Nature: Glaciers are among the best indicators of terrestrial climate variability, contribute importantly to water resources in many mountainous regions1, 2 and are a major contributor to global sea level rise3, 4. In the Hindu Kush–Karakoram–Himalaya region (HKKH), a paucity of appropriate glacier data has prevented a comprehensive assessment of current regional mass balance5. There is, however, indirect evidence of a complex pattern of glacial responses5, 6, 7, 8 in reaction to heterogeneous climate change signals9. Here we use satellite laser altimetry and a global elevation model to show widespread glacier wastage in the eastern, central and south-western parts of the HKKH during 2003–08. Maximal regional thinning rates were 0.66 ± 0.09 metres per year in the Jammu–Kashmir region.
Conversely, in the Karakoram, glaciers thinned only slightly by a few centimetres per year. Contrary to expectations, regionally averaged thinning rates under debris-mantled ice were similar to those of clean ice despite insulation by debris covers. The 2003–08 specific mass balance for our entire HKKH study region was −0.21 ± 0.05 m yr−1 water equivalent, significantly less negative than the estimated global average for glaciers and ice caps4, 10.
This difference is mainly an effect of the balanced glacier mass budget in the Karakoram. The HKKH sea level contribution amounts to one per cent of the present-day sea level rise11. Our 2003–08 mass budget of −12.8 ± 3.5 gigatonnes (Gt) per year is more negative than recent satellite-gravimetry-based estimates of −5 ± 3 Gt yr−1 over 2003–10 (ref. 12). For the mountain catchments of the Indus and Ganges basins13, the glacier imbalance contributed about 3.5% and about 2.0%, respectively, to the annual average river discharge13, and up to 10% for the Upper Indus basin14.
Fig: Data are shown on a 1° grid with overlapping rectangular geographic averaging cells of 2° × 2°. Trends are based on autumn ICESat acquisitions. The mean trends for each subregion are given in metres per year. Only ICESat footprints over glaciers.
Fig: Data are given for the five sub-regions defined in Fig. 1. For off-glacier terrain (black triangles and curves) all medians are shown; for glaciers only autumn laser altimetry periods
New Study Maps Himalayan Glacier Behaviour
Measurements from satellites have recently provided the first overview mapping of thickness changes of Himalayan glaciers.
In a study published in Nature today, scientists assembled new datasets from Earth-observing satellites and found that glaciers in the Hindu Kush–Karakoram–Himalaya region (HKKH) lost 12 gigatonnes per year over the period 2003–08, much faster than previously reported.
The HKKH is a 2000 km-long group of mountain ranges in Asia containing about 60 000 sq km of glaciers, glacierets and perennial surface ice in varying climatic conditions. These ice masses exhibit a complex response to climate and this makes the analysis of changes in the region difficult.
Data from satellites provide a means to make these regional assessments and obtain the first spatially-resolved mass budget over the entire HKKH.
The article, ‘Contrasting patterns of early 21st-century glacier mass change in the Himalayas’ outlined a study, supported by ESA through its Globglacier and Glacier_cci projects, where laser altimeter data from NASA’s ICESat mission were combined with a digital elevation model from the Shuttle Radar Topography Mission and optical data from the Landsat mission to map glacial thickness changes in HKKH for 2003–09.
Himalaya elevation differences
The laser altimeter data were extracted for different types of glacier surfaces derived from the Landsat data and compared with the digital elevation model to obtain elevation differences over time.
On average, HKKH glaciers thinned by 0.26 m per year but there were significant subregional variations related to different climate and glaciology patterns.
In the Jammu–Kashmir subregion, thinning rates reached around 0.66 m per year, while further north and west, in the Karakoram region, they were nearly ten times slower. These findings were unaffected by glacier type (such as debris covered or clean ice).
The melting contributes to about 1% of the global sea level rise – a small contribution and only 3–4% of the total contribution from global glaciers and ice caps.
However, glacial runoff, or lack thereof, has a direct effect on the nearby Indus and Ganges River basins and is very important for lower-lying regions where there is a very large human population. The changes in mass of the glaciers contributed between 2% and 3.5% of the total discharge into these rivers, while in the Upper Indus basin the contribution was almost 10% of the annual river discharge.
The team is continuing to monitor glaciers through the Glaciers_cci project by combining 30 years of archived data with new information from present and future satellite missions, such as the Sentinel family of satellites being developed for Europe’s Global Monitoring for Environment and Security (GMES) programme.
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