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Understanding the role of anthropogenic emissions in glaciers retreat in the central Andes of Chile
Abstract
Glaciers in Chilean Central Andes have significatively retreated, at least, in the last 60 years. From 2004 to 2014, the largest retreat in the area (−0.15 km² yr⁻¹) was observed at Olivares Alpha Glacier (OAG). Previous glacier fluctuation studies proposed that two open-pit mines distant 7 km from the glacier could be the cause of its enhanced retreat. However, this had not been yet tested due to the lack of measured data. Here, we investigated the impact that major air pollutants emitted by local mining activities could have on the differences observed in OAG glacial retreat compared with a glacier of similar size and altitude with no nearby anthropogenic sources: Bello Glacier (BG), which has a reported lower retreat (−0.02 km² yr⁻¹). Results revealed a link between anthropogenic air pollutants and glacial retreat rates, meaning that glacial retreat is decoupled from climatic and glaciological factors. Considering that both glaciers are located in the same climatic setting, the anthropogenic air pollutants deposited onto the OAG surface appear to be forcing positive feedback in which the pollutants deposition best explain the differences in the glacier retreat. With the results of this study, it has been calculated that the impact of mining in OAG could be responsible for 82% of its total retreat since between 2004 and 2014, and only the remaining 18% would correspond to the impact of climate change.
Mining dams within urban areas are a technological risk because, in the event of an accident, theyaffect water security. For example, a sand mining dam accident caused an interruption in the watersupply in the downstream city of São José dos Campos. Thus, the social vulnerability of the populationthat suffered from a failure in the drinking water supply was evaluated. A water shortage indicator,the Social Urban Water Shortage Vulnerability Index – SUWSVI, was composed. Variables that bestreflect the socioeconomic condition were used: Average Income of Head of Household, Female Headof Household, and Children and Elderly Dependent Ratio. The sensitivity analysis considered the cityby geographic regions and zoning classes, considering infrastructure supply and lot size. The resultsshowed that although there are full water supply and sewerage infrastructure (99.6%), the access towater was unequal (39% of the population in the medium SUWSVI range).
Las transformaciones vinculadas a la búsqueda de sistemas energéticos y económicos más sostenibles pueden tener costes sociales y ecológicos que algunas comunidades y territorios deben asumir. Pueden surgir controversias asociadas al desarrollo de nuevas cadenas productivas, por ejemplo, aquellas relativas a la actividad de los “minerales de la transición”. Este estudio examina las relaciones entre la transición energética, la sociedad y el medio ambiente, centrándose en el cobre como mineral “hightech” y considerando Bolivia, Chile y Perú, tres países con economías minero-dependientes. Así, se busca descifrar si los países se están tornando más renovables, eficientes y modernos, y si esto se correlaciona con la actividad industrial asociada al cobre y factores sociales a nivel país. Como resultado, Bolivia tiene tareas pendientes tanto en la demanda como en la producción de energía. A pesar del buen desempeño en materia de renovables y eficiencia, Chile y Perú tienen tareas pendientes relacionadas con la distribución ecológica ligada a los sectores minero y energético. Las economías basadas en la minería podrían poner de manifiesto la fragilidad de las transiciones verdes en lo que respecta a alcanzar los objetivos sostenibles, teniendo en cuenta la igualdad, la justicia y el cuidado de los ecosistemas.
Transformations linked to more sustainable energy and economic systems may have societal and ecological costs, which some people and territories must assume. Controversies might emerge associated with developing new productive chains, e.g., transition mineral activity. This study examines the relations among energy transition, society, and the environment, focusing on copper as a high-tech mineral and considering Bolivia, Chile, and Peru, three countries with mining-dependent economies. This work tries to see if countries are becoming more renewable, efficient, and modern and if this correlates with copper activity and societal factors. As a result, Bolivia has pending tasks on both the energy demand and production sides. Despite presenting good performance on renewables and efficiency, Chile and Peru have pending tasks associated with the ecological distribution regarding mining and energy sectors. Mining-based economies might expose the fragility of green transitions in meeting sustainable goals considering equality, justice, and ecosystem care.
The presence of light-absorbing particles (LAPs) in snow leads to a decrease in short-wave albedo affecting the surface energy budget. However, the understanding of the impacts of LAPs is hampered by the lack of dedicated datasets, as well as the scarcity of models able to represent the interactions between LAPs and snow metamorphism. The present study aims to address both these limitations by introducing a survey of LAP concentrations over two snow seasons in the French Alps and an estimation of their impacts based on the Crocus snowpack model that represents the complex interplays between LAP dynamics and snow metamorphism. First, a unique dataset collected at Col du Lautaret (2058 m a.s.l., above sea level, French Alps) for the two snow seasons 2016–2017 and 2017–2018 is presented. This dataset consists of spectral albedo measurements, vertical profiles of snow specific surface area (SSA), density and concentrations of different LAP species. Spectral albedos are processed to estimate SSA and LAP absorption-equivalent concentrations near the surface of the snowpack. These estimates are then compared to chemical measurements of LAP concentrations and SSA measurements. Our dataset highlights, among others, large discrepancies between two measurement techniques of black carbon (BC) concentrations in snow (namely thermal-optical and laser-induced incandescence). Second, we present ensemble snowpack simulations of the multi-physics version of the detailed snowpack model Crocus, forced with in situ meteorological data, as well as dust and BC deposition fluxes from an atmospheric model. The temporal variations of near-surface LAP concentrations and SSA are most of the time correctly simulated. The simulated seasonal radiative forcing of LAPs is 33 % higher for the 2017–2018 snow season than for the 2016–2017 one, highlighting a strong variability between these two seasons. However, the shortening of the snow season caused by LAPs is similar with 10 ± 5 and 11 ± 1 d for the first and the second snow seasons, respectively. This counter-intuitive result is attributed to two small snowfalls at the end of the first season and highlights the importance in accounting for meteorological conditions to correctly predict the impact of LAPs. The strong variability of season shortening caused by LAPs in the multi-physics ensemble for the first season (10 ± 5 d) also points out the sensitivity of model-based estimations of LAP impact on modelling uncertainties of other processes. Finally, the indirect impact of LAPs (i.e. the enhancement of energy absorption due to the acceleration of the metamorphism by LAPs) is negligible for the 2 years considered here, which is contrary to what was found in previous studies for other sites.
Surface albedo typically dominates the mass balance of mountain glaciers, though long-term trends and patterns of glacier albedo are seldom explored. We calculated broadband shortwave albedo for glaciers in the central Chilean Andes (33–34°S) using end-of-summer Landsat scenes between 1986 and 2020. We found a high inter-annual variability of glacier-wide albedo that is largely a function of the glacier fractional snow-covered area and the total precipitation of the preceding hydrological year (up to 69% of the inter-annual variance explained). Under the 2010–2020 ‘Mega Drought’ period, the mean albedo, regionally averaged ranging from ~0.25–0.5, decreased by −0.05 on average relative to 1986–2009, with the greatest reduction occurring 3500–5000 m a.s.l. In 2020, differences relative to 1986–2009 were −0.14 on average as a result of near-complete absence of late summer snow cover and the driest hydrological year since the Landsat observation period began (~90% reduction of annual precipitation relative to the 1986–2009 period). We found statistically significant, negative trends in glacier ice albedo of up to −0.03 per decade, a trend that would have serious implications for the future water security of the region, because glacier ice melt acts to buffer streamflow shortages under severe drought conditions.
Black Carbon (BC) is indicated as the main atmospheric pollutant that obscures snow surfaces and absorbs solar energy, which accelerates the melting of ice/snow and produces glacier retreat. The case of Chile is of particular interest because it has most part of the Andean cryosphere, which has responded strongly to climate change through a retreat of their glaciers, having implications in the availability of freshwater for the inhabitants and economic activities. In this work, the aim was to investigate and quantify for the first time the impact that BC could have on the differences observed in the glacial retreat in the study area, decoupling this impact of the climatic and glaciological factors, through which it has not been possible to explain the difference in glacier behavior in the zone. In this case, two glaciers with comparable characteristics from the Central Andes of Chile were studied: Olivares Alpha Glacier (OAG) and Bello Glacier (BG). The spatio-temporal evolution (2004-2014) was studied using remote sensing images (Landsat). This information was analyzed together with measured data of BC concentrations in air and snow for the year 2014. Results showed important differences in glacier retreat, −27.6% for OAG vs. −5.1% for BG (2004–2014), together with a significantly higher impact of BC in OAG than BG. Regarding the sources of the measured BC, considering that both glaciers are at a similar distance from Santiago, it can be considered that there is another source influencing OAG, which could be the mountain mining activities, considering the small distance existing between this glacier and the mines.
