Updates from Cambridge: PhD, new OA paper, new project

Evan Miles passes PhD viva

Research team member Evan Miles, based at the University of Cambridge, has recently passed his PhD viva and will now be Dr Miles!  His thesis, titled ‘Spatio-temporal variability and energy-balance implications of surface ponds on Himalayan debris-covered glaciers’ has combined remote sensing, field surveys, and numerical modelling to understand the role of supraglacial ponds.

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Figure 1: Evan Miles and Anna Chesnokova installing thermistor strings and a pressure transducer in a supraglacial pond on Lirung Glacier, May 2014.

 

New OA paper studying spatio-temporal variability of supraglacial ponds

Evan and several other team members have just had an Open Access paper published in the Journal of Glaciology based on one aspect of Evan’s doctoral work, Spatial, seasonal and interannual variability of supraglacial ponds in the Langtang Valley of Nepal, 1999–2013.  The study uses 15 years of Landsat data (172 scenes) to analyse the variability of supraglacial ponds on a set of five debris-covered glaciers.  This is a major advance in several ways, as prior studies have used only a few scenes to assess ponded area for debris-covered glaciers.  The use of such an extensive dataset allowed the authors to also assess the spatial patterns of ponding and interannual changes in pond cover in a more robust way than has been done previously.

 

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Figure 2: Spatial distribution of supraglacial ponds as percent of May–October observations (n =68), also showing results for other lakes outside the debris-covered tongues (orange ellipses), 1999–2013.

 

One of the most important results is the seasonal variability of ponds, which controls the role they can play in a glacier’s mass balance.  Expect more news on that topic soon!

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Figure 3: Seasonal pattern of thawed pond cover as percent of observable debris-covered glacier area, with individual scenes coloured by year of observation (n =172) and dot tails highlighting the effect of a 34% overestimation of pond area. The solid black line is the monthly mean, with dashed lines showing the ± 1σ spread.

 

Evan Miles to start Post-Doc in Leeds

Finally, Evan has accepted a two-year research position at the University of Leeds to work with Dr Duncan Quincey, Dr Bryn Hubbard (Aberystwyth University), and Dr Ann Rowan (Sheffield University) as part of the NERC-funded EverDrill project. This is an exciting and ambitious effort to drill to the bed of Khumbu Glacier and install a sensor suite to understand englacial and subglacial processes, a first for the Himalaya, and a critical need identified by other MountainHydrology team members.  More project info can be found here.  Evan will continue to be peripherally involved in many MountainHydrology projects.

New paper: climate change impacts on upper Indus basin hydrology

The Indus is one of the most meltwater-dependent rivers on Earth, and hosts a large, rapidly growing population and the world’s largest irrigation scheme. Understanding the hydrology of the upper Indus basin is challenging. The Hindu Kush, Karakoram and Himalayan mountain ranges are difficult to access, hampering field measurements of meteorological, glaciological and hydrological processes. These processes are therefore still poorly understood. To make it more complex, climate change projections for the Indus basin show a very large spread. In our recent (open access) paper published in PLoS ONE we present hydrological projections for the 21st century in the upper Indus basin, based on a cryospheric-hydrological model forced with an ensemble of downscaled GCM outputs.

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The Hunza river in front of the Passu cones (upper Indus basin).

 

Three methodological advances are introduced:

  • A new precipitation dataset that corrects for the underestimation of high-altitude precipitation is used.
  • The model is calibrated using data on river runoff, snow cover and geodetic glacier mass balance.
  • An advanced statistical downscaling technique is used that accounts for changes in precipitation extremes.

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Our projections indicate decreases in glacier melt contribution in favor of snow melt and rainfall-runoff contribution to stream flow in the upper Indus basin, at the end of the 21st century.

 

The focus of the analysis in our study is not only on changes in sources of runoff and water availability but also on changes in seasonality and hydrological extremes, which are still large unknowns in the upper Indus basin. We conclude that the upper Indus basin faces a very uncertain future in terms of water availability towards the end of the 21st century. Despite the large uncertainties in future climate and water availability, basin-wide patterns and trends of intra-annual shifts in water availability are consistent across climate change scenarios. For the near future these trends mainly consist of minor increases in summer flows combined with increased flows during other seasons. For the far future the trends show decreases in summer flows combined with stronger increasing flows during the other seasons. Furthermore, increases in intensity and frequency of extreme discharges are found for most of the upper Indus basin and for most scenarios and models considered, implying increases in flooding events during the 21st century.

The study is presented at the AGU Fall meeting in San Francisco on Monday, 12 December 09:15 – 09:30, Moscone West – 3005

 

extremes

Analysis of future changes indicates increases in the frequency and magnitude of extreme flows for most of the UIB and most of the climate change scenarios.

