2023 |
Berthier, E., Floriciou, D., Gardner, A., Gourmelen, N., Jakob, L., Paul, F., et al. (2023). Measuring Glacier Mass Changes From Space-A Review. Reports On Progress In Physics, 868(3).
Abstract: Glaciers Distinct From The Greenland And Antarctic Ice Sheets Are Currently Losing Mass Rapidly With Direct And Severe Impacts On The Habitability Of Some Regions On Earth As Glacier Meltwater Contributes To Sea-Level Rise And Alters Regional Water Resources In Arid Regions. In This Review, We Present The Different Techniques Developed During The Last Two Decades To Measure Glacier Mass Change From Space: Digital Elevation Model (Dem) Differencing From Stereo-Imagery And Synthetic Aperture Radar Interferometry, Laser And Radar Altimetry And Space Gravimetry. We Illustrate Their Respective Strengths And Weaknesses To Survey The Mass Change Of A Large Arctic Ice Body, The Vatnajokull Ice Cap (Iceland) And For The Steep Glaciers Of The Everest Area (Himalaya). For Entire Regions, Mass Change Estimates Sometimes Disagree When A Similar Technique Is Applied By Different Research Groups. At Global Scale, These Discrepancies Result In Mass Change Estimates Varying By 20%-30%. Our Review Confirms The Need For More Thorough Inter-Comparison Studies To Understand The Origin Of These Differences And To Better Constrain Regional To Global Glacier Mass Changes And, Ultimately, Past And Future Glacier Contribution To Sea-Level Rise.
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Brun, F., King, O., Reveillet, M., Amory, C., Planchot, A., Berthier, E., et al. (2023). Everest South Col Glacier Did Not Thin During The Period 1984-2017. Cryosphere, 171(8), 3251–3268.
Abstract: The South Col Glacier Is A Small Body Of Ice And Snow (Approx. 0.2 Km(2)) Located At The Very High Elevation Of 8000Ma.S.L. (Above Sea Level) On The Southern Ridge Of Mt. Everest. A Recent Study By Potocki Et Al. (2022) Proposed That South Col Glacier Is Rapidly Losing Mass. This Is In Contradiction To Our Comparison Of Two Digital Elevation Models Derived From Aerial Photographs Taken In December 1984 And A Stereo Pleiades Satellite Acquisition From March 2017, From Which We Estimate A Mean Elevation Change Of 0.01 +/- 0.05M A(-1). To Reconcile These Results, We Investigate Some Aspects Of The Surface Energy And Mass Balance Of South Col Glacier. From Satellite Images And A Simple Model Of Snow Compaction And Erosion, We Show That Wind Erosion Has A Major Impact On The Surface Mass Balance Due To The Strong Seasonality In Precipitation And Wind And That It Cannot Be Neglected. Additionally, We Show That The Melt Amount Predicted By A Surface Energy And Mass Balance Model Is Very Sensitive To The Model Structure And Implementation. Contrary To Previous Findings, Melt Is Likely Not A Dominant Ablation Process On This Glacier, Which Remains Mostly Snow-Covered During The Monsoon.
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Guo, L., Li, J., Dehecq, A., Li, Z., Li, X., & Zhu, J. (2023). A New Inventory Of High Mountain Asia Surging Glaciers Derived From Multiple Elevation Datasets Since The 1970S. Earth System Science Data, , 284122–286122.
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Knuth, F., Shean, D., Bhushan, S., Schwat, E., Alexandrov, O., Mcneil, C., et al. (2023). Historical Structure From Motion (Hsfm): Automated Processing Of Historical Aerial Photographs For Long-Term Topographic Change Analysis. Remote Sensing Of Environment, 2852.