The Andes Cordillera contains the most diverse cryosphere on Earth, including extensive areas covered by seasonal snow, numerous tropical and extratropical glaciers, and many mountain permafrost landforms. Here, we review some recent advances in the study of the main components of the cryosphere in the Andes, and discuss the changes observed in the seasonal snow and permanent ice masses of this region over the past decades. The open access and increasing availability of remote sensing products has produced a substantial improvement in our understanding of the current state and recent changes of the Andean cryosphere, allowing an unprecedented detail in their identification and monitoring at local and regional scales. Analyses of snow cover maps has allowed the identification of seasonal patterns and long term trends in snow accumulation for most of the Andes, with some sectors in central Chile and central-western Argentina showing a clear decline in snowfall and snow persistence since 2010. This recent shortage of mountain snow has caused an extended, severe drought that is unprecedented in the hydrological and climatological records from this region. Together with data from global glacier inventories, detailed inventories at local/regional scales are now also freely available, providing important new information for glaciological, hydrological, and climatological assessments in different sectors of the Andes. Numerous studies largely based on field measurements and/or remote sensing techniques have documented the recent glacier shrinkage throughout the Andes. This observed ice mass loss has put Andean glaciers among the highest contributors to sea level rise per unit area. Other recent studies have focused on rock glaciers, showing that in extensive semi-arid sectors of the Andes these mountain permafrost features contain large reserves of freshwater and may play a crucial role as future climate becomes warmer and drier in this region. Many relevant issues remain to be investigated, however, including an improved estimation of ice volumes at local scales, and detailed assessments of the hydrological significance of the different components of the cryosphere in Andean river basins. The impacts of future climate changes on the Andean cryosphere also need to be studied in more detail, considering the contrasting climatic scenarios projected for each region. The sustained work of various monitoring programs in the different Andean countries is promising and will provide much needed field observations to validate and improve the analyses made from remote sensors and modeling techniques. In this sense, the development of a well-coordinated network of high-elevation hydro-meteorological stations appears as a much needed priority to complement and improve the many glaciological and hydro-climatological assessments that are being conducted across the Andes.
As glaciers adjust their size in response to climate
variations, long-term changes in meltwater production can be expected,
affecting the local availability of water resources. We investigate glacier
runoff in the period 1955–2016 in the Maipo River basin (4843 km2,
33.0–34.3∘ S, 69.8–70.5∘ W), in the semiarid Andes of Chile.
The basin contains more than 800 glaciers, which cover 378 km2 in total (inventoried
in 2000). We model the mass balance and runoff contribution of 26 glaciers
with the physically oriented and fully distributed TOPKAPI (Topographic Kinematic Approximation and Integration)-ETH
glacio-hydrological model and extrapolate the results to the entire basin.
TOPKAPI-ETH is run at a daily time step using several glaciological and
meteorological datasets, and its results are evaluated against streamflow
records, remotely sensed snow cover, and geodetic mass balances for the
periods 1955–2000 and 2000–2013. Results show that in 1955–2016 glacier mass balance had
a general decreasing trend as a basin average but also had differences between
the main sub-catchments. Glacier volume decreased by one-fifth (from
18.6±4.5 to 14.9±2.9 km3). Runoff from the initially
glacierized areas was 177±25 mm yr−1 (16±7 % of the
total contributions to the basin), but it shows a decreasing sequence of
maxima, which can be linked to the interplay between a decrease in
precipitation since the 1980s and the reduction of ice melt. Glaciers in the
Maipo River basin will continue retreating because they are not in
equilibrium with the current climate. In a hypothetical constant climate
scenario, glacier volume would reduce to 81±38 % of the year 2000
volume, and glacier runoff would be 78±30 % of the 1955–2016
average. This would considerably decrease the drought mitigation capacity of
the basin.
Glaciers in the central Andes of Chile are fundamental freshwater sources for ecosystems and communities. Overall, glaciers in this region have shown continuous recession and down-wasting, but long-term glacier mass balance studies providing precise estimates of these changes are scarce. Here, we present the first long-term (1955–2013/2015), region-specific glacier elevation and mass change estimates for the Maipo River Basin, from which the densely populated metropolitan region of Chile obtains most of its freshwater supply. We calculated glacier elevation and mass changes using historical topographic maps, Shuttle Radar Topography Mission (SRTM), TerraSAR-X add-on for Digital Elevation Measurements (TanDEM-X), and airborne Light Detection and Ranging (LiDAR) digital elevation models. The results indicated a mean regional glacier mass balance of –0.12 ± 0.06 m w.e.a-1, with a total mass loss of 2.43 ± 0.26 Gt for the Maipo River Basin between 1955–2013. The most negative glacier mass balance was the Olivares sub-basin, with a mean value of –0.29 ± 0.07 m w.e.a-1. We observed spatially heterogeneous glacier elevation and mass changes between 1955 and 2000, and more negative values between 2000 and 2013, with an acceleration in ice thinning rates starting in 2010, which coincides with the severe drought. Our results provide key information to improve glaciological and hydrological projections in a region where water resources are under pressure.
Abstract. The presence of light-absorbing particles (LAPs) in snow leads to a decrease in shortwave albedo, affecting the surface energy budget. Precisely quantifying the impacts of LAPs on snowpack evolution is crucial to characterise the spatio-temporal variability of snowmelt and assess snow albedo feedbacks in detail. However, the understanding of the impacts of LAPs is hampered by the lack of dedicated datasets, as well as the scarcity of models able to represent the interactions between LAPs and snow metamorphism. The present study aims to address both these limitations by introducing a survey of LAP concentrations over two snow seasons in the French Alps, as well as an estimation of their impacts based on the Crocus snowpack model that represents the complex interplays between LAP dynamics and snow metamorphism.
First, we present a unique dataset collected at the Col du Lautaret (2058 m a.s.l; French Alps) for the two snow seasons 2016–2017 and 2017–2018. This dataset consists of spectral albedo measurements (manual and automated), vertical profiles of snow specific surface area (SSA), density, and concentrations of refractive Black Carbon (rBC), Elemental Carbon (EC) and mineral dust. Spectral albedo data are processed to estimate near-surface SSA and LAP absorption-equivalent concentrations near the surface of the snowpack. These estimates are then compared to chemical measurements of dust and BC concentrations, as well as to SSA measurements acquired by near-infrared reflectometry. Our dataset highlights large discrepancies between the two measurement techniques of BC concentrations, with EC concentrations being one order of magnitude higher than rBC measurements. In view of LAP absorption inferred from albedo measurements, the mass absorption efficiency (MAE) of BC used in our study (11.25 g m<sup>−2</sup> at 550 nm) is more appropriate for EC measurements than for rBC ones.
Second, we present ensemble snowpack simulations of ESCROC – the multi-physics version of the detailed snowpack model Crocus – forced with in-situ meteorological data as well as dust and BC deposition fluxes from the ALADIN-Climate atmospheric model. The results of these simulations are compared to the near-surface properties estimated from automatic albedo measurements, showing that the temporal variations of near-surface LAP concentration and SSA are correctly reproduced. The impact of dust and BC on our simulations is estimated by comparing this ensemble to a similar ensemble that does not account for LAPs. The seasonal radiative forcing of LAPs is 1.33 times higher for the 2017–2018 snow season than for the 2016–2017 one, highlighting a strong variability between these two seasons. However, the shortening of the snow season caused by LAPs are similar with 10 ± 5 and 11 ± 1 days for the first and the second snow seasons respectively. This counter-intuitive result is attributed to two small snowfalls at the end of the first season and highlights the importance to account for meteorological conditions to correctly predict the impact of LAPs. The strong variability of season shortening caused by LAPs in the multi-physics ensemble for the first season also points out the sensitivity of model-based estimations of LAP impact to modelling uncertainties of other processes. Finally, the indirect impact of LAPs (i.e. the enhancement of energy absorption due to acceleration of the metamorphism by LAPs) is negligible for the two years considered here, contrary to what was found in previous studies for other sites. This finding is mainly attributed to the meteorological conditions of the two studied snow seasons.
Changes in snow albedo (SA) on the Limari, Choapá, Aconcagua and Maipo basins of the Central Andes of Chile (CAC) are associated with the possible deposition of light-absorbing particles in the austral spring. We correlate SA with daily data of snow cover, aerosol optical depth (AOD) and land surface temperature (LST) available from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the NASA Terra satellite between 2000 and 2016, and other derived parameters such as days after albedo (DAS) and snow precipitation (SP). We used satellite pixels with 100% snow cover to obtain monthly average value of SA, LST, AOD, DAS and SP from September to November performing multiple regression analysis. We show that in Maipo, after considering LST, AOD represents an important role in changes induced to SA. The multiple regression model illustrates that AOD increases can reduce the SA during spring months by 13.59, 0.01, 0.77 and 3.8% in Limari, Choapá, Aconcagua and Maipo, respectively. In addition, we used a numerical prediction Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), showing that the black carbon distribution and average daily AOD are associated with the SA decrease of 0.15 in the Maipo basin between September 29 and 30, 2016. The WRF-Chem output showed aerosols are transported mainly with dominating westerly winds to the Limari and Maipo basins. Our results further suggest that SA decrease due to AOD may be originated in the largest industrial and urban areas in Chile, producing a negative impact on the hydrological resource, generated in the CAC.
