• Energy Research

Abstract. Despite the great number and variety of glaciers in southern South America, in situ glacier mass balance records are extremely scarce and glacier–climate relationships are still poorly understood in this region. Here we use the longest (> 35 years) and most complete in situ mass balance record, available for glaciar Echaurren Norte in the Andes at ~34° S, to develop a minimal glacier surface mass balance model that relies on nearby monthly precipitation and air temperature data as forcing. This basic model is able to explain 78 % of the variance in the annual glacier mass balance record over the 1978–2013 calibration period. An attribution assessment indicates that precipitation variability constitutes the most important forcing modulating annual glacier mass balances at this site. A regionally-averaged series of mean annual streamflow records from both sides of the Andes is then used to estimate, through simple linear regression, this glacier's annual mass balance variations since 1909. The reconstruction model captures 68 % of the observed glacier mass balance variability and shows three periods of sustained positive mass balances embedded in an overall negative trend totaling almost −42 m w.eq. over the past 105 years. The three periods of sustained positive mass balances (centered in the 1920s–1930s, in the 1980s and in the first decade of the 21st century) coincide with several documented glacier advances in this region. Similar trends observed in other shorter glacier mass balance series suggest the glaciar Echaurren Norte reconstruction is representative of larger-scale conditions and could be useful for more detailed glaciological, hydrological and climatological assessments in this portion of the Andes.

Abstract. Observations of glacier mass changes are key to understanding the response of glaciers to climate change and related impacts, such as regional runoff, ecosystem changes, and global sea level rise. Spaceborne optical and radar sensors make it possible to quantify glacier elevation changes, and thus multi-annual mass changes, on a regional and global scale. However, estimates from a growing number of studies show a wide range of results with differences often beyond uncertainty bounds. Here, we present the outcome of a community-based inter-comparison experiment using spaceborne optical stereo (ASTER) and synthetic aperture radar interferometry (TanDEM-X) data to estimate elevation changes for defined glaciers and target periods that pose different assessment challenges. Using provided or self-processed digital elevation models (DEMs) for five test sites, 12 research groups provided a total of 97 spaceborne elevation-change datasets using various processing approaches. Validation with airborne data showed that using an ensemble estimate is promising to reduce random errors from different instruments and processing methods but still requires a more comprehensive investigation and correction of systematic errors. We found that scene selection, DEM processing, and co-registration have the biggest impact on the results. Other processing steps, such as treating spatial data voids, differences in survey periods, or radar penetration, can still be important for individual cases. Future research should focus on testing different implementations of individual processing steps (e.g. co-registration) and addressing issues related to temporal corrections, radar penetration, glacier area changes, and density conversion. Finally, there is a clear need for our community to develop best practices, use open, reproducible software, and assess overall uncertainty to enhance inter-comparison and empower physical process insights across glacier elevation-change studies.

