Category Archives: Uncategorized

New study on glacier response to natural and anthropogenic climate change

Ongoing global warming has resulted in a widespread retreat of glaciers since the end of the Little Ice Age, having important consequences for the society and the environment. There is a wide debate about the extent humans can be considered as responsible for the glacial retreat we observe nowadays. Over the 20th century the anthropogenic influence on the climate system has increased and according to a few global studies this signal has become a prevalent explanation for the observed decrease in glacier mass since the 1980s. These studies have however mainly investigated historical glacier changes with a focus on changes in glacier mass balance solely, whereas several studies have indicated that a relation between glacier dynamics and thinning rates exist. For this reason, the coupling between mass balance models and ice flow models with a sufficient representation of glacier dynamics is crucial.

Observed (OBS) and simulated (SIM) mean surface elevation change (A,B,E,F) and velocities (C,D,G,H) for the Langtang (A–D) and Hintereisferner (E–H) glaciers. Line 6 indicates the location of stone line 6 (Span et al., 1997). Source of the observed mean surface elevation change grids are Ragettli et al. (2016) for the Langtang Glacier and Klug et al. (2018) for the Hintereisferner.

A new study published (open access) in Frontiers in Earth Sciences led by René assesses the response of glaciers to natural and anthropogenic climate change from the end of the Little Ice Age (1850) to the present-day (2016). A coupled glacier mass balance and dynamical ice flow model was developed and applied to two glaciers with contrasting surface characteristics: the debris-covered Langtang Glacier (Nepal) and the clean-ice Hintereisferner (Austria). The model was forced with four climate models from the historical experiment of the CMIP5 archive, which represent region-specific warm-dry, warm-wet, cold-dry, and cold-wet climate conditions. To isolate the effects of anthropogenic climate change on glacier mass balance and dynamics runs are selected from the climate models with and without further anthropogenic forcing after 1970 until 2016.

Simulations showing changes in the geometry of Langtang Glacier and Hintereisferner between 1850 and 2010 under cold-wet and cold-dry anthropogenic climate conditions, respectively (Click for animation).

The findings of this study indicate that both glaciers experience the largest reduction in area and volume under warm climate conditions, and the simultaneously surface velocities generally decrease over time. Without further anthropogenic forcing the findings reveal a 3% (9%) smaller decline in glacier area (volume) for the debris-covered glacier and a 18% (39%) smaller decline in glacier area (volume) for the clean-ice glacier, which indicates that the response of the two glaciers can mainly be attributed to anthropogenic climate change. Here, the debris-covered glacier shows a limited retreat and tends to lose less mass due to insulation of the glacier surface by a layer of supraglacial debris, where the clean-ice glacier responds faster to climate change and shows a larger retreat.

 

 

Sediment supply from lateral moraines to a debris-covered glacier in the Himalaya

A number of studies in our group have looked at debris-covered glaciers in recent years. What we have not really done yet is ask where the debris covering all that ice is actually coming from. In a new study, published recently in the Journal of Earth Surface Dynamics we are examining the contribution of sediment from the lateral moraines to the glacier surface.

Using repeat DEMs from multiple UAV flights between 2013 and 2018, we show that debris from the moraines can only reach the margins of the glacier surface but locally contributes to a considerable thickening of the cover.

 

The analysis shows that mass transport results in an elevation change on the lateral moraines with an average rate of +0.31m/year during this period, partly related to sub-moraine ice melt. There is a higher elevation change rate observed in the monsoon (+0.39 m/year) than in the dry season (+0.23 m/year).

The lower debris aprons of the lateral moraines decrease in elevation at a faster rate during both seasons, due to both the melt of ice below and mass wasting processes at the surface. The surface lowering rates of the upper gullied moraine, with no ice core below, translate into an annual increase in debris thickness of 0.08 m/year along a narrow margin of the glacier surface. Here the observed debris thickness is approximately 1 m, reducing melt rates of underlying glacier ice.