Andean glaciers are among the fastest shrinking and largest contributors to sea level rise on Earth. They also represent crucial water resources in many tropical and semi-arid mountain catchments. Yet the magnitude of the recent ice loss is still debated. Here we present Andean glacier mass changes (from 10° N to 56° S) between 2000 and 2018 using time series of digital elevation models derived from ASTER stereo images. The total mass change over this period was −22.9 ± 5.9 Gt yr⁻¹ (−0.72 ± 0.22 m w.e. yr⁻¹ (m w.e., metres of water equivalent)), with the most negative mass balances in the Patagonian Andes (−0.78 ± 0.25 m w.e. yr⁻¹) and the Tropical Andes (−0.42 ± 0.24 m w.e. yr⁻¹), compared to relatively moderate losses (−0.28 ± 0.18 m w.e. yr⁻¹) in the Dry Andes. Subperiod analysis (2000–2009 versus 2009–2018) revealed a steady mass loss in the tropics and south of 45° S. Conversely, a shift from a slightly positive to a strongly negative mass balance was measured between 26 and 45° S. In the latter region, the drastic glacier loss in recent years coincides with the extremely dry conditions since 2010 and partially helped to mitigate the negative hydrological impacts of this severe and sustained drought. These results provide a comprehensive, high-resolution and multidecadal data set of recent Andes-wide glacier mass changes that constitutes a relevant basis for the calibration and validation of hydrological and glaciological models intended to project future glacier changes and their hydrological impacts.
Black carbon (BC) aerosols in the atmosphere strongly affect direct radiative forcing and climate, not only while suspended in the atmosphere but also after deposition onto high albedo surfaces. Snow surfaces are especially sensitive to BC deposition, because of their high surface albedo and additional positive feedbacks further enhance faster snowpack melting caused by BC deposition, resulting in modifications in water resources and recession of glaciers. For the analysis of BC deposition on snow, a precise quantification of BC mass is needed. Instead, optical methods have the potential of quantifying only BC, based on its characteristic spectral absorption. Commercial optical transmissometers commonly use quartz filters to filter BC and measure its optical attenuation. They are calibrated for the determination of BC mass concentrations in air, but not adapted or calibrated for their determination in water or snowmelt samples. Additionally, they are generally calibrated using BC-simulating materials that are not representative of ambient BC particles.
Here, a new analytical method is demonstrated for the quantitative determination of BC mass concentration in snow samples that considers filtering of melted snow with polycarbonate filters in a new device, and optical filter attenuation BC mass concentration measurement (880 nm). The attenuation can be obtained with any optical equipment that can measure the 880-nm attenuation of filters impacted with BC/snow impurities.
This method has been calibrated using real diesel vehicle exhaust soot with well-known optical properties as reference material, yielding a multipoint calibration curve for common BC concentration levels in snow. The limits of detection (0.011 mg of BC), quantification (0.036 mg of BC) and reproducibility (96.39%) of this new analytical method have been determined. Real surface snow samples collected at different locations in “Los Andes” mountains of Chile were measured with this method given a BC concentrations ranged from 151 to 5987 μg kg−1.
Central Chile, home to more than 10 million inhabitants, has experienced an uninterrupted sequence of dry years since 2010 with mean rainfall deficits of 20–40%. The so-called Mega Drought (MD) is the longest event on record and with few analogues in the last millennia. It encompasses a broad area, with detrimental effects on water availability, vegetation and forest fires that have scaled into social and economical impacts. Observations and reanalysis data reveal that the exceptional length of the MD results from the prevalence of a circulation dipole-hindering the passage of extratropical storms over central Chile—characterized by deep tropospheric anticyclonic anomalies over the subtropical Pacific and cyclonic anomalies over the Amundsen–Bellingshausen Sea. El Niño Southern Oscillation (ENSO) is a major modulator of such dipole, but the MD has occurred mostly under ENSO-neutral conditions, except for the winters of 2010 (La Niña) and 2015 (strong El Niño). Climate model simulations driven both with historical forcing (natural and anthropogenic) and observed global SST replicate the south Pacific dipole and capture part of the rainfall anomalies. Idealized numerical experiments suggest that most of the atmospheric anomalies emanate from the subtropical southwest Pacific, a region that has experienced a marked surface warming over the last decade. Such warming may excite atmospheric Rossby waves whose propagation intensifies the circulation pattern leading to dry conditions in central Chile. On the other hand, anthropogenic forcing (greenhouse gases concentration increase and stratospheric ozone depletion) and the associated positive trend of the Southern Annular Mode also contribute to the strength of the south Pacific dipole and hence to the intensity and longevity of the MD. Given the concomitance of the seemingly natural (ocean sourced) and anthropogenic forcing, we anticipate only a partial recovery of central Chile precipitation in the decades to come.
Vertical profiles of black carbon (BC) and other light-absorbing impurities were measured in seasonal snow and permanent snowfields in the Chilean Andes during Austral winters 2015 and 2016, at 22 sites between latitudes 18°S and 41°S. The samples were analyzed for spectrally-resolved visible light absorption. For surface snow, the average mass mixing ratio of BC was 15 ng/g in northern Chile (18–33°S), 28 ng/g near Santiago (a major city near latitude 33°S, where urban pollution plays a significant role), and 13 ng/g in southern Chile (33–41°S). The regional average vertically-integrated loading of BC was 207 µg/m2 in the north, 780 µg/m2 near Santiago, and 2500 µg/m2 in the south, where the snow season was longer and the snow was deeper. For samples collected at locations where there had been no new snowfall for a week or more, the BC concentration in surface snow was high (~10–100 ng/g) and the sub-surface snow was comparatively clean, indicating the dominance of dry deposition of BC. Mean albedo reductions due to light-absorbing impurities were 0.0150, 0.0160, and 0.0077 for snow grain radii of 100 µm for northern Chile, the region near Santiago, and southern Chile; respective mean radiative forcings for the winter months were 2.8, 1.4, and 0.6 W/m2. In northern Chile, our measurements indicate that light-absorption by impurities in snow was dominated by dust rather than BC.
The Echaurren Norte Glacier is a reference glacier for the World Glacier Monitoring Service (WGMS) network and has the longest time series of glacier mass balance data in the Southern Hemisphere. The data has been obtained by the direct glaciological method since 1975. In this study, we calculated glacier area changes using satellite images and historical aerial photographs, as well as geodetic mass balances for different periods between 1955 and 2015 for the Echaurren Norte Glacier in the Central Andes of Chile. Over this period, this glacier lost 65% of its original area and disaggregated into two ice bodies in the late 1990s. The geodetic mass balances were calculated by differencing digital elevation models derived from several sources. The results indicated a mean cumulative glacier wide mass loss of −40.64 ± 5.19 m w.e. (−0.68 ± 0.09 m w.e. a−1). Within this overall downwasting trend, a positive mass balance of 0.54 ± 0.40 m w.e. a−1 was detected for the period 2000–2009. These estimates agree with the results obtained with the glaciological method during the same time span. Highly negative mass change rates were found from 2010 onwards, with −1.20 ± 0.09 m w.e. a−1 during an unprecedented drought in Central Andes of Chile. The observed area and the elevation changes indicate that the Echaurren Norte Glacier may disappear in the coming years if negative mass balance rates prevail.
We present a field‐data rich modelling analysis to reconstruct the climatic forcing, glacier response and runoff generation from a high elevation catchment in central Chile over the period 2000‐2015, to provide insights into the differing contributions of debris‐covered and debris‐free glaciers under current and future changing climatic conditions. Model simulations with the physically‐based glacio‐hydrological model TOPKAPI‐ETH reveal a period of neutral or slightly positive mass balance between 2000‐2010, followed by a transition to increasingly large annual mass losses, associated with a recent mega drought. Mass losses commence earlier, and are more severe, for a heavily debris‐covered glacier, most likely due to its strong dependence on snow avalanche accumulation, which has declined in recent years. Catchment runoff shows a marked decreasing trend over the study period, but with high interannual variability directly linked to winter snow accumulation, and high contribution from ice melt in dry periods and drought conditions. The study demonstrates the importance of incorporating local‐scale processes such as snow avalanche accumulation and spatially variable debris thickness, in understanding the responses of different glacier types to climate change. We highlight the increased dependency of runoff from high Andean catchments on the diminishing resource of glacier ice during dry years.
