Abstract
Knowledge about the long-term response of High Mountain Asian glaciers to climatic variations is paramount because of their important role in sustaining Asian river flow. Here, a ...satellite-based time series of glacier mass balance for seven climatically different regions across High Mountain Asia since the 1960s shows that glacier mass loss rates have persistently increased at most sites. Regional glacier mass budgets ranged from −0.40 ± 0.07 m w.e.a
−1
in Central and Northern Tien Shan to −0.06 ± 0.07 m w.e.a
−1
in Eastern Pamir, with considerable temporal and spatial variability. Highest rates of mass loss occurred in Central Himalaya and Northern Tien Shan after 2015 and even in regions where glaciers were previously in balance with climate, such as Eastern Pamir, mass losses prevailed in recent years. An increase in summer temperature explains the long-term trend in mass loss and now appears to drive mass loss even in regions formerly sensitive to both temperature and precipitation.
We report on a glacier inventory for the Canadian Cordillera south of 60°N, across the two western provinces of British Columbia and Alberta, containing ~
30,000
km
2 of glacierized terrain. Our ...semi-automated method extracted glacier extents from Landsat Thematic Mapper (TM) scenes for 2005 and 2000 using a band ratio (TM3/TM5). We compared these extents with glacier cover for the mid-1980s from high-altitude, aerial photography for British Columbia and from Landsat TM imagery for Alberta. A 25
m digital elevation model (DEM) helped to identify debris-covered ice and to split the glaciers into their respective drainage basins. The estimated mapping errors are 3–4% and arise primarily from seasonal snow cover. Glaciers in British Columbia and Alberta respectively lost −
10.8
±
3.8% and −
25.4%
±
4.1% of their area over the period 1985–2005. The region-wide annual shrinkage rate of −
0.55% a
−
1
is comparable to rates reported for other mountain ranges in the late twentieth century. Least glacierized mountain ranges with smaller glaciers lost the largest fraction of ice cover: the highest relative ice loss in British Columbia (−
24.0
±
4.6%) occurred in the northern Interior Ranges, while glaciers in the northern Coast Mountains declined least (−
7.7
±
3.4%).
Atmospheric rivers (ARs) often trigger extreme precipitation events in British Columbia (BC), Canada. Here we analyze how well the autumn AR events with the highest probability for extreme ...precipitation over BC, henceforth called AR‐extreme events, are simulated in five Coupled Model Intercomparison Project Phase 5 (CMIP5) global climate models (GCMs) and how these AR‐extreme events are projected to change by the end of the century. We examine the daily synoptic patterns of integrated water vapor transport (IVT) over the Pacific Ocean that favor the formation of AR‐extreme events. Our analysis and comparison with AR‐extreme events in four reanalysis products for the period 1979–2010 reveal that the GCMs more successfully resolve their seasonality and interannual variability than their frequencies and amount of precipitation brought to BC. For the CMIP5 scenario's Representative Concentration Pathway (RCP) 4.5 and RCP8.5, the frequency of AR‐extreme events will increase for the period 2070–2100 with the largest increase in December. All models project an increase in total precipitation over BC, due to the increase in frequency and intensity of the AR‐extreme events; however, the dominant factor is the increase in frequency, especially of those events with precipitation exceeding 20 mmd−1. The path of the ARs during the AR‐extreme events is projected to move northward, bringing stronger IVT and more precipitation to the north coast of BC, while the south coast may become drier than at the present day. The shift in the ARs is driven by the northward shift in the Aleutian Low pressure system, especially in RCP8.5.
