Himalayan Glaciers Climate Change, Water Resources, and Water Security (2012) / Chapter Skim
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2 Physical Geography
2 Physical Geography
Pages 15-48
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From page 15... ...
GLACIAL MASS BALANCE The fundamentals of glacial behavior can be read ily understood by recognizing that glaciers have both Glacial ice is characterized by (a) a density between a zone of accumulation in which the volume of the about 830 and 920 kg m-3 (83 to 92 percent water glacier grows and a zone of ablation in which volume content)
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From page 16... ...
streams, rivers, and groundwater channels, and extracis the elevation where the accumulation and ablation tion by humans. When water input sources equal water zones meet and where the annual net mass balance output sources, the lake is in steady state and the lake is zero (Figure 2.2)
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From page 17... ...
If in a negative mass balance and glacial retreat. A glacier a glacial mass balance is negative, then glacial wastage that is in disequilibrium with a warming climate will is defined as the volume of icemelt that exceeds the retreat until equilibrium is reestablished or the glacier water equivalent of the annual volume of snow accudisappears.
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From page 18... ...
long-term glaciological mass balance records for the An understanding of ice dynamics is required to HKH region, and few measurements of glacial mass understand the response of glaciers to climate change balance at all (Kaser et al., 2006)
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From page 19... ...
. The differences are small, but they suggest that glacial retreat would be more sensi 4 A large mountain system located in Central Asia and to the tive to changes in climate in the Indus Basin than in north of this report's study area.
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general trends in the HKH region. In a study of gla Rates of glacial retreat in the HKH are not well ciers in northern India, Kulkarni et al.
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From page 21... ...
Therefore, use of GRACE satellite data 5,000- to 6,000-m-elevation band. Comparing the two basins, for mass balance measurements in the HKH region leads to sub- the Indus Basin has a greater proportion of its glacier area below stantial uncertainties (e.g., Bolch et al., 2012)
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From page 22... ...
been observed in Karakoram glaciers, but more field The Committee cannot state with certainty whether observations are needed to confirm whether this indi- major changes in either rates of glacial retreat or glacial cates a positive mass balance. Data from the late 1980s extent in the HKH region will occur for the next several indicated a possible trend of negative mass balance for decades.
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From page 23... ...
More precipitation phase data are needed to fully understand whether snowfall events in the region are changing and how such changes will affect glacial mass balance. With the right conditions, accelerated rates of glacial retreat beyond present rates are a possibility.
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From page 24... ...
west, and the Thar Desert of northwestern India to the Aerosols from natural sources such as desert dusts have south. It has a relatively dry climate, with annual pre- been known to coexist with the Indian monsoon in the cipitation of 400 to 600 mm, primarily from wintertime eastern HKH region for a long time.
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From page 25... ...
and vertical distributions across the Tibetan Plateau from CALIPSO (lower panel, horizontal scale shows latitude/longitude coordinates) show the deep and extended layer of aerosols over vast regions of the Indo-Gangetic Plain and Himalayan foothills.
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From page 26... ...
and vertical distributions across the Himalayan Tibetan Plateau from CALIPSO (lower panel, horizontal scale shows latitude/ longitude coordinates) show high concentration of aerosols confined within the shallow boundary layer over the Indo-Gangetic Plain and Himalayan foothills.
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From page 27... ...
. absorbing aerosols may cause early melting of snow- Surface observations of the amount of black carbon pack and accelerated glacial retreat is the so-called snow-darkening effect.
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From page 28... ...
Satellite remote sensing data have revealed critical Current Trends and Projections spatial and temporal information regarding temperaof Regional Climate ture and precipitation changes in recent decades in the HKH region. Microwave satellite measurements have Reports of surface air temperature and precipi- revealed a widespread warming trend in the tropotation trends vary greatly across the Himalayas.
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From page 29... ...
There is high coherence between interannual variations of tropospheric temperature and aerosol index for absorbing aerosols over the Himalayan foothills and the Indo-Gangetic Plain, with both temperature and aerosol showing a steady rising trend between 1979 and 2007. SOURCE: Gautam et al.
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From page 30... ...
Other stud- and will further affect the Asian monsoon and Himaies have indicated a weakening of the monsoon, with a layan glacial retreat in the future remain subjects of trend of fewer rain days over the latter half of the 20th ongoing research. One scenario is that unless effective century (Dash et al., 2009; Meehl et al., 2008; Ramesh emission control on black carbon is achieved, the conand Goswami, 2007)
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From page 31... ...
. It appears that both global out the region and in all seasons, with greater magni- and regional models are somewhat more consistent tude over the Tibetan Plateau than over the South in projecting an increase in the frequency of extreme Asian continent south of the Himalayas (Figure 2.11)
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From page 32... ...
. These projections show warming throughout the region and in all seasons, with greater magnitude over the Tibetan Plateau than over the South Asian continent south of the Himalayas.