The variables of snow cover extent (SCE), snow cover duration (SCD), and snow albedo (SAL) are primary factors determining the surface energy balance and hydrological response of the cryosphere, influencing snow pack and glacier mass-balance, melt, and runoff conditions. This study examines spatiotemporal patterns and trends in SCE, SCD, and SAL (2000–2016; 16 years) for central Chilean and Argentinean Andes using the MODIS MOD10A1 C6 daily snow product. Observed changes in these variables are analyzed in relation to climatic variability by using ground truth observations (meteorological data from the El Yeso Embalse and Valle Nevado weather stations) and the Multivariate El Niño index (MEI) data. We identified significant downward trends in both SCE and SAL, especially during the onset and offset of snow seasons. SCE and SAL showed high inter-annual variability which correlate significantly with MEI applied with a one-month time-lag. SCE and SCD decreased by an average of ~13 ± 2% and 43 ± 20 days respectively, over the study period. Analysis of spatial pattern of SCE indicates a slightly greater reduction on the eastern side (~14 ± 2%) of the Andes Cordillera compared to the western side (~12 ± 3%). The downward SCE, SAL, and SCD trends identified in this study are likely to have adverse impacts on downstream water resource availability to agricultural and densely populated regions in central Chile and Argentina.
Los glaciares constituyen reservas hídricas en estado sólido y son componentes cruciales del sistema hidrológico de montaña. A pesar de su importancia, no existía en Argentina información precisa sobre el número, ubicación y tamaño de estos cuerpos de hielo. En el año 2010, se sanciona la Ley 26639 de “Presupuestos Mínimos para la Preservación de los Glaciares y el Ambiente Periglacial”, que tiene como principales objetivos proteger los glaciares considerados como reservas estratégicas de recursos hídricos y crear el Inventario Nacional de Glaciares (ING), donde se individualicen todos los glaciares y geoformas periglaciales que actúan como reservas hídricas con toda la información necesaria para su adecuada protección, control y monitoreo. El inventario y monitoreo del estado de los glaciares y del ambiente periglacial es llevado a cabo por el Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA-CONICET) con la coordinación de la autoridad nacional de aplicación de la ley, el Ministerio de Ambiente y Desarrollo Sustentable de Argentina (MAyDS). Este inventario se realiza en tres niveles que varían en complejidad y extensión espacial. En este trabajo se presentan los resultados preliminares obtenidos en el primer nivel, que consiste en el mapeo y caracterización de glaciares (descubiertos, cubiertos, manchones de nieve y de escombros) mediante sensores remotos. Estos datos son luego verificados en el campo en sectores seleccionados. Sobre un total de 70 cuencas y subcuencas delimitadas para el inventario se ha avanzado en 64. Hasta febrero de 2017, se han inventariado 15,482 glaciares que cubren una superficie de 5743 km2
The first satellite-derived inventory of glaciers and rock glaciers in Chile, created from Landsat TM/ETM+ images spanning between 2000 and 2003 using a semi-automated procedure, is presented in a single standardized format. Large glacierized areas in the Altiplano, Palena Province and the periphery of the Patagonian icefields are inventoried. The Chilean glacierized area is 23 708 ± 1185 km², including ~3200 km² of both debris-covered glaciers and rock glaciers. Glacier distribution varies as a result of climatic gradients with latitude and elevation, with 0.8% occurring in the Desert Andes (17°30′–32° S); 3.6% in the Central Andes (32–36° S), 6.2% in the Lakes District and Palena Province (36–46° S), and 89.3% in Patagonia and Tierra del Fuego (46–56° S). Glacier outlines, across all glacierized regions and size classes, updated to 2015 using Landsat 8 images for 98 complexes indicate a decline in areal extent affecting mostly clean-ice glaciers (−92.3 ± 4.6 km²), whereas debris-covered glaciers and rock glaciers in the Desert and Central Andes appear nearly unchanged in their extent. Glacier attributes estimated from this new inventory provide valuable insights into spatial patterns of glacier shrinkage for assessing future glacier changes in response to climate change. Copyright © The Author(s) 2017 This is an Open Access article, distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives licence (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is unaltered and is properly cited.
Glaciers in the northern Patagonian Andes (35–46° S) have shown a
dramatic decline in area in the last decades. However, little is known about
glacier mass balance changes in this region. This study presents a geodetic
mass balance estimate of Monte Tronador (41.15° S;
71.88° W) glaciers by comparing a Pléiades digital elevation
model (DEM) acquired in 2012 with the Shuttle Radar Topography Mission
(SRTM) X-band DEM acquired in 2000. We find a slightly negative
Monte-Tronador-wide mass budget of −0.17 m w.e. a−1 (ranging from
−0.54 to 0.14 m w.e. a−1 for individual glaciers) and a slightly
negative trend in glacier extent (−0.16 % a−1) over the
2000–2012 period. With a few exceptions, debris-covered valley glaciers that
descend below a bedrock cliff are losing mass at higher rates, while mountain
glaciers with termini located above this cliff are closer to mass
equilibrium. Climate variations over the last decades show a notable increase
in warm season temperatures in the late 1970s but limited warming afterwards.
These warmer conditions combined with an overall drying trend may explain the
moderate ice mass loss observed at Monte Tronador. The almost balanced mass
budget of mountain glaciers suggests that they are probably approaching a
dynamic equilibrium with current (post-1977) climate, whereas the valley
glaciers tongues will continue to retreat. The slightly negative overall mass
budget of Monte Tronador glaciers contrasts with the highly negative mass
balance estimates observed in the Patagonian ice fields further south.
Light absorbing impurities (LAI) initiate powerful snow albedo feedbacks, yet due to a scarcity of observations and measurements, LAI radiative forcing is often neglected or poorly constrained in climate and hydrological models. To support physically-based modeling of LAI processes, daily measurements of dust and black carbon (BC) stratigraphy, optical grain size, snow density and spectral albedo were collected over the 2013 ablation season in the Rocky Mountains, CO. Surface impurity concentrations exhibited a wide range of values (0.02–6.0 mg g −1 pptw) with 98% of mass being deposited by three episodic dust events in April. Even minor dust loading initiated albedo decline, and the negative relationship between dust concentrations and albedo was log-linear. As melt progressed, individual dust layers coalesced and emerged at the snow surface, with minimal mass loss to meltwater scavenging. The observations show that the convergence of dust layers at the surface reduced albedo to 0.3 and snow depth declined ∼50% faster than other years with similar depth but less dust. The rapid melt led to an unexpected reduction in both grain size and density in uppermost surface layers. BC concentrations co-varied with dust concentrations but were several orders of magnitude lower (<1–20 ppb).
To improve our knowledge of glacier area changes in the central Chilean and Argentinean Andes (32°9′S–33°4′S), two new glacier inventories from 1989 to 2013/14 are compared with a reinterpreted inventory from 1955. Comparisons show glacier area retreat of 30% ± 3% since 1955, decreasing from 134 km
2
to 94 in 2013/14, whilst the annual rate of area loss showed a small increase (insignificant) between the periods of 1955–1989 and 1989–2013/2014. Separate analysis of the 1989 and 2013/14 inventories, including a larger sample, revealed a higher rate of glacier change compared with the smaller samples of these inventories. Additionally, an analysis at ~5 year intervals for six major glaciers (1955–2013) indicates large variability in response times and area loss magnitudes. Glacier Olivares Alfa, for example, lost 63% of its ice area, while the Juncal Norte Glacier lost only 10% (1955–2013). The findings from this study improve our current knowledge base concerning widespread glacier decline in the southern Andes, and furthers monitoring efforts in this poorly described region of the world, a region containing vital water resources for populated areas in South America.
Within large uncertainties in the precipitation response to greenhouse gas forcing, the Southeast Pacific drying stand out as a robust signature within climate models. A precipitation decline, of consistent direction but of larger amplitude than obtained in simulations with historical climate forcing, has been observed in central Chile since the late 1970s. To attribute the causes of this trend, we analyze local rain-gauge data and contrast them to a large ensemble of both fully-coupled and sea surface temperature-forced simulations. We show that, in concomitance with large-scale circulation changes, the Pacific Decadal Oscillation explains about half of the precipitation trend observed in central Chile. The remaining fraction is unlikely to be driven exclusively by natural phenomena but rather consistent with the simulated regional effect of anthropogenic climate change. We particularly estimate that a quarter of the rainfall deficit affecting this region since 2010 is of anthropogenic origin. An increased persistence and recurrence of droughts in central Chile emerges then as a realistic scenario under the current socioeconomic pathway.
The Central Andes of Chile and Argentina (31-35ï¿S) contain a large number and variety of ice masses, but only two surging glaciers have been studied in this region. We analyzed the 2002-2006 surge of the Horcones Inferior Glacier, Mount Aconcagua, Argentina, based on medium spatial resolution (15-30 m) satellite images and digital elevation models. During the buildup phase the glacier was stagnant, with velocities lower than 0.1 m/d. In the active-phase velocities reached 14 m/d and the glacier front advanced 3.1 km. At the peak of the active phase (2003-2004), the area-averaged elevation change was-42 m in the reservoir zone (2.53 km2) and +30 m in the receiving zone (3.31 km2). The estimated ice flux through a cross section located at 4175 meter above sea level was 108 m3 during a period of 391 days, a flux that suggests a mean glacier thickness at this location of ~90 m. The depletion phase showed a recovery of the reservoir zone elevation, the down wasting of the receiving zone (-17 m, 2007-2014), and a return to quiescent velocities. The short active phase, the abrupt change in the velocities, and the high level of the proglacial stream indicate a hydrological switch (Alaska type) trigger. The 2002-2006 and 1984-1990 surges of Horcones Inferior were synchronous with the surges of nearby Grande del Nevado Glacier. These events occurred after periods of positive mass balance, so we hypothesize a climate driver.