Key Points
Landfalling atmospheric rivers are investigated using global climate models
Extreme atmospheric river events in BC will become more frequent and intense
Landfalling termini of atmospheric rivers are projected to move northward
Two catastrophic landslides occurred in quick succession on 13 and 16 May 2019, from the north face of Joffre Peak, Cerise Creek, southern Coast Mountains, British Columbia. With headscarps at 2560 m ...and 2690 m elevation, both began as rock avalanches, rapidly transforming into debris flows along middle Cerise Creek, and finally into debris floods affecting the fan. Beyond the fan margin, a flood surge on Cayoosh Creek reached bankfull and attenuated rapidly downstream; only fine sediment reached Duffey Lake. The toe of the main debris flow deposit reached 4 km from the headscarp, with a travel angle of 0.28, while the debris flood phase reached the fan margin 5.9 km downstream, with a travel angle of 0.22. Photogrammetry indicates the source volume of each event is 2–3 Mm
3
, with combined volume of 5 Mm
3
. Lidar differencing, used to assess deposit volume, yielded a similar total result, although error in the depth estimate introduced large volume error masking the expected increase due to dilation and entrainment. The average velocity of the rock avalanche-debris flow phases, from seismic analysis, was ~ 25–30 m/s, and the velocity of the 16 May debris flood on the upper fan, from super-elevation and boulder sizes, was 5–10 m/s. The volume of debris deposited on the fan was ~ 10
4
m
3
, 2 orders of magnitude less than the avalanche/debris flow phases. Progressive glacier retreat and permafrost degradation were likely the conditioning factors; precursor rockfall activity was noted at least ~6 months previous; thus, the mountain was primed to fail. The 13 May landslide was apparently triggered by rapid snowmelt, with debuttressing triggering the 16 May event.
Reliable, long-term records of glacier mass change are invaluable to the glaciological and climate-change communities and used to assess the importance of glacier wastage on streamflow. Here we ...evaluate the in-situ observations of glacier mass change for Place (1982–2020) and Peyto glaciers (1983–2020) in western Canada. We use geodetic mass balance to calibrate a physically-based mass-balance model coupled with an ice dynamics routine. We find large discrepancies between the glaciological and geodetic records for the periods 1987–1993 (Place) and 2001–2006 (Peyto). Over the period of observations, the exclusion of ice dynamics in the model increased simulated cumulative mass change by ~10.6 (24%) and 7.1 (21%) m w.e. for Place and Peyto glacier, respectively. Cumulative mass loss using geodetic, modelled and glaciological approaches are respectively − 30.5 ± 4.5, − 32.0 ± 3.6, − 29.7 ± 3.6 m w.e. for Peyto Glacier (1982–2017) and − 45.9 ± 5.2, − 43.1 ± 3.1, − 38.4 ± 5.1 m w.e. for Place Glacier (1981–2019). Based on discrepancies noted in the mass-balance records for certain decades (e.g. 1990s), we caution the community if these data are to be used for hydrological model development.
Several global datasets of glacier thickness exist, but the number of observations from western Canada are sparse and spatially biased. To supplement these limited observations, we measured ice ...thickness with ice penetrating radar on five glaciers in the Columbia Mountains, Canada. Our radar surveys, when combined with previous surveys for two glaciers in the Rocky Mountains, total 182 km of transects that represent 34 672 point measurements of ice thickness. Our measurements are, on average, 38% thicker than previous surface inversion model estimates of glacier thickness. Using our measurements within a cross-validation scheme, we model ice thickness with the Open Global Glacier Model (OGGM) driven with recent observations of surface mass balance and glacier elevation. We calibrated OGGM ice thickness by optimizing the ice creep parameter in the model. The optimized OGGM yields an ice volume for Columbia Basin of 122.5 ± 22.4 km3 for the year 2000, which is 23% greater than the range of previous estimates. At current rates of glacier mass loss for this region, glaciers would disappear from the basin in about 65–80 years. Disappearance of these glaciers will negatively affect the basin's surface hydrology, freshwater availability and aquatic ecosystems.
Seasonal measurements of glacier mass balance provide
insight into the relation between climate forcing and glacier change. To
evaluate the feasibility of using remotely sensed methods to assess ...seasonal
balance, we completed tandem airborne laser scanning (ALS) surveys and
field-based glaciological measurements over a 4-year period for six
alpine glaciers that lie in the Columbia and Rocky Mountains, near the
headwaters of the Columbia River, British Columbia, Canada. We calculated
annual geodetic balance using coregistered late summer digital elevation
models (DEMs) and distributed estimates of density based on surface
classification of ice, snow, and firn surfaces. Winter balance was derived
using coregistered late summer and spring DEMs, as well as density measurements
from regional snow survey observations and our glaciological measurements.
Geodetic summer balance was calculated as the difference between winter and
annual balance. Winter mass balance from our glaciological observations
averaged 1.95±0.09 m w.e. (meter water equivalent), 4 % larger than those derived from
geodetic surveys. Average glaciological summer and annual balance were 3 %
smaller and 3 % larger, respectively, than our geodetic estimates. We find
that distributing snow, firn, and ice density based on surface classification
has a greater influence on geodetic annual mass change than the density
values themselves. Our results demonstrate that accurate assessments of
seasonal mass change can be produced using ALS over a series of glaciers
spanning several mountain ranges. Such agreement over multiple seasons,
years, and glaciers demonstrates the ability of high-resolution geodetic
methods to increase the number of glaciers where seasonal mass balance can
be reliably estimated.