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From page 33... ...
For example, the HKH region because they are annually resolved and Benn and Owen (1998) used moraine dating in the exactly dated, making them useful for direct calibration Kunlun Mountains along the northern edge of the and reconstruction of instrumental climate data back Tibetan Plateau to determine that during the last gla- in time.
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From page 34... ...
For each of these topics, the review of tree-ring layas have been trending opposite to predominantly evidence for climate change then proceeds from the spring temperatures in recent decades. It is unclear western to eastern ends of the HKH and up onto the why this appears to be happening, although the cooling eastern end of the Tibetan Plateau.
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From page 35... ...
Comparisons made to other tree-ring reconstructions (e.g., Bräuning and Mantwill, 2004; Fan et al., 2008a; Li et al., 2011; Liang et al., 2008, 2009) from the Tibetan Plateau also yield conflicting evidence for widespread climate warming in the 20th century.
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From page 36... ...
for the spring temperatures have generally declined there since HKH region. Three are from the Tibetan Plateau, and the mid-20th century based on tree-ring evidence.
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From page 37... ...
The Dunde to the top of these records (except for Naimona'nyi and Guliya ice cores located on the most northeastern where the most recent part of the record is missing) and northwestern areas of the Tibetan Plateau contain the 18O averages have increased by 0.71, 1.35, 20 times higher dust concentration than that of the 1.08, and 2.63 for Dunde, Puruogangri, Guliya, most southern ice-core study site, Dasuopu, at the top
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From page 38... ...
The ice-core data files along with the metadata have rather similar annual net mass balances, averagfiles for Dunde, Guliya, Dasuopu, and Puruogangri ing 220 mm water equivalent (liquid water obtained ice cores are archived at the National Climatic Data from melting snow or ice) per year for Guliya in the Center (NCDC)
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From page 39... ...
The 2,000-year perspective from these Tibetan Plateau ice cores shows large and unusual Barnett et al.
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From page 40... ...
(2008) suggested that reports of the relationship between glacial retreat Glaciers are only one part of the complex HKH and downstream water resources have not accounted hydroclimate system,12 where the relative importance for mass loss through thinning of high-elevation, low- of the contribution of glacial meltwater to runoff latitude glaciers.
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From page 41... ...
In a direct comparison between elevations is snowmelt and/or icemelt from elevations glacial meltwater and runoff downriver, the volume greater than 2,000 m. The values for the Ganges are contribution from glaciers can be overestimated with remarkably similar to those of Alford et al.
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From page 42... ...
These two periods are reasonably the hydrological science community (NRC, 2012a) consistent with periods of observed glacial retreat in and the HKH region is no exception; the mechanisms 1985 to 1995 and expansion in 1997 to 2002 in the and pathways of groundwater recharge and discharge Karakoram (Hewitt, 2005)
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From page 43... ...
The effect of glacial melt on ground- combined with daily rainfall and discharge measurewater recharge on the plains is likely small because the ments found that groundwater flow through bedrock contribution of glacial meltwater to flows downstream is approximately six times the annual contribution from is generally small, and therefore any groundwater glacial icemelt and snowmelt to central Himalayan rivrecharge from major rivers downstream would be little ers (Andermann et al., 2012)
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From page 44... ...
Snowmelt in the mountains surrounding graph of large rivers in the HKH region in response Kabul Basin, particularly the Paghman Mountains, to changes in climate and potential glacial retreat over contributes an unknown but important amount to the the next several decades. If anything, there may be an water resources of the basin (Mack et al., 2010)
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From page 45... ...
With few exceptions, As discussed in Chapter 1, lack of observational every year somewhere in the region, some degree of data in the HKH region has led to misunderstandings monsoon flooding will occur, due to the uneven distriabout the effects of climate change on glacial retreat bution of monsoon rain.
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From page 46... ...
. There are two distinctly different forms of glacial lake outbursts: those that result from the collapse or overtopping of ice dams formed by the glacier itself, and those that occur when water drains rapidly from lakes FIGURE 2.17 Schematic diagram of a moraine-dammed glaformed either on the lower surface of glaciers (supragla- cial lake formed by glacial meltwater.
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From page 47... ...
However, compared with the may contribute to the rapid warming of the atmosphere, large number of glacial meltwater lakes forming and model results indicate that this may in turn contribtoday because of climate warming and glacial retreat, ute to accelerated melting of snowpack and retreat of landslide lakes are less commonly formed in the high glaciers. Black carbon deposited directly on non-debrisHimalayas (e.g., Hewitt, 1982)
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From page 48... ...
Limited streamflow glacial retreat depends not only on temperature, but data also limit the understanding of the relative contrialso on precipitation changes associated with the sum- butions of rain, snowmelt, and glacial meltwater, as well mer monsoon in the central and eastern HKH and the as groundwater recharge mechanisms in the region. winter westerlies in the western HKH.
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