This article is a review of the science goals and the activities initiated within the
framework of the Pollution and its Impacts on the South American Cryosphere (PISAC)
initiative. Air pollution associated with biomass burning and urban emissions affects
extensive areas of South America. We focus on black carbon (BC) aerosol and its impacts
on air quality, water availability, and climate, with an emphasis on the Andean cryosphere.
BC is one of the key short-lived climate pollutants, which is a topic of growing interest for
near-term mitigation of these issues. Limited scientific evidence indicates that the Andean
cryosphere has already responded to climate change with receding glaciers and snow cover,
which directly affect water resources, agriculture and energy production in the Andean
region of South America. Despite the paucity of systematic observations along the Andes, a
few studies have detected BC on snow and glaciers in the Andes. These, in addition to
existing and projected emissions and weather patterns, suggest a possible contribution of
BC to the observed retreat of the Andean cryosphere. Here we provide an overview of the
current understanding of these issues from scientific and policy perspectives, and propose
strategic expansions to the relevant measurement infrastructure in the region.
Urban pollution can often impact surrounding, non-urban regions, through advection and dispersal of pollutants by the
prevailing winds. Urban regions located upstream of high mountains, such as the Andes, can potentially impact the
cryosphere by deposition of particles onto the surface of the snowpack and glaciers.
Santiago, the capital of Chile, has more than 6 million inhabitants and regularly experiences episodes of severe
pollution, particularly during the austral winter. Some studies have hypothesized that particle pollution from Santiago can
reach the cryosphere downwind of the city, but the scarcity of measurements made high in the mountains prevents the
validation of mesoscale models so the proof of actual impact remains elusive. A research project was designed to provide
some insight into this question. The Pollution Impact on Snow in the Cordillera - Experiments and Simulations (PISCES)
project was carried out in 2014 and includes both observational and modeling components. A five-week field campaign
was conducted at the end of winter, at an elevated site in a mountain valley, 65 km to the southeast of the center of
Santiago, to characterize some aspects of particulate pollution.
During synoptic conditions that result in clear days at the site, the mesoscale mountain-valley circulation is effective in
transporting pollutants upwards during the day, leading to diluted particle concentrations beyond the summits of the
highest peaks. Cloudy days with reduced up-valley circulation do not show increased concentrations associated with
transport. Back trajectories indicate that air masses reaching the site during the field campaign are seldom influenced by
pollution from Santiago.
The climate sensitivity of Abrahamsenbreen, a 20 km long surge-type glacier
in northern Spitsbergen, is studied with a simple glacier model. A scheme to
describe the surges is included, which makes it possible to account for the
effect of surges on the total mass budget of the glacier. A climate
reconstruction back to AD 1300, based on ice-core data from Lomonosovfonna
and climate records from Longyearbyen, is used to drive the model. The model
is calibrated by requesting that it produce the correct Little Ice Age
maximum glacier length and simulate the observed magnitude of the
1978 surge.
Abrahamsenbreen is strongly out of balance with the current climate. If
climatic conditions remain as they were for the period 1989–2010, the
glacier will ultimately shrink to a length of about 4 km (but this will take
hundreds of years). For a climate change scenario involving a
2 m year−1 rise of the equilibrium line from now onwards, we
predict that in the year 2100 Abrahamsenbreen will be about 12 km long.
The main effect of a surge is to lower the mean surface elevation and
thereby to increase the ablation area, causing a negative perturbation of
the mass budget. We found that the occurrence of surges leads to a faster
retreat of the glacier in a warming climate.
Because of the very small bed slope, Abrahamsenbreen is sensitive to small
perturbations in the equilibrium-line altitude. If the equilibrium line were lowered
by only 160 m, the glacier would steadily grow into
Woodfjorddalen until, after 2000 years, it would reach Woodfjord and
calving would slow down the advance.
The bed topography of Abrahamsenbreen is not known and was therefore
inferred from the slope and length of the glacier. The value of the
plasticity parameter needed to do this was varied by +20 and −20%.
After recalibration the same climate change experiments were performed,
showing that a thinner glacier (higher bedrock in this
case) in a warming climate retreats somewhat faster.
Dust deposition on surficial ice bodies is common in many areas around the world. In the high and arid northern Chilean and Argentine Andes, the public fears the dust generated by mining activities would increase ice ablation and thus decrease downstream water availability. This fear is based on a poor understanding of the complex and non-linear interaction between dust and glacier ablation as well as the uncertainties about relative contribution of glacier containing watersheds to total runoff at the point of water use. The focus of this contribution is to assess impacts to down gradient water users resulting from increases in ablation due to dust. Depending on the thickness, type, frequency of deposition and concentration of the dust on the ice surface, a net increase or decrease in ice ablation may occur. While a thin dust cover reduces the surface albedo and hence increases ablation, a thicker cover increasingly acts as thermal insulation, thus reducing ice ablation and increasing the glacier's longevity. Data from literature indicate that at less than 1 mm dust thickness ablation rates peak, resulting in ablation increases between 20 and 400 %. Field ablation tests and numerical dust distribution models for three different scenarios demonstrate that for the Andean site investigated, the downstream hydrological effects of mining-generated dust on glaciers and glacierets, at the first point of agricultural water use, are likely less than half a percent of the annual average river flow. This is largely due to the very small percent of glacial coverage upstream of the first water use point and is well below the local hydrological natural variability that is primarily driven by El Niño events.
Although black carbon (BC) is one of the key atmospheric particulate components driving climate change and air quality, there is no agreement on the terminology that considers all aspects of specific properties, definitions, measurement methods, and related uncertainties. As a result, there is much ambiguity in the scientific literature of measurements and numerical models that refer to BC with different names and based on different properties of the particles, with no clear definition of the terms. The authors present here a recommended terminology to clarify the terms used for BC in atmospheric research, with the goal of establishing unambiguous links between terms, targeted material properties and associated measurement techniques.
The large change in albedo has a great effect on glacier ablation.
Atmospheric aerosols (e.g. black carbon (BC) and dust) can reduce
the albedo of glaciers and thus contribute to their melting. In this
study, we investigated the measured albedo as well as the
relationship between albedo and mass balance in Zhadang glacier on
Mt. Nyanqentanglha associated with MODIS (10A1) data. The impacts of
BC and dust in albedo reduction in different melting conditions were
identified with SNow ICe Aerosol Radiative (SNICAR) model and
in-situ data. It was founded that the mass balance of the glacier
has a significant correlation with its surface albedo derived from
Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Terra
satellite. The average albedo of Zhadang glacier from MODIS
increased with the altitude and fluctuated but overall had
a decreasing trend during 2001–2010, with the highest (0.722) in
2003 and the lowest (0.597) in 2009 and 2010, respectively. The
sensitivity analysis via SNICAR showed that BC was a major factor in
albedo reduction when the glacier was covered by newly fallen
snow. Nevertheless, the contribution of dust to albedo reduction can
be as high as 58% when the glacier experienced strong surficial
melting that the surface was almost bare ice. And the average
radiative forcing (RF) caused by dust could increase from
1.1 to 8.6 W m−2 exceeding the
forcings caused by BC after snow was deposited and surface melting
occurred in Zhadang glacier. This suggest that it may be dust rather
than BC, dominating the melting of some glaciers in the TP during
melting seasons.
The paper is available at: http://www.sciencedirect.com/science/article/pii/S1352231012002725.
(Abstract)
"One of the major factors attributed to the accelerated melting of
Himalayan glaciers is the snow darkening effect of atmospheric black
carbon (BC). The BC is the result of incomplete fossil fuel combustion
from sources such as open biomass burning and wood burning cooking
stoves. One of the key challenges in determining the darkening effect is
the estimation uncertainty of BC deposition (BCD) rate on surface snow
cover. Here we analyze the variation of BC dry deposition in seven
different estimates based on different dry deposition methods which
include different atmospheric forcings (observations and global model
outputs) and different spatial resolutions. The seven simulations are
used to estimate the uncertainty range of BC dry deposition over the
southern Himalayas during pre-monsoon period (March-May) in 2006. Our
results show BC dry deposition rates in a wide range of 270-4700 μg
m-2 during the period. Two global models generate higher BC
dry deposition rates due to modeled stronger surface wind and
simplification of complicated sub-grid surface conditions in this
region. Using ice surface roughness and observation-based meteorological
data, we estimate a better range of BC dry deposition rate of 900-1300
μg m-2. Under dry and highly polluted conditions, aged
snow and sulfate-coated BC are expected to possibly reduce visible
albedo by 4.2-5.1%. Our results suggest that for estimating
aerosol-induced snow darkening effects of Himalaya snowpacks using
global and regional models, realistic physical representation of ice or
snow surface roughness and surface wind speed are critical in reducing
uncertainties on the estimate of BC deposition over snow surface."