Abstract: Precisely Measuring The Earth'S Changing Surface On Decadal To Centennial Time Scales Is Critical For Many Science And Engineering Applications, Yet Long-Term Records Of Quantitative Landscape Change Are Often Temporally And Geographically Sparse. Archives Of Scanned Historical Aerial Photographs Provide An Opportunity To Augment These Records With Accurate Elevation Measurements That Capture The Historical State Of The Earth Surface. Structure From Motion (Sfm) Photogrammetry Workflows Produce High-Quality Digital Elevation Models (Dems) And Orthoimage Mosaics From These Historical Images, But Time-Intensive Tasks Like Manual Image Preprocessing (E.G., Fiducial Marker Identification) And Ground Control Point (Gcp) Selection Impede Processing At Scale. We Developed An Automated Method To Process Historical Images And Generate Self-Consistent Time Series Of High-Resolution (0.5-2 M) Dems And Orthomosaics, Without Manual Gcp Selection. The Method Relies On Sfm To Correct Camera Interior And Exterior Orientation And A Robust Multi-Stage Co-Registration Approach Using Modern Reference Terrain Datasets For Geolocation Refinement. We Demonstrate The Method Using Scanned Images From The North American Glacier Aerial Photography (Nagap) Archive Collected Between 1967 And 1997. We Present Results For Two Sites With Variable Photo Acquisition Geometry And Overlap – Mount Baker And South Cascade Glacier In Washington State, Usa. The Automated Method Corrects Initial Camera Position Errors Of Several Kilometers And Produces Accurately Georeferenced, High-Resolution Dems And Orthoimages, Regardless Of Camera Configuration, Acquisition Geometry, Terrain Characteristics, And Reference Dem Properties. The Average Rms Reprojection Error Following Bundle Adjustment Optimization Was 0.67 Px (0.15 M) For The 261 Images Contributing To 10 Final Dem Mosaics Between 1970 And 1992 At Mount Baker, And 0.65 Px (0.13 M) For The 243 Images Contributing To 18 Individual Dems Between 1967 And 1997 At South Cascade Glacier. The Relative Accuracy Of Elevation Values In The Historical Time Series Stacks Was 0.68 M At Mount Baker And 0.37 M At South Cascade Glacier. Our Products Have Reduced Systematic Error And Improved Accuracy Compared To Dem Products Generated Using Sfm With Manual Gcp Selection. Final Elevation Change Measurement Precision Was Similar To 0.7-1.0 M Over A 30-Year Period, Enabling The Study Of Processes With Rates As Low As Similar To 1-3 Cm/Yr. Our Results Demonstrate The Potential Of This Scalable Method To Rapidly Process Archives Of Historical Imagery And Deliver New Quantitative Insights On Long-Term Geodetic Change And Earth Surface Processes.
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2022 |
Hugonnet, R., Brun, F., Berthier, E., Dehecq, A., Mannerfelt, E., Eckert, N., et al. (2022). Uncertainty Analysis Of Digital Elevation Models By Spatial Inference From Stable Terrain. Ieee Journal Of Selected Topics In Applied Earth Observations And Remote Sensing, 151, 6456–6472.
Abstract: The Monitoring Of Earth'S And Planetary Surface Elevations At Larger And Finer Scales Is Rapidly Progressing Through The Increasing Availability And Resolution Of Digital Elevation Models (Dems). Surface Elevation Observations Are Being Used Across An Expanding Range Of Fields To Study Topographical Attributes And Their Changes Over Time, Notably In Glaciology, Hydrology, Volcanology, Seismology, Forestry, And Geomorphology. However, Dems Frequently Contain Large-Scale Instrument Noise And Varying Vertical Precision That Lead To Complex Patterns Of Errors. Here, We Present A Validated Statistical Workflow To Estimate, Model, And Propagate Uncertainties In Dems. We Review The State-Of-The-Art Of Dem Accuracy And Precision Analyses, And Define A Conceptual Framework To Consistently Address Those. We Show How To Characterize Dem Precision By Quantifying The Heteroscedasticity Of Elevation Measurements, I.E., Varying Vertical Precision With Terrain- Or Sensor-Dependent Variables, And The Spatial Correlation Of Errors That Can Occur Across Multiple Spatial Scales. With The Increasing Availability Of High-Precision Observations, Our Workflow Based On Independent Elevation Data Acquired On Stable Terrain Can Be Applied Almost Anywhere On Earth. We Illustrate How To Propagate Uncertainties For Both Pixel-Scale And Spatial Elevation Derivatives, Using Terrain Slope And Glacier Volume Changes As Examples. We Find That Uncertainties In Dems Are Largely Underestimated In The Literature, And Advocate That New Metrics Of Dem Precision Are Essential To Ensure The Reliability Of Future Land Elevation Assessments.
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Jouberton, A., Shaw, T., Miles, E., Mccarthy, M., Fugger, S., Ren, S., et al. (2022). Warming-Induced Monsoon Precipitation Phase Change Intensifies Glacier Mass Loss In The Southeastern Tibetan Plateau. Proceedings Of The National Academy Of Sciences Of The United States Of America, .
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Jouberton, A., Shaw, T., Miles, E., Mccarthy, M., Fugger, S., Ren, S., et al. (2022). Warming-Induced Monsoon Precipitation Phase Change Intensifies Glacier Mass Loss In The Southeastern Tibetan Plateau. Proceedings Of The National Academy Of Sciences Of The United States Of America, 1191(373).
