Search

Saharan dust outbreaks have profound effects on ecosystems, climate, human health, and the cryosphere in Europe. However, the spatial deposition pattern of Saharan dust is poorly known due to a sparse network of ground measurements. Following the extreme dust deposition event of February 2021 across Europe, a citizen science campaign was launched to sample dust on snow over the Pyrenees and the European Alps. This somewhat improvised campaign triggered wide interest since 152 samples were collected from the snow in the Pyrenees, the French Alps, and the Swiss Alps in less than 4 weeks. Among the 152 samples, 113 in total could be analysed, corresponding to 70 different locations. The analysis of the samples showed a large variability in the dust properties and amount. We found a decrease in the deposited mass and particle sizes with distance from the source along the transport path. This spatial trend was also evident in the elemental composition of the dust as the iron mass fraction decreased from 11 % in the Pyrenees to 2 % in the Swiss Alps. At the local scale, we found a higher dust mass on south-facing slopes, in agreement with estimates from high-resolution remote sensing data. This unique dataset, which resulted from the collaboration of several research laboratories and citizens, is provided as an open dataset to benefit a large community and to enable further scientific investigations. Data presented in this study are available at https://doi.org/10.5281/zenodo.7969515 (Dumont et al., 2022a).

The mountains of the Iberian peninsula host seasonal snowpacks in various environments, from mediterranean climate in the Sierra Nevada to alpine climate in the Pyrenees. This range of conditions is expected to result in different, but largely unknown, sensitivity of the snowpacks to the ongoing and future climate change. We modeled the snowpack in five sites which were selected over the peninsula for their environmental importance as indicated by their national park status. We downscaled the EURO-CORDEX meteorological forcings on a 250 m grid and forced SnowModel to obtain an ensemble of spatialized snowpack simulations over the historical period (1970-2005) and a projection period (2005-2100) considering different RCP scenarios. The accuracy of the simulation was evaluated with satellite snow cover images and in-situ measurements. The general decrease in snowpack impacts the hydrological cycle temporality and the frequency of snow droughts in the basins but is modulated by the varying climatic conditions between the study sites.

The presence of a ski resort modifies the snow cover at the local scale, due to snow management practices on ski slopes, especially grooming and snowmaking, which affect the quantity and physical behavior of the snowpack. Snow management exerts two-fold disturbances to the local hydrological cycle, through (i) uptake of water used for snowmaking, either directly after uptake or following temporary storage and (ii) changes in water runoff due to added snow mass through snowmaking and/or delayed melting of the snowpack due to snow grooming. This induces a local pressure on water resources that can be substantial in places and fuels controversies regarding the environmental impact of ski resorts. However, no scientific study to date has quantified the quantitative and qualitative disruption of the local hydrological cycle downstream, concerning both the modification of the local seasonality of the flows (e.g. low water periods) and possible modifications of the volume of water returned. Here we describe results from a case study quantifying the various components of the water budget of a small catchment (several km2), partly covered by a ski resort, in the Northern French Alps. Snow cover simulations, including the timing and amount of snowmelt, were performed using the Crocus snow cover model driven by the SAFRAN reanalysis and future climate scenarios, with and without accounting for grooming and snowmaking. Our study demonstrates a visible impact of snow grooming, through the quasi-suppression of winter snowmelt, leading to delayed snowmelt onset. Snowmaking leads to additional snowmelt amount, of the order of a few percent at the scale of the catchment, scaling with the fraction of the catchment covered by ski pistes, and the fraction of the ski pistes equipped with snowmaking. Under the situation of the case studied, there is no substantial further water loss due to snowmaking after the snow production itself, which induces about 10 % of evaporative loss of water used for snowmaking, related to the snow production process. Snowmaking mainly leads to a moderate shift in snow cover formation and snowmelt processes, to a smaller degree than the influence of future climate change on mountain hydrology. This study provides quantitative estimates of the impact of grooming and snowmaking on the hydrological regime of mountain catchments interesected by ski resorts, which can inform further studies addressing water management and climate change adaptation in mountain regions harbouring ski tourism infrastructure.

The South Col Glacier is an iconic small body of ice and snow (approx. 0.2 km2), located on the southern ridge of Mt. Everest. A recent study proposed that South Col Glacier is rapidly losing mass. This seems in contradiction with our comparison of two digital elevation models derived from aerial photographs taken in 1984 and a stereo Pléiades satellite acquisition from 2017, from which we measure a mean elevation change of 0.01 ± 0.07 m a-1. To reconcile these results we investigate wind erosion and surface energy and mass balance, and find that melt is unlikely a dominant process, contrary to previous findings.

