41 research outputs found
Recent mass balance of the Purogangri Ice Cap, central Tibetan Plateau, by means of differential X-band SAR interferometry
Due to their remoteness, altitude and harsh climatic conditions, little is known about the glaciological parameters of ice caps on the Tibetan Plateau. This study presents a geodetic mass balance estimate of the Purogangri Ice Cap, Tibet's largest ice field between 2000 and 2012. We utilized data from the actual TerraSAR-X mission and its add-on for digital elevation measurements and compared it with elevation data from the Shuttle Radar Topography Mission. The employed data sets are ideal for this approach as both data sets were acquired at X-band at nearly the same time of the year and are available at a fine grid spacing. In order to derive surface elevation changes we employed two different methods. The first method is based on differential synthetic radar interferometry while the second method uses common DEM differencing. Both approaches revealed a slightly negative mass budget of −44 ± 15 and −38 ± 23 mm w.eq. a<sup>−1</sup> (millimeter water equivalent) respectively. A slightly negative trend of −0.15 ± 0.01 km<sup>2</sup> a<sup>−1</sup> in glacier extent was found for the same time period employing a time series of Landsat data. Overall, our results show an almost balanced mass budget for the studied time period. Additionally, we detected one continuously advancing glacier tongue in the eastern part of the ice cap
Repeated glacial lake outburst flood threatening the oldest Buddhist monastery in north-western Nepal
Since 2004, Halji village, home of the oldest Buddhist Monastery in
north-western Nepal, has suffered from recurrent glacial lake outburst floods
(GLOFs). A sudden englacial drainage of a supraglacial lake, located at a
distance of 6.5 km from the village, was identified as the source of the
flood. The topography of the lake basin was mapped by combining differential
Global Positioning System (DGPS) measurements with a structure-from-motion
(SFM) approach using terrestrial photographs. From this model the maximum
filling capacity of the lake has been estimated as 1.06 ×10^6 m<sup>3</sup>
with a maximum discharge of 77.8 m<sup>3</sup> s<sup>−1</sup>, calculated using the
empiric Clague–Mathews formula. A simulation of the flooded area employing a
raster-based hydraulic model considering six scenarios of discharge volume
and surface roughness did not result in a flooding of the village. However,
both the village and the monastery are threatened by undercutting of the river
bank formed by unconsolidated sediments, as it already happened in 2011.
Further, the comparison of the GLOF occurrences with temperature and
precipitation from the High Asia Reanalysis (HAR) data set for the period
2001–2011 suggests that the GLOF is climate-driven rather than generated by
an extreme precipitation event. The calculation of geodetic mass balance and
the analysis of satellite images showed a rapid thinning and retreat of Halji
Glacier which will eventually lead to a decline of the lake basin. As the
basin will persist for at least several years, effective mitigation measures
should be considered. A further reinforcement of the gabion walls was
suggested as an artificial lake drainage is not feasible given the difficult
accessibility of the glacier
Periodic Glacial Lake Outburst Floods threatening the oldest Buddhist monastery in north-west Nepal
Evaluation of a distributed energy balance model for a high-altitude glacier on the Tibetan Plateau using glaciological measurements and a time-lapse camera system
Abstract HKT-ISTP 2013
B
Topography-derived variables provide insight into habitat occupancy of a cryptic snake, Bitis atropos
Understanding species’ habitat use is fundamental for conservation and management. However, quantifying habitat use for small cryptic species is limited by imperfect detection during field surveys and the lack of habitat data at meaningful spatial scales. Topographically-derived habitat variables from digital elevation models (DEMs) have the potential to overcome these limitations. Here we used DEM-derived topographic variables as fine-scale proxies for abiotic conditions to study site-occupancy patterns of the berg adder (Bitis atropos), a small-bodied cryptic viper. We carried out seven repeated field surveys across 219 hectares in a mountainous protected area in north-eastern South Africa to estimate snake detection probability and occupancy using maximum likelihood methods. Although snakes occurred across a third of the surveyed habitat, they were only detected 40% of the time during the springtime when detection was highest. Results showed that these snakes preferred north-west facing, mid and upper slopes, which are exposed to afternoon sun and presumably higher ambient energy. Our results demonstrate the value of using DEM-derived topographic variables for ecological studies where habitat data are either unavailable or inappropriate, thereby providing valuable insights into habitat use of cryptic and difficult to detect species
Longitudinal river zonation in the tropics: examples of fish and caddisflies from endorheic Awash river, Ethiopia
Primary Research PaperSpecific concepts of fluvial ecology are
well studied in riverine ecosystems of the temperate
zone but poorly investigated in the Afrotropical
region. Hence, we examined the longitudinal zonation
of fish and adult caddisfly (Trichoptera) assemblages
in the endorheic Awash River (1,250 km in length),
Ethiopia. We expected that species assemblages are
structured along environmental gradients, reflecting
the pattern of large-scale freshwater ecoregions. We
applied multivariate statistical methods to test for differences in spatial species assemblage structure and
identified characteristic taxa of the observed biocoenoses
by indicator species analyses. Fish and
caddisfly assemblages were clustered into highland
and lowland communities, following the freshwater
ecoregions, but separated by an ecotone with highest
biodiversity. Moreover, the caddisfly results suggest
separating the heterogeneous highlands into a forested
and a deforested zone. Surprisingly, the Awash
drainage is rather species-poor: only 11 fish (1
endemic, 2 introduced) and 28 caddisfly species (8
new records for Ethiopia) were recorded from the
mainstem and its major tributaries. Nevertheless,
specialized species characterize the highland forests, whereas the lowlands primarily host geographically
widely distributed species. This study showed that a
combined approach of fish and caddisflies is a
suitable method for assessing regional characteristics
of fluvial ecosystems in the tropicsinfo:eu-repo/semantics/publishedVersio
The magnetic anisotropy of basalts and its variations under oxidation of titanomagnetites
Glacier mass changes on the Tibetan Plateau 2003-2009 derived from ICESat laser altimetry measurements
Glacier mass changes are a valuable indicator of climate variability and monsoon oscillation on the underexplored Tibetan Plateau. In this study data from the Ice Cloud and Elevation Satellite (ICESat) is employed to estimate elevation and mass changes of glaciers on the Tibetan Plateau between 2003 and 2009. In order to get a representative sample size of ICESat measurements, glaciers on the Tibetan Plateau were grouped into eight climatically homogeneous sub-regions. Most negative mass budgets of - 0.77 ± 0.35 m w.e. a -1 were found for the Qilian Mountains and eastern Kunlun Mountains while a mass gain of + 0.37 ± 0.25 m w.e. a-1 was found in the westerly-dominated north-central part of the Tibetan Plateau. A total annual mass budget of - 15.6 ± 10.1 Gt a-1 was estimated for the eight sub-regions sufficiently covered by ICESat data which represents ∼80% of the glacier area on the Tibetan Plateau. 13.9 ± 8.9 Gt a-1 (or 0.04 ± 0.02 mm a-1 sea-level equivalent) of the total mass budget contributed 'directly' to the global sea-level rise while 1.7 ± 1.9 Gt a-1 drained into endorheic basins on the plateau.</p