Abstract: Glaciers Are Key Components Of The Mountain Water Towers Of Asia And Are Vital For Downstream Domestic, Agricultural, And Industrial Uses. The Glacier Mass Loss Rate Over The Southeastern Tibetan Plateau Is Among The Highest In Asia And Has Accelerated In Recent Decades. This Acceleration Has Been Attributed To Increased Warming, But The Mechanisms Behind These Glaciers' High Sensitivity To Warming Remain Unclear, While The Influence Of Changes In Precipitation Over The Past Decades Is Poorly Quantified. Here, We Reconstruct Glacier Mass Changes And Catchment Runoff Since 1975 At A Benchmark Glacier, Parlung No. 4, To Shed Light On The Drivers Of Recent Mass Losses For The Monsoonal, Spring-Accumulation Glaciers Of The Tibetan Plateau. Our Modeling Demonstrates How A Temperature Increase (Mean Of 0.39 Degrees C Center Dot Dec(-1) Since 1990) Has Accelerated Mass Loss Rates By Altering Both The Ablation And Accumulation Regimes In A Complexmanner. The Majority Of The Post-2000 Mass Loss Occurred During Themonsoon Months, Caused By Simultaneous Decreases In The Solid Precipitation Ratio (From 0.70 To 0.56) And Precipitation Amount (-10%), Leading To Reduced Monsoon Accumulation (-26%). Higher Solid Precipitation In Spring (+18%) During The Last Two Decades Was Increasingly Important In Mitigating Glacier Mass Loss By Providing Mass To The Glacier And Protecting It From Melting In The Early Monsoon. With Bare Ice Exposed To Warmer Temperatures For Longer Periods, Icemelt And Catchment Discharge Have Unsustainably Intensified Since The Start Of The 21St Century, Raising Concerns For Long-Term Water Supply And Hazard Occurrence In The Region.
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Mannerfelt, E., Dehecq, A., Hugonnet, R., Hodel, E., Huss, M., Bauder, A., et al. (2022). Halving Of Swiss Glacier Volume Since 1931 Observed From Terrestrial Image Photogrammetry. Cryosphere, 161(8), 3249–3268.
Abstract: The Monitoring Of Glaciers In Switzerland Has A Long Tradition, Yet Glacier Changes During The 20Th Century Are Only Known Through Sparse Observations. Here, We Estimate A Halving Of Swiss Glacier Volumes Between 1931 And 2016 By Mapping Historical Glacier Elevation Changes At High Resolution. Our Analysis Relies On A Terrestrial Image Archive Known As Terra, Which Covers About 86 % Of The Swiss Glacierised Area With 21 703 Images Acquired During The Period 1916-1947 (With A Median Date Of 1931). We Developed A Semi-Automated Workflow To Generate Digital Elevation Models (Dems) From These Images, Resulting In A 45 % Total Glacier Coverage. Using The Geodetic Method, We Estimate A Swisswide Glacier Mass Balance Of -0.52 +/- 0.09 M W.E. A(-1) Between 1931 And 2016. This Equates To A 51.5 +/- 8.0 % Loss In Glacier Volume. We Find That Low-Elevation, High-Debriscover, And Gently Sloping Glacier Termini Are Conducive To Particularly High Mass Losses. In Addition To These Glacier-Specific, Quasi-Centennial Elevation Changes, We Present A New Inventory Of Glacier Outlines With Known Timestamps And Complete Attributes From Around 1931. The Fragmented Spatial Coverage And Temporal Heterogeneity Of The Terra Archive Are The Largest Sources Of Uncertainty In Our Glacier-Specific Estimates, Reaching Up To 0.50 M W.E. A(-1). We Suggest That The High-Resolution Mapping Of Historical Surface Elevations Could Also Unlock Great Potential For Research Fields Other Than Glaciology.
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Saks, T., Pohl, E., Machguth, H., Dehecq, A., Barandun, M., Kenzhebaev, R., et al. (2022). Glacier Runoff Variation Since 1981 in the Upper Naryn River Catchments, Central Tien Shan. Frontiers In Environmental Science, 9.
Abstract: Water resources in Central Asia strongly depend on glaciers, which in turn adjust their size in response to climate variations. We investigate glacier runoff in the period 1981-2019 in the upper Naryn basin, Kyrgyzstan. The basins contain more than 1,000 glaciers, which cover a total area of 776 km(2). We model the mass balance and runoff contribution of all glaciers with a simplified energy balance melt model and distributed accumulation model driven by ERA5 LAND re-analysis data for the time period of 1981-2019. The results are evaluated against discharge records, satellite-derived snow cover, stake readings from individual glaciers, and geodetic mass balances. Modelled glacier volume decreased by approximately 6.7 km(3) or 14%, and the majority of the mass loss took place from 1996 until 2019. The decreasing trend is the result of increasingly negative summer mass balances whereas winter mass balances show no substantial trend. Analysis of the discharge data suggests an increasing runoff for the past two decades, which is, however only partly reflected in an increase of glacier melt. Moreover, the strongest increase in discharge is observed in winter, suggesting either a prolonged melting period and/or increased groundwater discharge. The average runoff from the glacierized areas in summer months (June to August) constitutes approximately 23% of the total contributions to the basin's runoff. The results highlight the strong regional variability in glacier-climate interactions in Central Asia.