Spatio-temporal variability of the winter surface mass balance is a major uncertainty in the modelling of annual surface mass balance. Moreover, its measurement at high spatio-temporal resolution (sub-200 m) is very useful to force, calibrate or validate models. This study presents the results of year-round field campaigns to study the evolution of the surface mass balance in a ~2 km2 portion of the accumulation zone of the Mer de Glace (France). It is based on repeated LiDAR acquisitions, submergence-velocity measurements and meteorological records. The two methods used to quantify submergence velocities show good agreement. They present a linear temporal evolution without significant seasonal changes but display significant spatial variability. We conclude that a dense network of submergence velocity measurements is required to reduce the uncertainties when computing winter and annual surface mass balance from digital elevation model differencing. Finally, a hight spatio-temporal variability of the winter surface mass balance is highlighted (e.g., a std dev. of 0.92 m in April) even though the topography is homogeneous (std dev. of 25 m). Attempts to relate this variability to different morpho-topographic variables and wind-related indexes show the need for studies conducted at the snowfall event scale to obtain a better understanding of the variability in mass balance at the glacier scale.

Rock glaciers likely play an important hydrological role in the semiarid Andes (SA; 27°–35°S). They supplement streamflow when water is needed most, especially during dry years in the late summer months. Despite their assumed importance, there are no publications that quantify their hydrological contribution to streamflow in the SA of Chile, based on measurements of rock glacier ice loss or discharge. In this study, we assess the available information on the hydrological importance of rock glaciers in the SA and provide suggestions on how future research can address knowledge gaps. We conclude that there is insufficient data available to quantify the hydrological contribution of rock glaciers in the SA. Measurements of glacier discharge are limited to unpublished data sets from which only very limited conclusions can be drawn. There are no ice volume change measurements or proxies available for individual rock glaciers. Approximations of rock glacier ice volume, calculated from areal extent, thickness, and percentage of ice content are available, and these data provide an initial baseline for calculating ice volume change in the future. While these baseline data are very valuable, they represent rough estimates due to a scarcity of studies, especially on glacier thickness and percentage of ice content. With increased temperatures and a decrease in precipitation expected in the future, rock glaciers could become an increasingly critical water resource in this region, especially in the Elqui and Juncal catchments. Improved estimates of rock glacier discharge, water content, processes, and hydrology are required to model their future evolution and evaluate their contribution to water resources.

By darkening the snow surface, mineral dust and black carbon (BC) deposition accelerate snowmelt and triggers numerous feedbacks. Assessments of their long-term impact at the regional scale are still largely missing despite the environmental and socio-economic implications of snow cover changes. Using detailed snowpack simulations, we show that dust and BC deposition advance snowmelt by 17 days on average in the French Alps and the Pyrenees over the 1979-2018 period, with major implications for water availability and ground temperature. The effect of BC compared to dust is generally prevailing except in the Southern Pyrenees more exposed to Saharan dust events. We also quantify a contribution of BC and dust deposition up to 30% to the variance of the snow melt-out date. Lastly, we demonstrate that the decrease in BC deposition since the 80's alleviated the impact of current warming on snow cover decline. Therefore, this study highlights the importance of accounting for the inter-annual fluctuations in light absorbing particles deposition to improve the accuracy of snow cover reanalyses and climate projections.

Light absorbing particles such as black carbon(BC) or mineral dust are known to darken the snow surface when deposited on the snow cover and amplify several snow-albedo feedbacks, drastically modifying the snowpack evolution and the snow cover duration. Mineral dust deposition on snow is generally more variablein time than black carbon deposition and can exhibit both a high inter and intra annual variability. In France, the Alps and the Pyrenees mountain ranges are affected by large dust deposition events originating from the Sahara . The aim of this study is to quantify the impact of these impurities on the snow cover variability over the last 39 years (1979-2018).For that purpose, the detailed snowpack model Crocus with an explicit representation of impurities is forced by SAFRAN meteorological reanalysis and a downscaling of the simulated deposition fluxes from a regional climate model (ALADIN-Climate). Different simulations are performed: (i) considering dust and/or BC (i.e. explicit representation), (ii) without impurities and (iii) considering an implicit representation (i.e. empirical parameterization based on a decreasing law of the albebo with snow age).Simulations are compared at point scale to the snow depth measured at more than 200 Meteo-France’s stations in each massif, and spatially evaluated over the 2000-2018 period in comparing thesnow cover area, snow cover duration and the Jacard index to MODIS snow products. Scores are generally better when considering the explicit representation of the impurities than when using the snow age as a proxy for light absorbing particles content.Results indicate that dust and BC have a significant impact on the snow cover duration with strong variations in the magnitude of the impact from one year to another and from one location to another.We also investigate the contribution of light absorbing particles depositionto snow cover inter-annual variability based on statistical approaches.