New ICIMOD video on our Himalayan research

We know very little about glaciers in the high mountains. We know they’re shrinking and temperatures are rising faster at higher altitudes than anywhere else on the planet. But, due to extreme conditions and inaccessibility, we have much to learn. Detailed field measurements are being made on just twelve out of some 54,000 glaciers in the Himalayas. More measurements are needed because these glaciers feed the rivers people living down below rely on.

 


Directed and produced by Susan Hale Thomas

New paper: investigations on debris-covered glaciers

Glaciers covered by debris – rocks, dirt, silt, and sand – are common in the Himalayas. Depending on who’s counting (and where you are looking), debris covers nearly 25% of the total glacierized area in the region.  Experiments and previous studies have shown that really thin debris enhances melt, but that anything over 2 cm thick insulates the ice melt.  But what is the net effect of debris cover on glacier melt rates? Our recently published (open access) paper in the Cryosphere tries to answer this question.

 

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Khumbu Glacier (center) is debris covered. So is the bottom 2/3 of Changri Nup Glacier, located to the west. Everest is at the far right of this Landsat scene.

 

Unfortunately, the answer is not so easy to obtain. Traditional mass balance stake measurements are (a) difficult to install and maintain on debris-covered glaciers, and (b) impossibly biased towards locations where it is possible to drill. You could look at surface elevation changes over part of the glacier with either photogrammetry, UAV, or satellite (we use all three), but if you do this you also need to consider the emergence velocity (or increase in elevation) of the glacier as it flows downhill. On any given point in the ablation zone, the total surface elevation change is a function of both emergence and melt. And to estimate the mean emergence velocity, you need to measure the ice flux through a cross-section of the glacier.

 

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Rates of surface elevation change at Changri Nup Glacier for different periods and data sources: (A) 2011 – 2014 (photogrammetry); (B) 2011 – 2015 (photogrammetry and UAV); (C) 2009 – 2014 (satellite and photogrammetry)

 

Christian Vincent and Patrick Wagnon, French glaciologists from Laboratoire de Glaciologie et Geophysique (LGGE) and Institut de Recherche pour le Development (IRD), have collected multiple datasets over 4 years to estimate the mass gain and loss over the debris-covered Changri Nup Glacier. I’d remind you that debris-covered glaciers at 5400 m of elevation are not among the easiest places to work.

But together with a team of co-authors they have measured surface velocities and surface melt rates with ablation stakes; developed digital elevation models from photogrammetry in 2011 and 2014, from unmanned aerial vehicle surveys in 2015, and from high-resolution satellite data in 2009; measured ice depths with ground-penetrating radar, and mapped ground control points and elevation profiles with differential GPS.

 

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The lead author C. Vincent uses a differential GPS to measure a ground control point for UAV flights over the clean Changri Nup.

 

And the overall result: melt rates on the debris-covered glacier are about 60% less than what they would be if the glacier was free of debris. Ice cliffs and ponds enhanced melt locally, but not enough to offset the overall reduction in melt caused by the debris. The surface mass balance (in m of water equivalent, or m w.e.) over the debris-covered tongue, inferred from average surface lowering of -0.81 m w.e./yr and an average emergence velocity of +0.37 m w.e./yr, is -1.21 m w.e./yr. If the glacier were debris-free, we would expect to see an average mass balance rate of -3.00 m w.e./yr.

This field-based study provides strong evidence that the ‘debris-cover anomaly’ (where satellite data show that debris-covered glaciers appear to be lowering at the same rate as clean-ice glaciers) is an artifact. It also shows that, in this location at least, the effects of ponds and ice cliffs are minimal.

Why is this important? If debris-covered ice (low-angle and thick) occupies 25% of the total glacierized area, it probably contains an even greater percentage of the total ice volume. Better estimates of the net insulating effect of debris will help us improve simulations of future ice loss, and its impacts on water resources downstream.

 

This is a re-post of a recent blog by Joseph M. Shea.

Martian crater officially named Langtang

To honor Langtang, the village that was tragically destroyed by an avalanche triggered by the Nepal earthquake of April 2015, we proposed to name a Martian crater after Langtang. The idea was initiated by colleague Tjalling de Haas, who investigates debris flows and land-forms on Mars. The request was officially approved by the International Astronomical Union and Langtang will now forever be remembered, even on Mars. The crater has a diameter of 12 km and interesting enough contains glacial land-forms and the moraines of the Last Mars Glacial Maximum and the debris fans formed after the glaciers melted are clearly visible.

 

The Langtang Crater

The Langtang Crater

 

 

 

 

 

 

 

 

 

 

 

Debris flows in the Langtang Crater

Debris flows in the Langtang Crater

 

 

 

 

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