La cordillère des Andes contient la cryosphère la plus diversifiée sur Terre, y compris de vastes zones couvertes de neige saisonnière, de nombreux glaciers tropicaux et extratropicaux et de nombreux reliefs de pergélisol montagneux. Ici, nous passons en revue quelques avancées récentes dans l'étude des principales composantes de la cryosphère dans les Andes, et discutons des changements observés dans la neige saisonnière et les masses de glace permanentes de cette région au cours des dernières décennies. Le libre accès et la disponibilité croissante des produits de télédétection ont considérablement amélioré notre compréhension de l'état actuel et des changements récents de la cryosphère andine, permettant un détail sans précédent dans leur identification et leur suivi à l'échelle locale et régionale. Les analyses des cartes de couverture neigeuse ont permis d'identifier les tendances saisonnières et les tendances à long terme de l'accumulation de neige pour la plupart des Andes, certains secteurs du centre du Chili et du centre-ouest de l'Argentine montrant une nette diminution des chutes de neige et de la persistance de la neige depuis 2010. Cette récente pénurie de neige de montagne a provoqué une sécheresse prolongée et sévère sans précédent dans les registres hydrologiques et climatologiques de cette région. En plus des données provenant des inventaires mondiaux des glaciers, des inventaires détaillés à l'échelle locale/régionale sont désormais également disponibles gratuitement, fournissant de nouvelles informations importantes pour les évaluations glaciologiques, hydrologiques et climatologiques dans différents secteurs des Andes. De nombreuses études largement basées sur des mesures sur le terrain et/ou des techniques de télédétection ont documenté le récent rétrécissement des glaciers dans les Andes. Cette perte de masse de glace observée a placé les glaciers andins parmi les plus grands contributeurs à l'élévation du niveau de la mer par unité de surface. D'autres études récentes se sont concentrées sur les glaciers rocheux, montrant que dans de vastes secteurs semi-arides des Andes, ces caractéristiques du pergélisol de montagne contiennent de grandes réserves d'eau douce et peuvent jouer un rôle crucial à mesure que le climat futur devient plus chaud et plus sec dans cette région. De nombreuses questions pertinentes restent cependant à étudier, notamment une meilleure estimation des volumes de glace à l'échelle locale et des évaluations détaillées de l'importance hydrologique des différentes composantes de la cryosphère dans les bassins fluviaux andins. La Cordillera de los Andes contiene la criosfera más diversa de la Tierra, incluidas extensas áreas cubiertas por nieve estacional, numerosos glaciares tropicales y extratropicales y muchos accidentes geográficos de permafrost de montaña. Aquí, revisamos algunos avances recientes en el estudio de los principales componentes de la criosfera en los Andes, y discutimos los cambios observados en la nieve estacional y las masas de hielo permanentes de esta región en las últimas décadas. El acceso abierto y la creciente disponibilidad de productos de teledetección ha producido una mejora sustancial en nuestra comprensión del estado actual y los cambios recientes de la criosfera andina, lo que permite un detalle sin precedentes en su identificación y monitoreo a escala local y regional. Los análisis de los mapas de la cubierta de nieve han permitido identificar patrones estacionales y tendencias a largo plazo en la acumulación de nieve para la mayor parte de los Andes, y algunos sectores en el centro de Chile y el centro-oeste de Argentina muestran una clara disminución de las nevadas y la persistencia de la nieve desde 2010. Esta reciente escasez de nieve de montaña ha provocado una prolongada y severa sequía que no tiene precedentes en los registros hidrológicos y climatológicos de esta región. Junto con los datos de los inventarios mundiales de glaciares, los inventarios detallados a escala local/regional ahora también están disponibles gratuitamente, proporcionando nueva información importante para las evaluaciones glaciológicas, hidrológicas y climatológicas en diferentes sectores de los Andes. Numerosos estudios basados en gran medida en mediciones de campo y/o técnicas de teledetección han documentado la reciente contracción de los glaciares en los Andes. Esta pérdida de masa de hielo observada ha colocado a los glaciares andinos entre los que más contribuyen al aumento del nivel del mar por unidad de área. Otros estudios recientes se han centrado en los glaciares de roca, lo que demuestra que en amplios sectores semiáridos de los Andes estas características de permafrost de montaña contienen grandes reservas de agua dulce y pueden desempeñar un papel crucial a medida que el clima futuro se vuelva más cálido y seco en esta región. Sin embargo, quedan por investigar muchas cuestiones relevantes, incluida una mejor estimación de los volúmenes de hielo a escala local y evaluaciones detalladas de la importancia hidrológica de los diferentes componentes de la criosfera en las cuencas fluviales andinas. 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. تحتوي جبال الأنديز كوردييرا على الغلاف الجليدي الأكثر تنوعًا على الأرض، بما في ذلك المناطق الشاسعة التي تغطيها الثلوج الموسمية، والعديد من الأنهار الجليدية الاستوائية وغير الاستوائية، والعديد من التضاريس الجبلية دائمة التجمد. نستعرض هنا بعض التطورات الحديثة في دراسة المكونات الرئيسية للغلاف الجليدي في جبال الأنديز، ونناقش التغيرات التي لوحظت في الثلوج الموسمية والكتل الجليدية الدائمة لهذه المنطقة على مدى العقود الماضية. أدى الوصول المفتوح وزيادة توافر منتجات الاستشعار عن بعد إلى تحسن كبير في فهمنا للحالة الراهنة والتغيرات الأخيرة في الغلاف الجليدي للأنديز، مما سمح بتفاصيل غير مسبوقة في تحديدها ورصدها على المستويين المحلي والإقليمي. سمحت تحليلات خرائط الغطاء الثلجي بتحديد الأنماط الموسمية والاتجاهات طويلة الأجل في تراكم الثلوج في معظم جبال الأنديز، حيث أظهرت بعض القطاعات في وسط تشيلي ووسط غرب الأرجنتين انخفاضًا واضحًا في تساقط الثلوج واستمرارها منذ عام 2010. وقد تسبب هذا النقص الأخير في الثلوج الجبلية في جفاف شديد ممتد لم يسبق له مثيل في السجلات الهيدرولوجية والمناخية من هذه المنطقة. إلى جانب البيانات المستمدة من قوائم الجرد العالمية للأنهار الجليدية، تتوفر الآن أيضًا قوائم جرد مفصلة على المستويات المحلية/الإقليمية مجانًا، مما يوفر معلومات جديدة مهمة للتقييمات الجليدية والهيدرولوجية والمناخية في قطاعات مختلفة من جبال الأنديز. وثقت العديد من الدراسات التي تستند إلى حد كبير إلى القياسات الميدانية و/أو تقنيات الاستشعار عن بعد الانكماش الأخير للأنهار الجليدية في جميع أنحاء جبال الأنديز. وقد وضع فقدان الكتلة الجليدية الملحوظ الأنهار الجليدية في الأنديز بين أعلى المساهمين في ارتفاع مستوى سطح البحر لكل وحدة مساحة. ركزت دراسات حديثة أخرى على الأنهار الجليدية الصخرية، وأظهرت أنه في القطاعات شبه القاحلة الواسعة في جبال الأنديز، تحتوي هذه المعالم الجبلية دائمة التجمد على احتياطيات كبيرة من المياه العذبة وقد تلعب دورًا حاسمًا حيث يصبح المناخ المستقبلي أكثر دفئًا وجفافًا في هذه المنطقة. ومع ذلك، لا يزال يتعين التحقيق في العديد من القضايا ذات الصلة، بما في ذلك تحسين تقدير أحجام الجليد على المستويات المحلية، وإجراء تقييمات مفصلة للأهمية الهيدرولوجية لمختلف مكونات الغلاف الجليدي في أحواض أنهار الأنديز.