Based on an extensive dataset of surface mass balances (SMB) from four glaciers in the French Alps for the period 1995–2012 and in the framework of enhanced temperature-index models, we investigate the sensitivity of seasonal glacier SMB to temperature, solar radiation, precipitation and topographical variables. Our results reveal strong correlations between winter SMB and precipitation, although the precipitation gradient cannot explain the high-accumulation rates. Based on the available point measurements, we found no relevant relationship between winter SMB and topographical variables. Temperature was found to be the main driver of ice/snow ablation while solar radiation was found to strongly influence the spatial distribution of summer SMB. We compared the ability of several enhanced temperature-index models to accurately simulate point SMB and glacier-wide MB. Our analyses revealed that the uncertainties in the simulated annual SMB due to winter SMB uncertainties are larger than differences between models and prevented us from concluding, which model is the most suitable. In contrast with results of previous studies, including solar radiation in melt models did not improve the performances when modelling glacier-wide MB. We conclude that a classical degree-day model is sufficient to simulate the long-term glacier-wide MB if the underlying processes are not required to be resolved.

Bolivian glaciers are an essential source of fresh water for the Altiplano, and any changes they may undergo in the near future due to ongoing climate change are of particular concern. Glaciar Zongo, Bolivia, located near the administrative capital La Paz, has been extensively monitored by the GLACIOCLIM observatory in the last two decades. Here we model the glacier dynamics using the 3-D full-Stokes model Elmer/Ice. The model was calibrated and validated over a recent period (1997–2010) using four independent datasets: available observations of surface velocities and surface mass balance were used for calibration, and changes in surface elevation and retreat of the glacier front were used for validation. Over the validation period, model outputs are in good agreement with observations (differences less than a small percentage). The future surface mass balance is assumed to depend on the equilibrium-line altitude (ELA) and temperature changes through the sensitivity of ELA to temperature. The model was then forced for the 21st century using temperature changes projected by nine Coupled Model Intercomparison Project phase 5 (CMIP5) models. Here we give results for three different representative concentration pathways (RCPs). The intermediate scenario RCP6.0 led to 69 ± 7% volume loss by 2100, while the two extreme scenarios, RCP2.6 and RCP8.5, led to 40 ± 7% and 89 ± 4% loss of volume, respectively.

This study focuses on simulations of the seasonal and annual surface mass balance (SMB) of Saint-Sorlin Glacier (French Alps) for the period 1996-2015 using the detailed SURFEX/ISBA-Crocus snowpack model. The model is forced by SAFRAN meteorological reanalysis data, adjusted with AWS measurements to ensure that simulations of all the energy balance components, in particular turbulent fluxes, are accurately represented with respect to the measured energy balance. Results indicate good model performance for the simulation of summer SMB when using meteorological forcing adjusted with in-situ measurements. Model performance however strongly decreases without in-situ meteorological measurements. The sensitivity of the model to meteorological forcing indicates a strong sensitivity to wind speed, higher than the sensitivity to ice albedo. Compared to an empirical approach, the model exhibited better performance for simulations of snow and firn melting in the accumulation area and similar performance in the ablation area when forced with meteorological data adjusted with nearby AWS measurements. When such measurements were not available close to the glacier, the empirical model performed better. Our results suggest that simulations of the evolution of mass balance in the future using energy balance model required very accurate meteorological data which are not reliable from the climatic scenarios. With the current status of knowledge on meteorological variables and glacier surface roughness in the future, empirical approaches based on temperature and precipitation could be more appropriate for simulations of glaciers in the future.

By darkening the snow surface, mineral dust and black carbon (BC) deposition enhances snowmelt and triggers numerous feedbacks. Assessments of their long-term impact at the regional scale are still largely missing despite the environmental and socio-economic implications of snow cover changes. Here we show, using numerical simulations, that dust and BC deposition advanced snowmelt by 17 ± 6 days on average in the French Alps and the Pyrenees over the 1979–2018 period. BC and dust also advanced by 10-15 days the peak melt water runoff, a substantial effect on the timing of water resources availability. We also demonstrate that the decrease in BC deposition since the 1980s moderates the impact of current warming on snow cover decline. Hence, accounting for changes in light-absorbing particles deposition is required to improve the accuracy of snow cover reanalyses and climate projections, that are crucial for better understanding the past and future evolution of mountain social-ecological systems.