Changing Glaciers and Hydrology in Asia - Environmental Health at ...

In one recent study involving prediction, Ren et al. (2007) applied three global circulationmodels (GCMs), with warming effects based on a high emissions scenario, for 2001–30, over thegreater Himalayan region. Despite certain regional differences, all three GCMs indicated spatiallyaveraged glacier thicknessreductions ofapproximately 2 m forthe 2001–30 period, butonly for those areaslocated below 4,000 m.Rees and Collins (2006)have applied atemperature-index-basedhydro-glaciological modelin which glacierdimensions are allowedto decline with time todetermine by how muchand when climatewarming will reduceHimalayan glacierdimensions and affectFigure 2.3. Cumulative glacier mass balance (10 3 kg m -2 ) for selectedglacier systems, (left panel) and cumulative contribution (mm) to sea level(right panel), Lemke and Ren (2007).downstream river flows. Two hypothetical glaciers, of equal dimensions and initial geometries,were located within two hypothetical catchments representing the contrasting east and westclimates of the Himalaya. The model was applied from a start date of 1990 continuing for 150years with a uniform warming scenario of 0.06 o C year -1 . Flows for these glaciated catchmentsattain peaks of 150% and 170% of initial flow at around 2050 and 2070 in the west and eastrespectively, before declining until the respective hypothetical glaciers disappear in 2086 and2109. The general modeling approach is appropriate here but model inputs and glaciergeometries are hypothetical. It is assumed that melt is uniform over the total glacier surface withno distinction between specific ablation and accumulation zones; therefore, the accuracy ofresults is uncertain.In summary, where consistent results exist across various modeling efforts, they indicate littlepotential loss in total melt water available from glaciers over the next few decades. This isbecause increased temperatures could be compensated by increased precipitation falling as snowat the higher elevations, above approximately 5,000 m, as a possible result of a strengthenedIndian monsoon (Sreelata 2006).The role of black carbon in accelerating glacier meltBlack carbon emissions originate from a variety of sources, including biomass burning, residentialburning, transportation, and industry/power production; the relative amounts of each sourcediffer from region to region (USAID-Asia 2010). Black carbon strongly absorbs solar radiationand is thought to be second only to carbon dioxide as a contributor to global excess radiative22