AbstractDeclines in terrestrial water storage (TWS) exacerbate regional water scarcity and global sea level rise. Increasing evidence has shown that recent TWS declines are substantial in ecologically fragile drylands, but the mechanism remains unclear. Here, by synergizing satellite observations and model simulations, we quantitatively attribute TWS trends during 2002–2016 in major climate zones to three mechanistic drivers: climate variability, climate change, and direct human activities. We reveal that climate variability had transitory and limited impacts (<20%), whereas warming‐induced glacier loss and direct human activities dominate the TWS loss in humid regions (∼103%) and drylands (∼64%), respectively. In non‐glacierized humid areas, climate variability generated regional water gains that offset synchronous TWS declines. Yet in drylands, TWS losses are enduring and more widespread with direct human activities, particularly unsustainable groundwater abstraction. Our findings highlight the substantive human footprints on the already vulnerable arid regions and an imperative need for improved dryland water conservation.

AbstractMost glaciological studies in Argentina have focused on the large outlet glaciers of the Southern Patagonia Icefield (SPI); the numerous smaller neighboring glaciers have received significantly less attention. We present an inventory of 248 medium- to small-size glaciers (0.01–25 km2) adjacent to the northeast margin of the SPI, describe their change over the period 1979–2005 and assess local and regional climatic variations in an attempt to explain the observed glacier changes. Based on an ASTER mosaic from 20 February 2005 and the ASTER Global Digital Elevation Model, we identified a total glacier area of 187.2 ± 7.4 km2 between 600 and 2870 m a.s.l. Glaciers are largely debris-free and are concentrated in the western, more humid sector adjacent to the SPI. Using a 20 March 1979 US military intelligence Hexagon KH-9 satellite photograph, we measured a total areal reduction of ∼33.7 km2 (15.2%) between 1979 and 2005. Ablation season temperatures from the study area have followed a regional warming trend that could partly explain the observed glacier shrinkage. Annual precipitation estimates show a gradual decrease between 1979 and 2002 that may also have contributed to the ice mass loss.

Monitoring the evolution of polar glaciers, ice caps and ice streams is of utmost importance because they constitute a good indicator of global climate change and contribute significantly to ongoing sea level rise. Accurate topographic surveys are particularly relevant as they reflect the geometric evolution of ice masses. Unfortunately, the precision and/or spatial coverage of current satellite missions (radar altimetry, ICESat) or field surveys are generally insufficient. Improving our knowledge of the topography of Polar Regions is the goal of the SPIRIT (SPOT 5 stereoscopic survey of Polar Ice: Reference Images and Topographies) international polar year (IPY) project. SPIRIT will allow (1) the acquisition of a large archive of SPOT 5 stereoscopic images covering most polar ice masses and, (2) the delivery of digital terrain models (DTM) to the scientific community. Here, we present the architecture of this project and the coverage achieved over northern and southern polar areas during the first year of IPY (July 2007 to April 2008). We also provide the first accuracy assessments of the SPIRIT DTMs. Over Jakobshavn Isbrae (West Greenland), SPIRIT elevations are within ± 6 m of ICESat elevations for 90% of the data. Some comparisons with ICESat profiles over Devon ice cap (Canada), St Elias Mountains (Alaska) and west Svalbard confirm the good overall quality of the SPIRIT DTMs although large errors are observed in the flat accumulation area of Devon ice cap. We then demonstrate the potential of SPIRIT DTMs for mapping glacier elevation changes. The comparison of summer-2007 SPIRIT DTMs with October-2003 ICESat profiles shows that the thinning of Jakobshavn Isbrae (by 30 to 40 m in 4 years) is restricted to the fast glacier trunk. The thinning of the coastal part of the ice stream (by over 100 m) and the retreat of its calving front (by up to 10 km) are clearly depicted by comparing the SPIRIT DTM to an ASTER April-2003 DTM.