With the acceleration of global warming, it has been increasingly important to investigate the roles of glaciers as freshwater sources and sensitive indicators of climate change. Thus, it is of great significance to acquire accurate information on glacier changes. However, few papers have focused on the comparison of glacier monitoring methods. The objectives of this paper are to (1) present three methods for classifying glacier boundaries, including visual interpretation, ratio between TM channels 4 and 5 as well as Normalized Difference Snow Index (NDSI); (2) compare the tree methods to give users some advice on how to choose an appropriate method; (3) analyze the relationship between glacier change and the trends of precipitation and temperature. Current distribution and glacier changes since the 1980s were mapped using multi-temporal optical remote sensing data from the Landsat series. Thematic maps were then generated using three classification methods. Furthermore, GIS-supported investigation was also conducted to get information of glacier changes. Finally, the results were compared. The results indicated that: (1) the visual interpretation method is accurate but time-consuming and operator-dependent; (2) the ratioing method using channel 4 and 5 of Landsat image is fast, accurate but need too much follow-up work; (3) NDSI cannot classify snow and glacier very well, and it sometimes misclassifies snow into glaciers; (4) analyses of precipitation and temperature indicate that global warming is a major factor affecting changes of glaciers.
Black carbon aerosol plays a unique and important role in Earth's climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms: direct solar absorption; influence on liquid, mixed phase, and ice clouds; and deposition on snow and ice. These effects are calculated with climate models, but when possible, they are evaluated with both microphysical measurements and field observations. Predominant sources are combustion related, namely, fossil fuels for transportation, solid fuels for industrial and residential uses, and open burning of biomass. Total global emissions of black carbon using bottom-up inventory methods are 7500 Gg yr(-1) in the year 2000 with an uncertainty range of 2000 to 29000. However, global atmospheric absorption attributable to black carbon is too low in many models and should be increased by a factor of almost 3. After this scaling, the best estimate for the industrial-era (1750 to 2005) direct radiative forcing of atmospheric black carbon is +0.71 W m(-2) with 90% uncertainty bounds of (+0.08, +1.27) W m(-2). Total direct forcing by all black carbon sources, without subtracting the preindustrial background, is estimated as +0.88 (+0.17, +1.48) W m(-2). Direct radiative forcing alone does not capture important rapid adjustment mechanisms. A framework is described and used for quantifying climate forcings, including rapid adjustments. The best estimate of industrial-era climate forcing of black carbon through all forcing mechanisms, including clouds and cryosphere forcing, is +1.1 W m(-2) with 90% uncertainty bounds of +0.17 to +2.1 W m(-2). Thus, there is a very high probability that black carbon emissions, independent of co-emitted species, have a positive forcing and warm the climate. We estimate that black carbon, with a total climate forcing of +1.1 W m(-2), is the second most important human emission in terms of its climate forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing. Sources that emit black carbon also emit other short-lived species that may either cool or warm climate. Climate forcings from co-emitted species are estimated and used in the framework described herein. When the principal effects of short-lived co-emissions, including cooling agents such as sulfur dioxide, are included in net forcing, energy-related sources (fossil fuel and biofuel) have an industrial-era climate forcing of +0.22 (-0.50 to +1.08) W m(-2) during the first year after emission. For a few of these sources, such as diesel engines and possibly residential biofuels, warming is strong enough that eliminating all short-lived emissions from these sources would reduce net climate forcing (i.e., produce cooling). When open burning emissions, which emit high levels of organic matter, are included in the total, the best estimate of net industrial-era climate forcing by all short-lived species from black-carbon-rich sources becomes slightly negative (-0.06 W m(-2) with 90% uncertainty bounds of -1.45 to +1.29 W m(-2)). The uncertainties in net climate forcing from black-carbon-rich sources are substantial, largely due to lack of knowledge about cloud interactions with both black carbon and co-emitted organic carbon. In prioritizing potential black-carbon mitigation actions, non-science factors, such as technical feasibility, costs, policy design, and implementation feasibility play important roles. The major sources of black carbon are presently in different stages with regard to the feasibility for near-term mitigation. This assessment, by evaluating the large number and complexity of the associated physical and radiative processes in black-carbon climate forcing, sets a baseline from which to improve future climate forcing estimates.
Deriving glacier outlines from satellite data has become increasingly popular in the past decade. In particular when glacier outlines are used as a base for change assessment, it is important to know how accurate they are. Calculating the accuracy correctly is challenging, as appropriate reference data (e.g. from higher-resolution sensors) are seldom available. Moreover, after the required manual correction of the raw outlines (e.g. for debris cover), such a comparison would only reveal the accuracy of the analyst rather than of the algorithm applied. Here we compare outlines for clean and debris-covered glaciers, as derived from single and multiple digitizing by different or the same analysts on very high- (1 m) and medium-resolution (30 m) remote-sensing data, against each other and to glacier outlines derived from automated classification of Landsat Thematic Mapper data. Results show a high variability in the interpretation of debris-covered glacier parts, largely independent of the spatial resolution (area differences were up to 30%), and an overall good agreement for clean ice with sufficient contrast to the surrounding terrain (differences ∼5%). The differences of the automatically derived outlines from a reference value are as small as the standard deviation of the manual digitizations from several analysts. Based on these results, we conclude that automated mapping of clean ice is preferable to manual digitization and recommend using the latter method only for required corrections of incorrectly mapped glacier parts (e.g. debris cover, shadow).
The geodetic method is widely used for assessing changes in the mass balance of mountain glaciers. However, comparison of repeated digital elevation models only provides a glacier volume change that must be converted to a change in mass using a density assumption or model. This study investigates the use of a constant factor for the volume-to-mass conversion based on a firn compaction model applied to simplified glacier geometries with idealized climate forcing, and two glaciers with long-term mass balance series. It is shown that the 'density' of geodetic volume change is not a constant factor and is systematically smaller than ice density in most cases. This is explained by the accretion/removal of low-density firn layers, and changes in the firn density profile with positive/negative mass balance. Assuming a value of 850 +/- 60 kg m(-3) to convert volume change to mass change is appropriate for a wide range of conditions. For short time intervals (3 yr), periods with limited volume change, and/or changing mass balance gradients, the conversion factor can however vary from 0-2000 kg m(-3) and beyond, which requires caution when interpreting glacier mass changes based on geodetic surveys.
Climate models indicate that the reduction of surface albedo caused by black-carbon contamination of snow contributes to global warming and near-worldwide melting of ice. In this study, we generated and characterized pure and black-carbon-laden snow in the laboratory and verified that black-carbon contamination appreciably reduces snow albedo at levels that have been found in natural settings. Increasing the size of snow grains in our experiments decreased snow albedo and amplified the radiative perturbation of black carbon, which justifies the aging-related positive feedbacks that are included in climate models. Moreover, our data provide an extensive verification of the Snow, Ice and Aerosol Radiation model, which will be included in the next assessment of the Intergovernmental Panel on Climate Change.
Ice and snow in the Central Andes contain significant amounts of light-absorbing particles such as black carbon. The consequent accelerated melting of the cryosphere is not only a threat from a climate perspective but also for water resources and snow-dependent species and activities, worsened by the mega-drought affecting the region since the last decade. Given its proximity to the Andes, emissions from the Metropolitan Area of Santiago, Chile, are believed to be among the main contributors to deposition on glaciers. However, no evidence backs such an assertion, especially given the usually subsident and stable conditions in wintertime, when the snowpack is at its maximum extent. Based on high-resolution chemistry-transport modeling with WRF-CHIMERE, the present work shows that, for the month of June 2015, up to 40% of black carbon dry deposition on snow or ice covered areas in the Central Andes downwind from the Metropolitan area can be attributed to emissions from Santiago. Through the analysis of aerosol tracers we determine (i) that the areas of the Metropolitan Area where emissions matter most when it comes to export towards glaciers are located in Eastern Santiago near the foothills of the Andes, (ii) the crucial role of the network of Andean valleys that channels pollutants up to remote locations near glaciers, following gentle slopes. A direct corollary is that severe urban pollution, and deposition of impurities on the Andes, are anti-correlated phenomena. Finally, a two-variable meteorological index is developed that accounts for the dynamics of aerosol export towards the Andes, based on the zonal wind speed over the urban area, and the vertical diffusion coefficient in the valleys close to ice and snow covered terrain. Numerous large urban areas are found along the Andes so that the processes studied here can shed light on similar investigations for other glaciers-dependent Andean regions.