The mass-balance—elevation relation for a given glacier is required for many numerical models of ice flow. Direct measurements of this relation using remotely-sensed methods are complicated by ice ...dynamics, so observations are currently limited to glaciers where surface mass-balance measurements are routinely made. We test the viability of using the continuity equation to estimate annual surface mass balance between flux-gates in the absence of
in situ
measurements, on five glaciers in the Columbia Mountains of British Columbia, Canada. Repeat airborne laser scanning surveys of glacier surface elevation, ice penetrating radar surveys and publicly available maps of ice thickness are used to estimate changes in surface elevation and ice flux. We evaluate this approach by comparing modeled to observed mass balance. Modeled mass-balance gradients well-approximate those obtained from direct measurement of surface mass balance, with a mean difference of +6.6
±
4%. Regressing modeled mass balance, equilibrium line altitudes are on average 15 m higher than satellite-observations of the transient snow line. Estimates of mass balance over flux bins compare less favorably than the gradients. Average mean error (+0.03
±
0.07 m w.e.) between observed and modeled mass balance over flux bins is relatively small, yet mean absolute error (0.55
±
0.18 m w.e.) and average modeled mass-balance uncertainty (0.57 m w.e.) are large. Mass conservation, assessed with glaciological data, is respected (when estimates are within 1σ uncertainties) for 84% of flux bins representing 86% of total glacier area. Uncertainty on ice velocity, especially for areas where surface velocity is low (<10 m a
−1
) contributes the greatest error in estimating ice flux. We find that using modeled ice thicknesses yields comparable modeled mass-balance gradients relative to using observations of ice thickness, but we caution against over-interpreting individual flux-bin mass balances due to large mass-balance residuals. Given the performance of modeled ice thickness and the increasing availability of ice velocity and surface topography data, we suggest that similar efforts to produce mass-balance gradients using modern high-resolution datasets are feasible on larger scales.
Abstract
Finely resolved geodetic data provide an opportunity to assess the extent and morphology of crevasses and their change over time. Crevasses have the potential to bias geodetic measurements ...of elevation and mass change unless they are properly accounted for. We developed a framework that automatically maps and extracts crevasse geometry and masks them where they interfere with surface mass-balance assessment. Our study examines airborne light detection and ranging digital elevation models (LiDAR DEMs) from Haig Glacier, which is experiencing a transient response in its crevassed upper regions as the glacier thins, using a self-organizing map algorithm. This method successfully extracts and characterizes ~1000 crevasses, with an overall accuracy of 94%. The resulting map provides insight into stress and flow conditions. The crevasse mask also enables refined geodetic estimates of summer mass balance. From differencing of September and April LiDAR DEMs, the raw LiDAR DEM gives a 9% overestimate in the magnitude of glacier thinning over the summer: −5.48 m compared with a mean elevation change of −5.02 m when crevasses are masked out. Without identification and removal of crevasses, the LiDAR-derived summer mass balance therefore has a negative bias relative to the glaciological surface mass balance.
This study focused on the effects of glacier wastage on streamflow in the Canadian portion of the Columbia River headwaters over the period 1977 to 2017. Between 1985 and 2013, glacier coverage ...decreased by up to 2% of catchment area for the 35 study catchments. The mean wastage flux contribution to streamflow had a positive relation with fractional glacier coverage and an inverse relation with catchment water yield. Glacier mass change estimates suggest that wastage flux contributions declined between 1985–1999 and 2000–2018, but the estimates are subject to substantial uncertainty. Annual wastage flux contributions over a four-year period for two study catchments ranged from 8 to 13% of annual water yield for a catchment with 17% glacier cover, with glaciers extending below treeline, and 9–19% for a smaller alpine catchment with 57% glacier cover. After accounting statistically for climatic forcing and non-glacial contributions to streamflow, August runoff from glacierized catchments decreased through time at a rate that was linearly related to loss of glacier cover. The analyses suggest that glacier-melt contributions to August runoff have already have passed peak water, and that these reductions have exacerbated a regional climate-driven trend to decreased August streamflow contributions from unglacierized areas.
PDF
