Search Results (3)

Satellite-based long-term observations of vegetation cover development in combination with recent in-situ observations provide a basis to better understand the spatio-temporal changes of vegetation patterns, their sensitivity to climate drivers and thus climatic impact on proglacial landscape development. In this study we combined field investigations in the glacier forelands of Fürkele-, Zufall- and Langenferner (Ortles-Cevedale group/Eastern Italian Alps) with four different Vegetation Indices (VI) from Landsat scenes in order to test the suitability for modelling an area-wide vegetation cover map by using a Bayesian beta regression model (RStan). Since the model with the Normalized Difference Vegetation Index (NDVI) as predictor showed the best results, it was used to calculate a vegetation cover time series (1986–2019). The alteration of the proglacial areas since the end of the Little Ice Age (LIA) was analyzed from digital elevation models based on Airborne Laser Scanning (ALS) data and areal images, orthophotos, historical maps and field mapping campaigns. Our results show that a massive glacier retreat with an area loss of 8.1 km² (56.9%; LIA–2019) resulted in a constant enlargement of the glacier forelands, which has a statistically significant impact on the degree of vegetation cover. The area covered by vegetation increased from 0.25 km² (5.6%) in 1986 to 0.90 km² (11.2%) in 2019 with a significant acceleration of the mean annual changing rate. As patterns of both densification processes and plant colonization at higher elevations can be reflected by the model results, we consider in-situ observations combined with NDVI time series to be powerful tools for monitoring vegetation cover changes in alpine proglacial areas. Full article

Monitoring precipitation in mountainous areas using traditional tipping-bucket rain gauges (TPB) has become challenging in sites with strong variations of air temperature and wind speed (Ws). The drop size distributions (DSD), amount, and precipitation-type of a Parsivel OTT² disdrometer installed at 4730 m above sea level (close to the 0 °C isotherm) in the glacier foreland of the Antisana volcano in Ecuador are used to analyze the precipitation type. To correct the DSDs, we removed spurious particles and shifted fall velocities such that the mean value matches with the fall velocity–diameter relationship of rain, snow, graupel, and hail. Solid (SP) and liquid precipitation (LP) were identified through −1 and 3 °C thresholds and then grouped into low, medium, and high Ws categories by k-means approach. Changes in DSDs were tracked using concentration spectra and particle’s contribution by diameter and fall velocity. Thus, variations of concentration/dispersion and removed hydrometeors were linked with Ws changes. Corrected precipitation, assuming constant density (1 g cm⁻³), gives reliable results for LP with respect to measurements at TPB and overestimates SP measured in disdrometer. Therefore, corrected precipitation varying density models achieved fewer differences. These results are the first insight toward the understating of precipitation microphysics in a high-altitude site of the tropical Andes. Full article

The study presents findings from comparative analyses of high-resolution differential digital elevation models (DEM of Difference—DoD) based on terrestrial laser scanning (TLS) surveys. The research was conducted on the 0.2 km² Scottbreen valley glacier foreland located in the north-western part of Wedel-Jarlsberg Land (Svalbard) in August of 2013. The comparison between DTMs at 3-week intervals made it possible to identify erosion and depositional areas, as well as the volume of the melting glacier’s terminus. It showed a considerable recession rate of the Scottbreen (20 m year⁻¹) while its forefield was being reshaped by the proglacial Scott River. A study area of 205,389 m², 31% of which is occupied by the glacier (clear ice zone), was included in the repeated TLS survey, which was performed from five permanent scan station points (registered on the basis of five target points—TP). The resultant point clouds with a density ranging from 91 to 336 pt m⁻² were converted into DEMs (at a spacing of 0.1 m). They were then put together to identify erosion and depositional areas using Geomorphic Change Detection Software (GCD). During the 3-week interval, the retreat of the glacier’s snout ranged from 3 to 9 m (mean of 5 m), which was accompanied by an average lowering of the surface by up to 0.86 m (±0.03 m) and a decrease of ice volume by 53,475 m³ (±1761 m³). The deglaciated area increased by 4549 m² (~5%) as a result of the recession, which resulted in an extensive reshaping of the recently deglaciated area. The DEM of Difference (DoD) analyses showed the following: (i) lowering of the glacial surface by melting and ii) predominance of deposition in the glacier’s marginal zone. In fact, 17,570 m³ (±1172 m³) of sediments were deposited in the glacier forefield (41,451 m²). Also, the erosion of sediment layers having a volume of 11,974 m³ (±1313 m³) covered an area equal to 46,429 m² (53%). This occurrence was primarily based on the washing away of banks and the deepening of proglacial stream beds, as well as the washing away of the lower parts of moraine hillocks and outwash fans. Full article