Spatial and seasonal variability of the snowline elevation in the Langtang Valley in Nepal, using Landsat remotely sensed data from 1999-2013
Tutor / director / avaluadorBladé i Castellet, Ernest
Tipus de documentTesina
Condicions d'accésAccés obert
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.