Abstract:
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The Langtang Valley -located in Nepal- is part of the monsoon dominated region in the central
Himalayas, and it is characterized by extreme orography and a high presence of glaciered areas.
Nevertheless, this work focuses on the upper part of the Langtang River Basin, with outlet below
the village of Kyanjing. Although the region has been object of several studies, little is known
about the snowline behavior within the valley and the factors influencing it.
This study proposes a new approach to extract the snowline data from remote sensed Landsat
TM, ETM+ scenes, taking advantage of the high spatial resolution Landsat products o↵er. A
point-scale description the snowline and its characteristics -altitude, slope, aspect, etc.- is obtained
and analyzed. Two di↵erent spatial analysis of the snowline dynamics are carried out, each one
preceded by a selection of scenes based on specific image-quality criteria. First, a monthly average
analysis looks at typical and consistent annual snowline dynamics; and second, the topic of interseasonal
variability of the snowline is addressed in greater detail. Both studies are statistically
based, aiming to provide consistent and robust results.
Results of this work show that climate -and specially precipitation- plays a great e↵ect in the
snowline altitude (SLA) characteristics and dynamics. Behavioral di↵erences of SLA for di↵erent
periods of the year are clearly observable, confirming thus the existence of four di↵erentiated
climatic seasons in the region. During winter and monsoon seasons precipitation events are stronger
and more frequent, having a greater and dominating e↵ect in the SLA. Only during pre-monsoon
and post-monsoon seasons, which are drier and more stable, the e↵ect of aspect in the SLA is
clearly observed, with systematic SLA di↵erences between di↵erently orientated slopes. Interannual
consistency of SLA dynamics is also shown in the results. Besides, the dominating e↵ect of
precipitation in the SLA makes the latter a potentially precise indicator of the precipitation events,
their frequency and magnitude. And last but not least, the upper Langtang Valley is shown to
have not only temporal but also spatial variability of the SLA. Observed latitudinal and altitudinal
SLA gradients are attributed to precipitation gradients within the catchment.
Finally, Landsat TM and ETM+ products are proved to be a powerful instrument to study
the snowline dynamics, either by analyzing the extracted data in statistically based studies, or by
combining Landsat products with other sources of data. |