Thursday, April 12, 2007

Impact of Himalyan glacier retreat on North Indian rivers

I'm pulling relavant informaiton from the following draft "An Overview of Glaciers, Glacier Retreat, and Subsequent Impacts in Nepal, India and China." I have not read any of the cited papers except Shresta et al 2003 and right now I'm trusting this source for the following information.

A status of the glacier inventory of Ganga-Brahmaputra basins

Basins Numbers of glaciers Glacierised area (Km2) Ice volume (km3)
Bhagirathi 238 755.0 67.0
Tista 449 706.0 40.0
Brahmaputra 161 223.0 10.0
Others 640 2378.0 -
Total 1488 4062.0 117.0
Source : Kaul et a.,1999

How much is it receding?
Retreats of Important Glaciers in the Himalayas
Glacier Location Period Avg. retreat Reference
Milam Uttaranchal 1849-1957 12.5 Vohra (1981)
Pindari Uttaranchal 1845-1966 23.0 Vohra (1981)
Gangotri Uttaranchal 1935-1976 15.0 Vohra (1981)
Gangotri Uttaranchal 1985-2001 23.0 Hasnain, et al. 2004
Bada Himachal Predesh 1890-1906 20.0 Mayekwski&Jschke Shigri (1979)
Kolhani Jammu & Kashmir 1857-1909 15.0 Mayekwski&Jeschke
Kolhani Jammu & Kashmir 1912-1961 16.0 Mayekwski & Jeschke
Machoi Jammu & Kashmir 1906-1957 8.1 Tiwari (1972)
Chota- Himachal Pradesh 1970-1989 7.5 Surender et al. (1994)

How much North Indian rivers are fed by himalyan glaciers?
Meltwater draining from these ice and snowfields is important in regulating the hydrology of the Indian sub-continent. Though it contributes only to 5 percent of total runoff, it releases water in the dry season (Upadhyay 1995).

Impact of glacier retreat on precipitation

Similar analysis on precipitation data, however, does not reveal any significant trends though
oscillatory characteristics are present in the precipitation series (Shrestha et al. 2000). Similar to
temperature, precipitation in Nepal is found to be influenced by or correlated to several large-
scale climatological phenomena including El NiƱo/Southern Oscillation, regional scale land and
sea-surface temperature changes and extreme events such as volcanic eruptions.

Impact of glacier retreat on river discharge

"More than 6,000 rivers and rivulets flow through Nepal. A comprehensive analysis of trends in
river flow has not been performed yet. However, a preliminary analysis of river discharge i.e.
trends in large outlet rivers, southern rivers and snow-fed rivers, has been carried out (Fig 15).
Among the large rivers, Karnali and Sapta Koshi show decreasing trends although the records for
Sapta Koshi are quite short. In contrast, the Narayani, another large river, displays an increasing
trend. Southern rivers do not show any trend. All of the three snow-fed rivers examined showed
declining trends in discharge. While these observations in river discharge are neither consistent
nor significant in magnitude due to the short record-lengths and high inter-annual variability in
discharge data, a separate study suggests that the number of flood days and consecutive days of
flood events are increasing."

Future impact of glacier retreat on fresh water in India (by simulation studies)
A model has been developed in joint collaboration with the Centre for Ecology and Hydrology
funded by the Department for International Development (DFID), UK under the
SAGARMATHA project (2004). This model reveals that there will be an increase in river
discharge at the beginning causing widespread flooding in the adjacent areas. But after a few
decades, this situation will reverse and water levels in these rivers will start declining to a
permanent decreased level.

This model, when run for 100 years under different climatic scenarios, shows distinct differences
in the potential impacts of deglaciation both regionally, in an E-W direction along the Himalayan
arc, and within catchments. In the upper Indus, the study sites show initial increases of between
+14 percent and +90 percent in mean flows (compared to baseline) over the first few decades of
the 100 year incremental scenario runs, which are generally followed by flows decreasing
between –30 percent and –90 percent of baseline by decade 10. For the Ganga, the response of
the river, near the headwaters in Uttarkashi is significantly different from what is seen
downstream at Allahabad. At Uttarkashi, flows peak at between +20 percent and +33 percent of
baseline within the first two decades and then recede to around –50 percent of baseline by decade
6; further downstream the deglaciation impacts are barely noticeable. In the headwaters of the
Brahmaputra, there is a general decrease in decadal mean flows for all temperature scenarios;
glaciers are few in this area and flows recede as the permanent snow cover reduces with
increasing temperatures.


NJ said...

interesting... but why are the rates of glacial recession in m/year ? I would expect a (sq.m. of glacial cover/year) or (cu.m. of ice/year) to be a better indicator of the melting of the glaciers.

Sushant said...

Interesting observation NJ. Actually the fact is that most of these studies are done through satellite and the only thing you can observe is the terminal points of a glacier.

Here is the measurement piece from the paper "Himalayan and Trans-Himalayan Glacier Fluctuations Since AD 1812, Paul A. Mayewski; Peter A. Jeschke"

Advances and retreats were deter-
mined from records of the movement of glacier termini. Due to a general absence and, in some cases, the unreliability of data concerning ice volume changes, such as downwasting and lateral spreading, the termini movements are used as the sole indication of
advance or retreat. However, where ice volume changes were interpretable, descriptions appear on the graphs. An example is Khumbu Glacier. In the Everest-Kanchenjunga area (Figure 4) whose snout remained stationary from about AD 1930 to 1956 although the glacier thinned approximately 70 m under a thick debris cover during this period (Miiller, 1958).

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