Central Andes (33°S) represent a water-scarce region. During arid years, glacier runoff may constitute the main hydrological input at warm season and hence a steadfast deglacierization may represent a decrease in the regional water-budget. Ice-retreat enables landscape transitions from proglacial towards a paraglacial environment, allowing the formation of newly formed cryogenic deposits. Ice-surface changes in the Central Andes (33°S), including the high-mountain areas from Aconcagua, Mendoza and Maipo basins (Argentina and Chile), were studied using digitalized maps, aerial photographs, Landsat (1–8) and Sentinel-2A data for the period between 1956 and 2015. Band ratio and Normalized Difference Snow Index (NDSI) methods were tested using Landsat 8 and Sentinel-2A data for comparison. Geomorphological changes were assessed at Monos de Agua catchment (2750–4000 m a.s.l.) in the Aconcagua basin (Chile) as a regionally representative landscape transition case. Regional glacier shrinkage of 46 ± 5% between 1956 and 2016 was observed for the Central Andean sub-basins in both Argentina and Chile at 33°S. Overall, 107.1 ± 5 km² of newly exposed surfaces are subject to permafrost conditions. Such insights raise concern in terms of current and future environmental assessments for newly formed cryospheric elements in water scarce regions.
Only scarce literature exists on the effect of direct deposition of vehicle particulate matter emissions onto snow surfaces with well-quantified sources and atmospheric conditions. Local emissions from vehicles in the surroundings of ski resorts not only reduce the whiteness of the snowy landscape affecting the attractiveness to visitors, but also modify the onset of snowmelt and thus the environmental equilibrium of the local area and of the surrounding region. The changes in albedo observed at Portillo, in the Chilean Andes, were an increase of around 0.17 units after a heavy snowfall (20 cm accumulation), an increase of around 0.07 after a prolonged lighter snowfall (10 cm accumulation), and a mean decrease of around 0.08 units per day with heavy traffic (around 2000 vehicles per day). Other parameters such as wind velocity and direction did not greatly affect the snow albedo during this study because the wind direction was fairly constant due to the terrain restriction. It is difficult to estimate how much the snow metamorphism and melting contributed to the observed decrease. The albedo changes observed are helpful to confirm the close cause-effect relationship between these parameters and the snow albedo, and to foresee that traffic restriction may allow for more stable snowpack conditions. The case study presented here can be extrapolated to other vehicle-contaminated snow areas, thus examining their contribution to snow radiative forcing and climate change at multiple scale.
The evolution of the Grande del Nevado Glacier surge was documented through analysis of Landsat data, using image and computer-compatible tape formats, for 22 different dates between 1976 and 1986. Through time-lapse analysis of the sequential satellite images, it was determined that the glacier had a surge or rapid advance in 1984. The glacier front was in progress sometime between 16 February 1984 and 4 April 1984. Following an advance of 2.7 km, it dammed the Río Plomo in November 1984, creating a lake which, by January 1985, was 2.8 km long and 1.1 km wide. Fortunately, in March 1985, the lake began slowly draining through a natural subglacial tunnel, and continued outflowing until the end of this month, when the lake was no longer observable on satellite images.
Black carbon (BC) emitted from the incomplete combustion of biomass and fossil fuel impacts the climate system, cryospheric change, and human health. This study documents black carbon deposition in snow from a benchmark glacier on the northern Tibetan Plateau. Significant seasonality of BC concentrations indicates different input or post-depositional processes. BC particles deposited in snow had a mass volume median diameter slightly larger than that of black carbon particles typically found in the atmosphere. Also, unlike black carbon particles in the atmosphere, the particles deposited in snow did not exhibit highly fractal morphology by Scanning Transmission Electron Microscope. Footprint analysis indicated BC deposited on the glacier in summer originated mainly from Central Asia; in winter, the depositing air masses generally originated from Central Asia and Pakistan. Anthropogenic emissions play an important role on black carbon deposition in glacial snow, especially in winter. The mass absorption efficiency of BC in snow at 632 nm exhibited significantly seasonality, with higher values in summer and lower values in winter. The information on black carbon deposition in glacial snow provided in this study could be used to help mitigate the impacts of BC on glacier melting on the northern Tibetan Plateau.
Mass balance of a glacier is an accepted measure of how much mass a glacier gains or loses.
In theory, it is typically computed by integral functional and empirically, it is approximated by arithmetic mean.
However, the variability of such an approach was not studied satisfactory yet.
In this paper we provide a dynamical system of mass balance measurements under the constrains of 2nd order model with exponentially decreasing covariance. We also provide locations of optimal measurements, so called designs.
We study Ornstein-Uhlenbeck (OU) processes and sheets with linear drifts and introduce K optimal designs in the correlated processes setup. We provide a thorough comparison of equidistant, Latin Hypercube Samples (LHS), and factorial designs for D- and K-optimality as well as the variance. We show differences between these criteria and discuss the role of equidistant designs for the correlated process. In particular, applications to estimation of mass balance of Olivares Alfa and Beta glaciers in Chile is investigated showing that simple application of full raster design and kriging based on inter- and extrapolation of points can lead to increased variance, we also show how the removal of certain measurement points may increase the quality of the melting assessment while decreasing costs. Blow-ups of solutions of dynamical systems underline the empirically observed fact that in a homogenous glaciers around 11 well positioned stakes suffices for mass balance measurement.
Atmospheric transport of aerosols leads to deposition of impurities in snow, even in areas of the Arctic as remote as Greenland. Major ions (e.g. Na⁺, Ca²⁺, NH4⁺, K⁺, SO4²⁻) are frequently used as tracers for common aerosol sources (e.g. sea spray, dust, biomass burning, anthropogenic emissions). Trace element data can supplement tracer ion data by providing additional information about sources. Although many studies have considered either trace elements or major ions, few have reported both. This study determined total and water-soluble concentrations of 31 elements (Al, As, Ca, Cd, Ce, Co, Cr, Dy, Eu, Fe, Gd, K, La, Mg, Mn, Na, Nb, Nd, Pb, Pr, S, Sb, Si, Sm, Sn, Sr, Ti, V, U, Y, Zn) in shallow snow pits at 22 sampling sites in Greenland, along a transect from Summit Station to sites in the northwest. Black carbon (BC) and inorganic ions were measured in colocated samples. Sodium, which is typically used as a tracer of sea spray, did not appear to have any non-marine sources. The rare earth elements, alkaline earth elements (Mg, Ca, Sr), and other crustal elements (Fe, Si, Ti, V) were not enriched above crustal abundances relative to Al, indicating that these elements are primarily dust sourced. Calculated ratios of non-sea salt Ca (nssCa) to estimated dust mass affirm the use of nssCa as a dust tracer, but suggest up to 50% uncertainty in that estimate in the absence of other crustal element data. Crustal enrichment factors indicated that As, Cd, Pb, non-sea-salt S, Sb, Sn, and Zn were enriched in these samples, likely by anthropogenic sources. Principal component analysis indicated more than one crustal factor, and a variety of factors related to anthropogenically enriched elements. Analysis of trace elements alongside major tracer ions does not change interpretation of ion-based source attribution for sources that are well-characterized by ions, but is valuable for assessing uncertainty in source attribution and identifying sources not represented by major ions.
Remote sensing of light-absorbing particles (LAPs), or dark-colored impurities, such as black carbon (BC) and dust on snow is a key remaining challenge in cryospheric surface characterization and application to snow, ice and climate models. We present a quantitative data set of in situ snow reflectance, measured and modeled albedo, and BC and trace element concentrations from clean to heavily fossil fuel emission contaminated snow near South Pole, Antarctica. Over 380 snow reflectance spectra (350-2500 nm) and 28 surface snow samples were collected at 7 distinct sites in the austral summer season of 2014-2015. Snow samples were analyzed for BC concentration via a single particle soot photometer and for trace element concentration via an inductively coupled plasma mass spectrometer. Snow impurity concentrations ranged from 0.14 – 7000 ppb BC, 9.5 – 1200 ppb sulfur, 0.19 – 660 ppb iron, 0.043 – 6.2 ppb chromium, 0.13–120 ppb copper, 0.63 – 6.3 ppb zinc, 0.45 – 82 ppt arsenic, 0.0028 – 6.1 ppb cadmium, 0.062–22 ppb barium, and 0.0044 – 6.2 ppb lead. Broadband visible to shortwave infrared albedo ranged from 0.85 in pristine snow to 0.62 in contaminated snow. LAP radiative forcing, the enhanced surface absorption due to BC and trace elements, spanned from < 1 W m⁻² for clean snow to ~70 W m⁻² for snow with high BC and trace element content. Measured snow reflectance differed from modeled snow albedo due to specific impurity dependent absorption features, which we recommend be further studied and improved in snow albedo models.
