Quantifying the contribution of glacier runoff to streamflow in the upper Columbia River Basin, Canada

Glacier melt provides important contributions to streamflow in many mountainous regions. Hydrologic model calibration in glacier-fed catchments is difficult because errors in modelling snow accumulation can be offset by compensating errors in glacier melt. This problem is particularly severe in catchments with modest glacier cover, where goodness-of-fit statistics such as the Nash-Sutcliffe model efficiency may not be highly sensitive to the streamflow variance associated with glacier melt. While glacier mass balance measurements can be used to aid model calibration, they are absent for most catchments. We introduce the use of glacier volume change determined from repeated glacier mapping in a guided GLUE (generalized likelihood uncertainty estimation) procedure to calibrate a hydrologic model. This approach is applied to the Mica basin in the Canadian portion of the Columbia River Basin using the HBV-EC hydrologic model. Use of glacier volume change in the calibration procedure effectively reduced parameter uncertainty and helped to ensure that the model was accurately predicting glacier mass balance as well as streamflow. The seasonal and interannual variations in glacier melt contributions were assessed by running the calibrated model with historic glacier cover and also after converting all glacierized areas to alpine land cover in the model setup. Sensitivity of modelled streamflow to historic changes in glacier cover and to projected glacier changes for a climate warming scenario was assessed by comparing simulations using static glacier cover to simulations that accommodated dynamic changes in glacier area. Although glaciers in the Mica basin only cover 5% of the watershed, glacier ice melt contributes up to 25% and 35% of streamflow in August and September, respectively. The mean annual contribution of ice melt to total streamflow varied between 3 and 9% and averaged 6%. Glacier ice melt is particularly important during warm, dry summers following winters with low snow accumulation and early snowpack depletion. Although the sensitivity of streamflow to historic glacier area changes is small and within parameter uncertainties, our results suggest that glacier area changes have to be accounted for in future projections of late summer streamflow. Our approach provides an effective and widely applicable method to calibrate hydrologic models in glacier fed catchments, as well as to quantify the magnitude and timing of glacier melt contributions to streamflow

A multi-season investigation of glacier surface roughness lengths through in situ and remote observation

The roughness length values for momentum, temperature, and water vapour are key inputs to the bulk aerodynamic method for estimating turbulent heat flux. Measurements of site-specific roughness length are rare for glacier surfaces, and substantial uncertainty remains in the values and ratios commonly assumed when parameterising turbulence. Over three melt seasons, eddy covariance observations were implemented to derive the momentum and scalar roughness lengths at several locations on two mid-latitude mountain glaciers. In addition, two techniques were developed in this study for the remote estimation of momentum roughness length, utilising lidar-derived digital elevation models with a 1×1&thinsp;m resolution. Seasonal mean momentum roughness length values derived from eddy covariance observations at each location ranged from 0.7 to 4.5&thinsp;mm for ice surfaces and 0.5 to 2.4&thinsp;mm for snow surfaces. From one season to the next, mean momentum roughness length values over ice remained relatively consistent at a given location (0–1&thinsp;mm difference between seasonal mean values), while within a season, temporal variability in momentum roughness length over melting snow was found to be substantial (&gt; an order of magnitude). The two remote techniques were able to differentiate between ice and snow cover and return momentum roughness lengths that were within 1–2&thinsp;mm (≪ an order of magnitude) of the in situ eddy covariance values. Changes in wind direction affected the magnitude of the momentum roughness length due to the anisotropic nature of features on a melting glacier surface. Persistence in downslope wind direction on the glacier surfaces, however, reduced the influence of this variability. Scalar roughness length values showed considerable variation (up to 2.5 orders of magnitude) between locations and seasons and no evidence of a constant ratio with momentum roughness length or each other. Of the tested estimation methods, the Andreas (1987) surface renewal model returned scalar roughness lengths closest to those derived from eddy covariance observations. Combining this scalar method with the remote techniques developed here for estimating momentum roughness length may facilitate the distributed parameterisation of turbulent heat flux over glacier surfaces without in situ measurements.</p

Kinematic Analysis of the 2020 Elliot Creek Landslide, British Columbia, Using Remote Sensing Data

The 2020 Elliot Creek landslide-tsunami-flood cascade originated from an 18.3&nbsp;Mm3 rock slope failure in quartz diorite bedrock in a valley undergoing rapid glacial retreat. We used airborne LiDAR and optical imagery to characterize the slope and its surroundings. Using the LiDAR, we determined that two rockslides (2020 and an older undated one) occurred on this slope and shared a common basal rupture surface. We mapped two main sets of lineaments that represent structures that controlled the orientation of the lateral and rear release surfaces. Analysis of the topographic profile indicates a wedge-shaped failure block and a stepped rupture surface. Further topographic profile analysis indicates the possibility of a structurally controlled geomorphic step in the valley that corresponds with a change in the orientation of the valley. The rapid retreat of the West Grenville Glacier and the positions of the rupture surfaces suggest glacial retreat played a role in the landslides