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Saks, T., Pohl, E., Machguth, H., Dehecq, A., Barandun, M., Kenzhebaev, R., et al. (2022). Glacier Runoff Variation Since 1981 In The Upper Naryn River Catchments, Central Tien Shan (Vol 9, 780466, 2022). Frontiers In Environmental Science, 101.
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2021 |
Wagnon, P., Brun, F., Khadka, A., Berthier, E., Shrestha, D., Vincent, C., et al. (2021). Reanalysing the 2007-19 glaciological mass-balance series of Mera Glacier, Nepal, Central Himalaya, using geodetic mass balance. Journal Of Glaciology, 67(261), 117–125.
Abstract: The 2007-19 glaciological mass-balance series of Mera Glacier in the Everest Region, East Nepal, is reanalysed using the geodetic mass balance assessed by differencing two DEMs obtained from Pleiades stereo-images acquired in November 2012 and in October 2018. The glaciological glacier-wide annual mass balance of Mera Glacier has to be systematically decreased by 0.11 m w.e. a(-1) to match the geodetic mass balance. We attribute part of the positive bias of the glaciological mass balance to an over-estimation of the accumulation above 5520 m a.s.l., likely due to a measurement network unable to capture its spatial variability. Over the period 2007-19, Mera Glacier has lost mass at a rate of -0.41 +/- 0.20 m w.e. a(-1), in general agreement with regional averages for the central Himalaya. We observe a succession of negative mass-balance years since 2013.
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2019 |
Dehecq, A., Gourmelen, N., Gardner, A., Brun, F., Goldberg, D., Nienow, P., et al. (2019). Twenty-first century glacier slowdown driven by mass loss in High Mountain Asia. Nature Geoscience, 12(1), 22–+.
Abstract: Glaciers in High Mountain Asia have experienced heterogeneous rates of loss since the 1970s. Yet, the associated changes in ice flow that lead to mass redistribution and modify the glacier sensitivity to climate are poorly constrained. Here we present observations of changes in ice flow for all glaciers in High Mountain Asia over the period 2000-2017, based on one million pairs of optical satellite images. Trend analysis reveals that in 9 of the 11 surveyed regions, glaciers show sustained slowdown concomitant with ice thinning. In contrast, the stable or thickening glaciers of the Karakoram and West Kunlun regions experience slightly accelerated glacier flow. Up to 94% of the variability in velocity change between regions can be explained by changes in gravitational driving stress, which in turn is largely controlled by changes in ice thickness. We conclude that, despite the complexities of individual glacier behaviour, decadal and regional changes in ice flow are largely insensitive to changes in conditions at the bed of the glacier and can be well estimated from ice thickness change and slope alone.
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Menounos, B., Hugonnet, R., Shean, D., Gardner, A., Howat, I., Berthier, E., et al. (2019). Heterogeneous Changes in Western North American Glaciers Linked to Decadal Variability in Zonal Wind Strength. Geophysical Research Letters, 46(1), 200–209.
Abstract: Western North American (WNA) glaciers outside of Alaska cover 14,384km(2) of mountainous terrain. No comprehensive analysis of recent mass change exists for this region. We generated over 15,000 multisensor digital elevation models from spaceborne optical imagery to provide an assessment of mass change for WNA over the period 2000-2018. These glaciers lost 11742gigatons (Gt) of mass, which accounts for up to 0.320.11mm of sea level rise over the full period of study. We observe a fourfold increase in mass loss rates between 2000-2009 [-2.93.1Gt yr(-1)] and 2009-2018 [-12.34.6Gt yr(-1)], and we attribute this change to a shift in regional meteorological conditions driven by the location and strength of upper level zonal wind. Our results document decadal-scale climate variability over WNA that will likely modulate glacier mass change in the future. Plain Language Summary Glaciers in western North America provide important thermal and flow buffering to streams when seasonal snowpack is depleted. We used spaceborne optical satellite imagery to produce thousands of digital elevation models to assess recent mass loss for glaciers in western North America outside of Alaska. Our analysis shows that glacier loss over the period 2009-2018 increased fourfold relative to the period 2000-2009. This mass change over the last 18years is partly explained by changes in atmospheric circulation. Our results can be used for future modeling studies to understand the fate of glaciers under future climate change scenarios.
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