Abstract
Remote sensing of light-absorbing particles (LAPs), or dark-colored impurities, such as black carbon (BC) and dust on snow is a key remaining challenge in cryospheric surface characterization and application to snow, ice and climate models. We present a quantitative data set of in situ snow reflectance, measured and modeled albedo, and BC and trace element concentrations from clean to heavily fossil fuel emission contaminated snow near South Pole, Antarctica. Over 380 snow reflectance spectra (350-2500 nm) and 28 surface snow samples were collected at 7 distinct sites in the austral summer season of 2014-2015. Snow samples were analyzed for BC concentration via a single particle soot photometer and for trace element concentration via an inductively coupled plasma mass spectrometer. Snow impurity concentrations ranged from 0.14 – 7000 ppb BC, 9.5 – 1200 ppb sulfur, 0.19 – 660 ppb iron, 0.043 – 6.2 ppb chromium, 0.13–120 ppb copper, 0.63 – 6.3 ppb zinc, 0.45 – 82 ppt arsenic, 0.0028 – 6.1 ppb cadmium, 0.062–22 ppb barium, and 0.0044 – 6.2 ppb lead. Broadband visible to shortwave infrared albedo ranged from 0.85 in pristine snow to 0.62 in contaminated snow. LAP radiative forcing, the enhanced surface absorption due to BC and trace elements, spanned from < 1 W m⁻² for clean snow to ~70 W m⁻² for snow with high BC and trace element content. Measured snow reflectance differed from modeled snow albedo due to specific impurity dependent absorption features, which we recommend be further studied and improved in snow albedo models.
In Canada's Northwest Territories, mining for base metals and diamonds are vital economic activities which carry risks of adverse environmental impacts. To gather baseline geochemical data against which the impact of future mining activities may be measured, a survey of trace metal concentrations in snow was carried out in 2012 along a 285-km stretch of winter mining road crossing the taiga-tundra ecotone between latitudes 62.8 and 65.5° N. The distribution of 17 elements, including mercury (Hg), was measured and mapped. Results indicate that road traffic along the winter road has only a modest impact on the metal content of the nearby tundra-taiga snowpack, and that this impact is largely due to the mobilization of soil dust and associated elements. However, some enrichment of As, Pb, Sr and Zn in snow was detected near former gold mine sites, likely reflecting the windborne dispersion of contaminated soils. The Hg concentrations in snow across the study area were generally low (≤3.01 ng L⁻¹), and did not covary with any other metals, which suggests atmospheric deposition from distant/diffuse sources. An analysis of air mass back-trajectories pointed to the most likely distant (>10³ km) anthropogenic source regions being eastern Asia or Russia. Using Hg data from the present survey and another source, in combination with gridded maps of snowpack water equivalent, we calculated the potential flux of atmospherically-derived Hg that could be released by spring snowmelt into the Mackenzie River to be in the order of ∼195–404 kg a⁻¹, which may represent a substantial fraction of the estimated total Hg discharge to the Beaufort Sea.
We apply the process-based, distributed TOPKAPI-ETH glacio-hydrological model to a glacierized catchment (19% glacierized) in the semiarid Andes of central Chile. The semiarid Andes provides vital freshwater resources to valleys in Chile and Argentina, but only few glacio-hydrological modelling studies have been conducted, and its dominant hydrological processes remain poorly understood. The catchment contains two debris-free glaciers reaching down to 3900 m asl (Bello and Yeso glaciers) and one debris-covered avalanche-fed glacier reaching to 3200 m asl (Piramide Glacier). Our main objective is to compare the mass balance and runoff contributions of both glacier types under current climatic conditions. We use a unique dataset of field measurements collected over two ablation seasons combined with the distributed TOPKAPI-ETH model that includes physically oriented parameterizations of snow and ice ablation, gravitational distribution of snow, snow albedo evolution and the ablation of debris-covered ice. Model outputs indicate that while the mass balance of Bello and Yeso glaciers is mostly explained by temperature gradients, the Piramide Glacier mass balance is governed by debris thickness and avalanches and has a clear non-linear profile with elevation as a result. Despite the thermal insulation effect of the debris cover, the mass balance and contribution to runoff from debris-free and debris-covered glaciers are similar in magnitude, mainly because of elevation differences. However, runoff contributions are distinct in time and seasonality with ice melt starting approximately four weeks earlier from the debris-covered glacier, what is of relevance for water resources management. At the catchment scale, snowmelt is the dominant contributor to runoff during both years. However, during the driest year of our simulations, ice melt contributes 42 ± 8% and 67 ± 6% of the annual and summer runoff, respectively. Sensitivity analyses show that runoff is most sensitive to temperature and precipitation gradients, melt factors and debris cover thickness. Copyright
Information on the snowpack content of major ions, trace metals, and organic contaminants (pesticides and total PCBs) has been reviewed and discussed. Although several limitations exist, regional snowpack surveys have been successfully used to delineate spatial trends in acidic deposition. In contrast to the annual anionic predominance of SO
42- in atmospheric deposition, NO
3- is often of a similar magnitude or even greater than SO
42- in the snowpack in locations affected by acidic deposition. Trace metal concentrations are generally greater than tenfold higher at European and North American regional locations than in Arctic or Antarctic “background” sites. The dry deposited component of the total snowpack pollutant load is generally less significant (1% to 45%) than the wet-deposited component, although there is much variability among chemical parameters and locations. There is conflicting evidence on the premelt stability of snowpacks; stability is clearly governed by many factors, and the occurrence of unfrozen underlying soils may be very important. The net radiative energy flux is primarily responsible for melting. Delivery of meltwater is often greatly complicated by the snowpack mesostructure; ice layers and the development of within-pack pipe flow can make modeling of this process very difficult. Rain-on-snow events can be very important both hydrologically and chemically. Fractionation of the pollutants during normal snowpack metamorphosis gives early meltwater ion and metal concentrations that are five- to ten-fold greater than those in the parent snow. Major ions are lost from the snowpack at differing rates during melting, a process known as preferential elution. Springtime reductions in pH, acid-neutralizing capacity, and base cations observed in surface waters occur due to both simple dilution and the differential release of snowpack pollutants. In contrast, lake and stream concentrations of Al and NO
3- typically increase, although the behavior of the latter is variable from location to location. Concentrations of SO
42- remain comparatively constant, an observation attributed to rapid excahnge of this ion in the soil environment. In lakes, the effect of snowmelt is generally limited to a near surface layer, 1 to 3 m thick. The spring melt event may hold grave consequences for several species of aquatic biota; most reported fishkill events have occurred in Scandinavia.
The evolution of the Grande del Nevado Glacier surge was documented through analysis of Landsat data, using image and computer-compatible tape formats, for 22 different dates between 1976 and 1986. Through time-lapse analysis of the sequential satellite images, it was determined that the glacier had a surge or rapid advance in 1984. The glacier front was in progress sometime between 16 February 1984 and 4 April 1984. Following an advance of 2.7 km, it dammed the Rio Plomo in November 1984, creating a lake which, by January 1985, was 2.8 km long and 1.1 km wide. Fortunately, in March 1985, the lake began slowly draining through a natural subglacial tunnel, and continued outflowing until the end of this month, when the lake was no longer observable on satellite images.
The surface energy balance and mass balance of the Greenland ice sheet depends on the albedo of snow, which governs the amount of solar energy that is absorbed. The observed decline of Greenland's albedo over the past decade(1-3) has been attributed to an enhanced growth of snow grains as a result of atmosphericwarming(1,2). Satellite observations show that, since 2009, albedo values even in springtime at high elevations have been lower than the 2003-2008 average. Here we show, using a numerical snow model, that the decrease in albedo cannot be attributed solely to grain growth enhancement. Instead, our analysis of remote sensing data indicates that the springtime darkening since 2009 stems from a widespread increase in the amount of light-absorbing impurities in snow, as well as in the atmosphere. We suggest that the transport of dust from snow-free areas in the Arctic that are experiencing earlier melting of seasonal snow cover(4) as the climate warms may be a contributing source of impurities. In our snow model simulations, a decrease in the albedo of fresh snow by 0.01 leads to a surface mass loss of 27 Gt yr(-1), which could induce an acceleration of Greenland's mass loss twice as large as over the past two decades(5). Future trends in light-absorbing impurities should therefore be considered in projections of Greenland mass loss.
The impact on snow pack albedo from local elemental carbon (EC) sources in Svalbard has been investigated for the winter of 2008. Highly elevated EC concentrations in the snow are observed around the settlements of Longyearbyen and Svea (locally >1000 ng g−1, about 200 times over the background level), while EC concentrations similar to the background level are seen around Ny-Ålesund. Near Longyearbyen and Svea, darkened snow influenced by wind transported coal dust from open coal stockpiles is clearly visible from satellite images and by eye at the ground. As a first estimate, the reduction in snow albedo caused by local EC pollution from the Norwegian settlements has been compared to the estimated reduction caused by long-range transported EC for entire Svalbard. The effect of local EC from Longyearbyen, Svea and all Norwegian settlements are estimated to 2.1%, 7.9% and 10% of the total impact of EC, respectively. The EC particles tend to stay on the surface during melting, and elevated EC concentrations due to the spring melt was observed. This accumulation of EC enhances the positive albedo feedbacks. The EC concentrations were observed to be larger in metamorphosed snow than in fresh snow, and especially around ice lenses.