High Mountain Asian glacier response to climate revealed by multi-temporal satellite observations since the 1960s

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 \ub1 0.07 m w.e.a−1 in Central and Northern Tien Shan to −0.06 \ub1 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

Four North American glaciers advanced past their modern positions thousands of years apart in the Holocene

There is unambiguous evidence that glaciers have retreated from their 19th century positions, but it is less clear how far glaciers have retreated relative to their long-term Holocene fluctuations. Glaciers in western North America are thought to have advanced from minimum positions in the Early Holocene to maximum positions in the Late Holocene. We assess when four North American glaciers, located between 38–60∘ N, were larger or smaller than their modern (2018–2020 CE) positions during the Holocene. We measured 26 paired cosmogenic in situ 14C and 10Be concentrations in recently exposed proglacial bedrock and applied a Monte Carlo forward model to reconstruct plausible bedrock exposure–burial histories. We find that these glaciers advanced past their modern positions thousands of years apart in the Holocene: a glacier in the Juneau Icefield (BC, Canada) at ∼2 ka, Kokanee Glacier (BC, Canada) at ∼6 ka, and Mammoth Glacier (WY, USA) at ∼1 ka; the fourth glacier, Conness Glacier (CA, USA), was likely larger than its modern position for the duration of the Holocene until present. The disparate Holocene exposure–burial histories are at odds with expectations of similar glacier histories given the presumed shared climate forcings of decreasing Northern Hemisphere summer insolation through the Holocene followed by global greenhouse gas forcing in the industrial era. We hypothesize that the range in histories is the result of unequal amounts of modern retreat relative to each glacier's Holocene maximum position, rather than asynchronous Holocene advance histories. We explore the influence of glacier hypsometry and response time on glacier retreat in the industrial era as a potential cause of the non-uniform burial durations. We also report mean abrasion rates at three of the four glaciers: Juneau Icefield Glacier (0.3±0.3 mm yr−1), Kokanee Glacier (0.04±0.03 mm yr−1), and Mammoth Glacier (0.2±0.2 mm yr−1).</p

The 28 November 2020 Landslide, Tsunami, and Outburst Flood – A Hazard Cascade Associated With Rapid Deglaciation at Elliot Creek, British Columbia, Canada

We describe and model the evolution of a recent landslide, tsunami, outburst flood, and sediment plume in the southern Coast Mountains, British Columbia, Canada. On November 28, 2020, about 18 million m3 of rock descended 1,000&nbsp;m from a steep valley wall and traveled across the toe of a glacier before entering a 0.6&nbsp;km2 glacier lake and producing &gt;100-m high run-up. Water overtopped the lake outlet and scoured a 10-km long channel before depositing debris on a 2-km2 fan below the lake outlet. Floodwater, organic debris, and fine sediment entered a fjord where it produced a 60+km long sediment plume and altered turbidity, water temperature, and water chemistry for weeks. The outburst flood destroyed forest and salmon spawning habitat. Physically based models of the landslide, tsunami, and flood provide real-time simulations of the event and can improve understanding of similar hazard cascades and the risk they pose

Contribution of Alaskan glaciers to sea level rise derived from satellite imagery

International audienceOver the last 50 years, retreating glaciers and ice caps (GIC) contributed 0.5 mm/yr to sea level rises (SLR), and one third is believed to originate from ice masses bordering the Gulf of Alaska. However, these estimates of ice wastage in Alaska are based on methods that measure a limited number of glaciers and extrapolate the results to estimate ice loss for the many thousands of others. How these methods capture the complex pattern of decadal elevation changes at the scale of individual glacier and mountain range is unclear. Here, combining a comprehensive glacier inventory with elevation changes derived from sequential digital elevation models (DEMs), we found that, between 1962 and 2006, Alaskan glaciers lost 41.9 ± 8.6 km**3/yr water equivalent (w.e.) and contributed 0.12±0.02 mm/yr to SLR. Our ice loss is 34% lower than previous estimates. Reasons for our lower values include the higher spatial resolution of our glacier inventory and the reduction of ice thinning under debris and at the glacier margins which were not resolved in earlier work. Estimates of mass loss from GIC in other mountain regions could be subject to similar revisions

Prevalence and molecular characterization of Glucose-6-Phosphate dehydrogenase deficient variants among the Kurdish population of Northern Iraq

