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| Titel |
Differentiating rainfall, snow and glacial melt in the Sutlej Valley (western Himalaya) by distributed hydrological modeling |
| VerfasserIn |
Hendrik Wulf, Bodo Bookhagen, Dirk Scherler |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250049481
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| Zusammenfassung |
| Mountainous runoff from large rainfall, snow- and glacier-fed Himalayan rivers is essential
for water consumption, hydropower generation, and agriculture in the densely populated
Indo-Gangetic Plains. In light of steady population growth, widespread groundwater
lowering, and glacial retreat, it is crucial to assess and manage the available water resources
in this region. However, due to its remoteness, there is little ground-based meteorological and
glacial mass-balance data available and quantitative information on the different discharge
components are missing.
In this study, we quantify the water resources and discharge components for the Sutlej
River (~55,000 km2), which is the third largest river draining the Himalaya, by area. Most
rain falls during the monsoon season in summer, whereas snowfall is mainly sourced by the
winter westerlies. We model the hydrology at five positions of the Sutlej River and for four of
its tributaries. Our model captures daily runoff derived from rainfall, snow- and glacial melts
and losses due to evapotranspiration within 500x500 m grid cells. The model input is
based on remote-sensing data, which we calibrated with ground measurements. We
model snow and ice melting with a distributed enhanced temperature index model.
We use daily MODIS (MODerate Resolution Imaging Spectroradiometer) Aqua
and Terra imagery to derive fractional snow cover, surface albedo, cloud cover,
mean daily surface temperature, and evapotranspiration. Rainfall is obtained by the
TRMM (Tropical Rainfall Measuring Mission) product 3B42, which we calibrated
with 81 weather stations distributed across our study area. We mapped glaciers
using Landsat ETM+ band4/band5 ratio images and incorporated debris-covered
glacier areas based on manual mapping from high-resolution imagery from Google
Earth.
The modeled discharges yield high performance measures with Nash-Sutcliffe efficiency
values ranking between 0.7 and 0.85. Our results indicate that the discharge of the Sutlej
River at Bhakra (orogenic front) is sourced predominately by snowmelt (48%)
followed by effective rainfall (rainfall – evapotranspiration) (39%) and glacial melt
(13%). Average runoff per m2 is less than 0.2 m/yr in the high-elevated, low relief
Transhimalayan part of the Sutlej Valley, peaks at ~1.5 m/yr in the snowmelt dominated High
Himalaya, and is ~0.9 m/yr at the rainfall dominated orogenic front. The average glacial
ablation based on their surface area (2,004 km2) and contribution to Sutlej River
discharge between 2000 and 2007 is 0.82±0.14 m/yr. We estimate the average glacial
accumulation to be 0.21±0.02 m/yr, which is based on 1 m snow water equivalent (SWE)
accumulation for glacial parts with a continuous annual snow cover record. The
combined glacial ablation and accumulation result in an average net mass balance of
0.61±0.16 m/yr. By incremental summation of daily snow melt amounts we can
reconstruct the spatial SWE distribution for each year from 2001 to 2007. This
distribution highlights the peak SWE accumulation in areas of high relief and high
elevations, which amounts to a basin wide average of 0.12±0.03 m/yr in the Sutlej
Valley.
Our model allows quantifying water resources and their contribution to river discharge
within a large-scale watershed with reasonable accuracy, based on remote sensed imagery
calibrated by ground-based observations. This basic hydrological knowledge is crucial to
estimate the impact of global warming. |
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