in 2001 and 2020. We mapped nearly 413 debris-free glaciers in the catchment between 2001 and 2020 and analyzed the glacier area change at basin and altitude levels. (2) Debris-free glacier area decreased from 477.48 +/- 35.23 km(2) in 2001 to 418.52 +/- 36.18 km(2) in 2020, with a reduction of 58.95 km(2) or 12.35% over the past two decades. (3) The geodetic mass balance was -0.27 +/- 0.10 m w.e.a(-1), with a glacier mass change of -0.12 Gt. a(-1) from 2000 to 2013. Based on the surface elevation difference between the Ice, Cloud, and land Elevation Satellite 2 (ICESat-2) footprints (acquired from 2018 to 2021) and the National Aeronautics and Space Administration (NASA) DEM from 2000 to 2021, the average glacier geodetic mass balance was -0.22 +/- 0.005 m w.e.a(-1), and glacier mass change was -0.10 Gt a(-1). (4) Our results were cross verified by available published elevation difference datasets covering multiple temporal periods, where mass balance was by -0.22 +/- 0.002 m w.e.a(-1) from 1975 to 2000 and -0.28 +/- 0.0001 w.e.a(-1) from 2000 to 2020. (5) Glacier 1 and Glacier 2, the two largest glaciers in the catchment, experienced a decreasing melt rate from 2000 to 2020, while Glacier 3, Glacier 4, and Glacier 5 demonstrated an increasing melt rate. However, Glacier 6, also known as the collapsed Ronti glacier, had a negative mass balance of -0.04 m w.e.a(-1) from 2000 to 2005 and turned positive from 2005 onward with 0.06 m w.e.a(-1) from 2005 to 2010, 0.19 m w.e.a(-1) from 2010 to 2015, and 0.32 m w.e.a(-1) from 2015 to 2020. We postulate that the Ronti glacier collapsed solely because of the significant mass accumulation observed between 3700 to 5500 m a.s.l. Our study helps to understand the collapsed glacier's mass changes over the past two decades and highlights the necessity to monitor mass-gaining glaciers from space to forecast the risks of disasters. |
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