Sensitivity analysis and implications for surface processes from a hydrological modelling approach in the Gunt catchment, high Pamir Mountains
A clear understanding of the hydrology is required to capture surface processes and potential inherent hazards in orogens. Complex climatic interactions control hydrological processes in high mountains that in their turn regulate the erosive forces shaping the relief. To unravel the hydrological cyc...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-07-01
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| Series: | Earth Surface Dynamics |
| Online Access: | http://www.earth-surf-dynam.net/3/333/2015/esurf-3-333-2015.pdf |
| Summary: | A clear understanding of the hydrology is required to capture surface
processes and potential inherent hazards in orogens. Complex climatic
interactions control hydrological processes in high mountains that in their
turn regulate the erosive forces shaping the relief. To unravel the
hydrological cycle of a glaciated watershed (Gunt River) considered
representative of the Pamir Mountains' hydrologic regime, we developed a
remote-sensing-based approach. At the boundary between two distinct climatic
zones dominated by the Westerlies and Indian summer monsoon, the Pamir Mountains
are poorly instrumented and only a few in situ meteorological and
hydrological data are available. We adapted a suitable conceptual distributed
hydrological model (J2000g). Interpolations of the few available in situ data
are inadequate due to strong, relief-induced, spatial heterogeneities.
Instead of these we use raster data, preferably from remote sensing sources depending
on availability and validation. We evaluate remote-sensing-based
precipitation and temperature products. MODIS MOD11 surface temperatures show
good agreement with in situ data, perform better than other products, and
represent a good proxy for air temperatures. For precipitation we tested
remote sensing products as well as the HAR10 climate model data and the
interpolation-based APHRODITE data set. All products show substantial
differences both in intensity and seasonal distribution with in situ data.
Despite low resolutions, the data sets are able to sustain high model
efficiencies (NSE ≥ 0.85). In contrast to neighbouring regions in the
Himalayas or the Hindu Kush, discharge is dominantly the product of snow and
glacier melt, and thus temperature is the essential controlling factor.
Eighty percent of annual precipitation is provided as snow in winter and spring contrasting
peak discharges during summer. Hence, precipitation and discharge are
negatively correlated and display complex hysteresis effects that allow for
the effect of interannual climatic variability on river flow to be inferred. We infer
the existence of two subsurface reservoirs. The groundwater reservoir
(providing 40 % of annual discharge) recharges in spring and summer and
releases slowly during autumn and winter, when it provides the only source for
river discharge. A not fully constrained shallow reservoir with very rapid
retention times buffers meltwaters during spring and summer. The negative
glacier mass balance (−0.6 m w.e. yr<sup−1</sup>) indicates glacier
retreat, which will ultimately affect the currently 30 % contribution of
glacier melt to annual stream flow. The spatiotemporal dependence of water
release from snow and ice during the annual cycle likewise implies
spatiotemporally restricted surface processes, which are essentially confined
to glaciated catchments in late summer, when glacier runoff is the only source
of surface runoff. Only this precise constraint of the hydrologic cycle in
this complex region allows for unravelling of the surface processes and natural
hazards such as floods and landslides as well as water availability in the
downstream areas. The proposed conceptual model has a tremendous importance
for the understanding of the denudation processes in the region. In the Pamirs, large
releases of running water that control erosion intensity are primarily
controlled by temperature and the availability of snow and glaciers, thus
making the region particularly sensitive to climatic variations. |
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| ISSN: | 2196-6311 2196-632X |