A glacier inventory for the western Nyainqentanglha Range and Nam Co Basin, Tibet, and glacier changes 1976–2009

Abstract

The western Nyainqentanglha Mountain Range is located in the south-eastern centre of the Tibetan Plateau. Its north-western slope drains into Lake Nam Co. The area is of special interest for glacio-climatological research as this region is influenced by both the continental climate of Central Asia and the Indian Monsoon system, and it is situated at the transition zone between temperate and subcontinental glaciers. A glacier inventory for the whole mountain range was generated for the year ~2000 using automated remote sensing and GIS techniques based on Landsat ETM+ and SRTM3 DEM data. The change analysis is based on data from Hexagon KH-9 and Landsat MSS (year 1976), Metric Camera (year 1984), and Landsat TM/ETM+ (1991, 2001, 2005, 2009). Manual adjustment was especially necessary for the panchromatic Hexagon data and for debris-covered glaciers. The whole mountain range contains about 960 glaciers covering an area of 795.6 ± 22.3 km² while the ice in the drainage basin of Nam Co covers 198.1 ± 5.6 km². The median elevation of the glaciers is ~5800 m a with the majority terminating around 5600 m. Five glaciers with debris-covered tongues terminate lower than 5200 m. The glacier area decreased between 1976 and 2001 by about 6 ± 3%, which is less than presented in previous studies based on topographic maps from the 1970s and Landsat data from 2000. Glaciers continued to shrink during the period 2001–2009. No advancing glaciers were detected. Detailed length measurements for five glaciers indicate a retreat of the tongues of around 10 m per year (1976–2009) with higher absolute but lower relative values for the larger glaciers

Increased mass over the Tibetan Plateau: From lakes or glaciers?

“…Zone A has 30 lakes with a mean rate of +0.16 m/yr, including Nam Co and Selin Co, two of the largest lakes after Qinghai Lake. The snow cover in the basins of Nam Co and Selin Co is an important contribution fraction of lake level changes besides glaciers melting and precipitation [ Bolch et al ., ; Yao et al ., ; Zhang et al ., ]. All lakes in zones B (8 lakes) and D (3 lakes) show lake level increase.…”

“…However, whether glacier mass is unchanged or decreasing is not discernible from the combination of GRACE data, and lake level/mass changes. Other evidence from satellite observations and field measurements for the ITP supports the premise that glaciers have been retreating in recent decades [ Bolch et al ., ; Kang et al ., ; Yao et al ., , , ]. Therefore, our analysis is consistent with field measurements that glaciers have been retreating.…”

“…They attributed this gain to an increase of glacier mass balance [ Bamber , ; Jacob et al ., ]. Other field‐based evidences for the Inner Tibet Plateau (ITP) (an endorheic basin), however, showed that glaciers have been retreating in recent decades [ Bolch et al ., ; Kang et al ., ; Yao et al ., , , ]. For example, based on field measurements of glaciers in the ITP started in 2005, the mean annual mass balances in three glaciers of ITP between 2005 and 2009 ranged from −549 to −312 mm [ Yao et al ., ].…”

“…For example, based on field measurements of glaciers in the ITP started in 2005, the mean annual mass balances in three glaciers of ITP between 2005 and 2009 ranged from −549 to −312 mm [ Yao et al ., ]. The glacier area and length in the ITP also indicated an overall decrease tendency over the study period [ Bolch et al ., ; Kang et al ., ; Yao et al ., , ]. In this study, our hypothesis is that a significant part of the mass gain has been coming from increased water mass in the lakes rather than from the mass gain of glaciers.…”

Estimating surface temperature changes of lakes in the Tibetan Plateau using MODIS LST data

“…Of the 21 lakes with negative temperature rates, 19 (90%) are glacial lakes. It is likely that accelerated glacier/snow melt contributed more cold water to these lakes [ Bolch et al , ; Yao et al , , ].…”