29 Aug 2012
Four recent studies published in Nature and Science (Bolch et al. 2012; Gardelle et al. 2012; Kääb et al. 2012; Yao et al. 2012) strengthen the evidence for overall mass loss from glaciers in the greater Himalayan region. The studies also indicate:
These studies stand in contrast to the controversial results of Jacob et al. (2012), who found no net mass change of glaciers in the greater Himalayas.
Together, these papers provide a better picture of the regional differences in the rates of glacier change in the greater Himalayas. These differences reflect both the range of factors that affect an individual glacier’s response to climate change, and the method of detection used. Surface mass balance observations, for example, tend to be more negative than those derived from repeat elevation measurements, while regions influenced by westerly circulation patterns exhibit large variations in rates of mass loss. Using remote sensing products, an analysis of glacier area and length changes over the past 30 years showed the most extensive glacier reductions in the southeastern Himalayas, with decreased mass loss towards the Tibetan Plateau (Yao et al. 2012). These studies have also raised important questions about melt rates under debris cover, as both Kääb et al. (2012) and Gardelle et al. (2012) showed similar melt rates for clean and debris-covered ice.
Based on repeat measurements of glacier surface elevation between 2003 and 2008, the most recent paper (Kääb et al. 2012) finds overall mass losses in the Hindu-Kush Karakoram Himalaya of -210 ± 50 kg/m2/yr. These rates are more negative than previous gravity-based estimates (Jacob et al. 2012) and less negative than field-based estimates (Bolch et al. 2012; Yao et al. 2012). Kääb et al. observed glacier wastage rates between -200 kg/m2/yr and 550 kg/m2/yr in the Hindu Kush, Jammu Kashmir, and the western, central, and eastern Himalayas.
In terms of glacier change and water resources, Kääb et al. (2012) estimate that glacier mass loss contributes 3.5% and 2.0% to annual streamflows on average for the mountain catchments in the Indus and Ganges basins, respectively. For one of these mountain catchments in the Indus basin, the contribution of glacier to streamflow is estimated to be as high as 10%.
Field investigations and modelling by ICIMOD researchers and partners will help refine estimates of glacier mass change, resolve the seasonal contributions of glacier melt to streamflow, and quantify the impact of glacier wastage on downstream water resources. Substantial questions remain about the role of both debris cover and atmospheric black carbon in glacier melt, geohazards that can result from cryospheric changes, and the complex behaviour of Himalayan glaciers as an indicator of climate change.
Joseph Shea, Dorothea Stumm, Pradeep Mool, Arun Shrestha
Integrated Water and Hazards Management Programme (IWHM)
Integrated Knowledge Management and Communications
International Centre for Integrated Mountain Development (ICIMOD)