<p>Abstract</p> <p>Background</p> <p>Glucose-6-Phosphate dehydrogenase (G6PD) is a key enzyme of the pentose monophosphate pathway, and its deficiency is the most common inherited enzymopathy worldwide. G6PD deficiency is common among Iraqis, including those of the Kurdish ethnic group, however no study of significance has ever addressed the molecular basis of this disorder in this population. The aim of this study is to determine the prevalence of this enzymopathy and its molecular basis among Iraqi Kurds.</p> <p>Methods</p> <p>A total of 580 healthy male Kurdish Iraqis randomly selected from a main regional premarital screening center in Northern Iraq were screened for G6PD deficiency using methemoglobin reduction test. The results were confirmed by quantitative enzyme assay for the cases that showed G6PD deficiency. DNA analysis was performed on 115 G6PD deficient subjects, 50 from the premarital screening group and 65 unrelated Kurdish male patients with documented acute hemolytic episodes due to G6PD deficiency. Analysis was performed using polymerase chain reaction/restriction fragment length polymorphism for five deficient molecular variants, namely G6PD Mediterranean (563 C→T), G6PD Chatham (1003 G→A), G6PD A- (202 G→A), G6PD Aures (143 T→C) and G6PD Cosenza (1376 G→C), as well as the silent 1311 (C→T) mutation.</p> <p>Results</p> <p>Among 580 random Iraqi male Kurds, 63 (10.9%) had documented G6PD deficiency. Molecular studies performed on a total of 115 G6PD deficient males revealed that 101 (87.8%) had the G6PD Mediterranean variant and 10 (8.7%) had the G6PD Chatham variant. No cases of G6PD A-, G6PD Aures or G6PD Cosenza were identified, leaving 4 cases (3.5%) uncharacterized. Further molecular screening revealed that the silent mutation 1311 was present in 93/95 of the Mediterranean and 1/10 of the Chatham cases.</p> <p>Conclusions</p> <p>The current study revealed a high prevalence of G6PD deficiency among Iraqi Kurdish population of Northern Iraq with most cases being due to the G6PD Mediterranean and Chatham variants. These results are similar to those reported from neighboring Iran and Turkey and to lesser extent other Mediterranean countries.</p

Molecular characterization of glucose-6-phosphate dehydrogenase deficient variants in Baghdad city - Iraq

Background: Although G6PD deficiency is the most common genetically determined blood disorder among Iraqis, its molecular basis has only recently been studied among the Kurds in North Iraq, while studies focusing on Arabs in other parts of Iraq are still absent. Methods: A total of 1810 apparently healthy adult male blood donors were randomly recruited from the national blood transfusion center in Baghdad. They were classified into G6PD deficient and non-deficient individuals based on the results of methemoglobin reduction test (MHRT), with confirmation of deficiency by subsequent enzyme assays. DNA from deficient individuals was studied using a polymerase chain reaction-Restriction fragment length polymorphism (PCR-RFLP) for four deficient molecular variants, namely G6PD Mediterranean (563 C®T), Chatham (1003 G®A), A- (202 G®A) and Aures (143 T®C). A subset of those with the Mediterranean variant, were further investigated for the 1311 (C®T) silent mutation. Results: G6PD deficiency was detected in 109 of the 1810 screened male individuals (6.0%). Among 101 G6PD deficient males molecularly studied, the Mediterranean mutation was detected in 75 cases (74.3%), G6PD Chatham in 5 cases (5.0%), G6PD A- in two cases (2.0%), and G6PD Aures in none. The 1311 silent mutation was detected in 48 out of the 51 G6PD deficient males with the Mediterranean variant studied (94.1%). Conclusions: Three polymorphic variants namely: the Mediterranean, Chatham and A-, constituted more than 80% of G6PD deficient variants among males in Baghdad. Iraq. This observation is to some extent comparable to othe

The 28 November 2020 landslide, tsunami, and outburst flood – a hazard cascade associated with rapid deglaciation at Elliot Creek, British Columbia, Canada

We describe and model the evolution of a recent landslide, tsunami, outburst flood, and sediment plume in the southern Coast Mountains, British Columbia, Canada. On November 28, 2020, about 18 million m3 of rock descended 1,000 m from a steep valley wall and traveled across the toe of a glacier before entering a 0.6 km2 glacier lake and producing >100-m high run-up. Water overtopped the lake outlet and scoured a 10-km long channel before depositing debris on a 2-km2 fan below the lake outlet. Floodwater, organic debris, and fine sediment entered a fjord where it produced a 60+km long sediment plume and altered turbidity, water temperature, and water chemistry for weeks. The outburst flood destroyed forest and salmon spawning habitat. Physically based models of the landslide, tsunami, and flood provide real-time simulations of the event and can improve understanding of similar hazard cascades and the risk they pose