182 research outputs found
Linking glacier annual mass balance and glacier albedo retrieved from MODIS data
Albedo is one of the variables controlling the mass balance of temperate glaciers. Multispectral imagers, such as MODerate Imaging Spectroradiometer (MODIS) on board the TERRA and AQUA satellites, provide a means to monitor glacier surface albedo. In this study, different methods to retrieve broadband glacier surface albedo from MODIS data are compared. The effect of multiple reflections due to the rugged topography and of the anisotropic reflection of snow and ice are particularly investigated. The methods are tested on the Saint Sorlin Glacier (Grandes Rousses area, French Alps). The accuracy of the retrieved albedo is estimated using both field measurements, at two automatic weather stations located on the glacier, and albedo values derived from terrestrial photographs. For summers 2008 and 2009, the root mean square deviation (RMSD) between field measurements and the broadband albedo retrieved from MODIS data at 250 m spatial resolution was found to be 0.052 or about 10% relative error. The RMSD estimated for the MOD10 daily albedo product is about three times higher. One decade (2000â2009) of MODIS data were then processed to create a time series of albedo maps of Saint Sorlin Glacier during the ablation season. The annual mass balance of Saint Sorlin Glacier was compared with the minimum albedo value (average over the whole glacier surface) observed with MODIS during the ablation season. A strong linear correlation exists between the two variables. Furthermore, the date when the average albedo of the whole glacier reaches a minimum closely corresponds to the period when the snow line is located at its highest elevation, thus when the snow line is a good indicator of the glacier equilibrium line. This indicates that this strong correlation results from the fact that the minimal average albedo values of the glacier contains considerable information regarding the relative share of areal surfaces between the ablation zone (i.e. ice with generally low albedo values) and the accumulation zone (i.e. snow with a relatively high albedo). As a consequence, the monitoring of the glacier surface albedo using MODIS data can provide a useful means to evaluate the interannual variability of the glacier mass balance. Finally, the albedo in the ablation area of Saint Sorlin Glacier does not exhibit any decreasing trend over the study period, contrasting with the results obtained on Morteratsch Glacier in the Swiss Alps
Mesures météorologiques, hydrologiques et glaciologiques sur le glacier du Zongo : année hydrologique 2001-2002
Mesures météorologiques, hydrologiques et glaciologiques sur le glacier du Zongo : année hydrologique 2000-2001
Hydrological response of Andean catchments to recent glacier mass loss
The impacts of the accelerated glacier retreat in recent decades on glacier runoff changes are still unknown in most Andean catchments, increasing uncertainties in estimating water availability. This particularly affects the outer tropics and Dry Andes, heavily impacted by prolonged droughts. Current global estimates overlook climatic and morphometric disparities, which significantly influence model parameters, among Andean glaciers. Meanwhile, local studies have used different approaches to estimate glacier runoff in a few catchments. Improving 21st-century glacier runoff projections relies on calibrating and validating models using corrected historical climate inputs and calibrated parameters across diverse glaciological zones. Here, we simulate glacier evolution and related runoff changes between the periods 2000â2009 and 2010â2019 across 786 Andean catchments (11â282âkm2 of glacierized area, 11°âN to 55°âS) using the Open Global Glacier Model (OGGM). TerraClimate atmospheric variables were corrected using in situ data, getting a mean temperature bias by up to 2.1â°C and enhanced monthly precipitation. Glacier mass balance and volume were calibrated, where melt factor and the Glen A parameter exhibited significant alignment with varying environmental conditions. Simulation outcomes were validated against in situ data in three documented catchments (with a glacierized area >â8â%) and monitored glaciers. Our results at the Andes scale reveal an average reduction of 8.3â% in glacier volume and a decrease of 2.2â% in surface area between the periods 2000â2009 and 2010â2019. Comparing these two periods, glacier and climate variations have led to a 12â% increase in mean annual glacier melt (86.5âm3âsâ1) and a decrease in rainfall on glaciers of â2â% (â7.6âm3âsâ1) across the Andes, with both variables comprising the glacier runoff. We confirmed the utility of our corrected regional simulations of glacier runoff contribution at the catchment scale, where our estimations align with previous studies (e.g., Maipo 34°âS, Chile) as well as provide new insights on the seasonal glaciers' largest contribution (e.g., La Paz 16°âS, Bolivia) and new estimates of glacier runoff contribution (e.g., Baker 47°âS, Chile).</p
Accelerating glacier area loss across the Andes since the Little Ice Age
Andean glaciers are losing mass rapidly but a centennialâscale context to those rates is lacking. Here we show the extent of >5,500 glaciers during the Little Ice Age chronozone (LIA; c. 1,400 to c. 1,850) and compute an overall area change of â25% from then to year 2000 at an average rate of â36.5Â km2Â yrâ1 or â0.11%Â yrâ1. Glaciers in the Tropical Andes (Peru, Bolivia) have depleted the most; median â56% of LIA area, and the fastest; median â0.16%Â yrâ1. Up to 10 Ă acceleration in glacier area loss has occurred in Tropical mountain subâregions comparing LIA to 2,000 rates to postâ2000 rates. Regional climate controls interâregional variability, whereas local factors affect intraâregion glacier response time. Analyzing glacier area change by river basins and by protected areas leads us to suggest that conservation and environmental management strategies should be reâvisited as proglacial areas expand
Local environmental context drives heterogeneity of early succession dynamics in alpine glacier forefields
Glacier forefields have long provided ecologists with a model to study patterns of plant succession following glacier retreat. While plant-survey-based approaches applied along chronosequences provide invaluable information on plant communities, the âspace-for-timeâ approach assumes
environmental uniformity and equal ecological potential across sites and does not account for spatial variability in initial site conditions. Remote
sensing provides a promising avenue for assessing plant colonization dynamics using a so-called âreal-timeâ approach. Here, we combined 36Â years
of Landsat imagery with extensive field sampling along chronosequences of deglaciation for eight glacier forefields in the southwestern European
Alps to investigate the heterogeneity of early plant succession dynamics. Based on the two complementary and independent approaches, we found strong
variability in the time lag between deglaciation and colonization by plants and in subsequent growth rates and in the composition of early plant
succession. All three parameters were highly dependent on the local environmental context, i.e., neighboring vegetation cover and energy
availability linked to temperature and snowmelt gradients. Potential geomorphological disturbance did not emerge as a strong predictor of succession
parameters, which is perhaps due to insufficient spatial resolution of predictor variables. Notably, the identity of pioneer plant species was highly
variable, and initial plant community composition had a much stronger influence on plant assemblages than elapsed time since deglaciation. Overall,
both approaches converged towards the conclusion that early plant succession is not stochastic as previous authors have suggested but rather
determined by local ecological context. We discuss the importance of scale in deciphering the complexity of plant succession in glacier forefields
and provide recommendations for improving botanical field surveys and using Landsat time series in glacier forefield systems. Our work demonstrates
complementarity between remote sensing and field-based approaches for both understanding and predicting future patterns of plant succession in
glacier forefields.</p
Ground deformation and gravity variations modelled from present-day ice thinning in the vicinity of glaciers
Rock Glaciers as Water Stores in the Bolivian Andes: An Assessment of Their Hydrological Importance
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