 

The paper and associated data is available open access here: https://www.earth-surf-dynam.net/7/411/2019/

Modelling melt in high mountain Asia – new study testing different models in Nature Scientific Reports

We recently published a new paper, led by Maxime Litt, providing guidelines for glacier-ablation modelling in HMA environments.

The conventional Temperature index (TI) models for modelling glacier ablation require few input variables and rely on simple empirical relations. The approach is assumed to be reliable at lower elevations (below 3500 m above sea level, a.s.l) where air temperature relates well to the energy inputs driving melt. Using field meteorological observation in Langtang and Khumbu, we show that temperature relates poorly to a number of important mass-loss drivers in high-altitude, so that temperature indexes have to be handled with care.

At the high elevation glaciers in Mountain Asia (HMA), we observed that incoming shortwave radiation is the dominant energy input and the full surface energy balance model relates only partly to daily mean air temperature. During monsoon surface melt dominates ablation processes at lower elevations (between 4950 and 5380 m a.s.l.). As net shortwave radiation is the main energy input at the glacier surface, albedo and cloudiness play key roles while being highly variable in space and time. For these cases only, ablation can be calculated with a TI model. Sublimation and other wind-driven ablation processes are important for mass loss, and remain unresolved with such simple methods. Ablation modeled with a SEB can diverge from the observations, but a suitable value for surface roughness can solve the issue.

Cumulated ablation calculated with the surface lowering measurements (thick blue line), with the surface energy balance for changing z0 values (orange dashed and continuous lines), with the TI (red line) and ETI (clear blue line) with one fixed set of factors. The hourly wind speed is shown upside down (green curve). Periods of surface melt (Ts = 0) are highlighted in orange. Results from Mera Glacier, 5380 m a.s.l in 2014 and 2017 (a) from Yala Glacier, 5350 m a.s.l., in 2014, 2016 (b) and Mera Glacier, 6352 m a.s.l, in 2015 and 2016 (c).

Read the paper in detail here.

Field Work Symphony

We collect most of the data we use in our research in the field, in recent years to a large degree in the Nepalese Himalayas. Field work can have effects on your health – it’s cold, oxygen levels are low, work is exhausting and you are always a bit nervous about whether the next sensor you read out will actually have any data stored. All we have is ourselves – there is no internet or phone connection in our field site, there are showers, however not all team members know how to use it. We realized that this exhaustion somehow articulates itself by lack of sleep and weird songs stuck in your head. For the sake of future research in high altitude psychology we decided to document this mess from our recent trip to Langtang in October.

All the songs listed suddenly surfaced – mostly while walking – as humming or whistling by some team member and then quickly spread through the group and sometimes remained for days in our heads or quickly disappeared again. Most of them made us laugh, many were a nuisance and for some reason very few were actually good music.

To give you an idea of the deteriorating path we took during nearly 6 weeks in the field I’ll start at the very end. While by all common standards we could be declared more or less sane at the start of our work, on the very last day of our trip Joe, an outstanding musician and singer who has played on stages in a number of countries and myself, trained in classical music at University and hence supposedly with a good taste by upbringing, sang and danced respectively to …

The closest we got to putting a ring somewhere was the ring memory of our sturdy Campbell Scientific CR1000. We were joined by a completely hammered Nepali soldier looking for cigarettes, alcohol and entertainment and our steadfast porters who must wonder again and again whether the work we produce is actually worth anything at all considering our behaviour after a day’s work.

When we were asked by our local porters to sing our field song at parties that were regularly thrown in the kitchen tent or lodge we stayed in, for some strange reason we would sing

regularly, strange because the only Italian on the team hated it and none of the rest speak any Italian.

To reach our stations at the very back of the valley we always have an easy half day hike along the main river of the catchment. This year we could witness wild boars along the sand banks and yak herds crossing the forceful stream which we could only cross on bridges made from flagpoles.

The rockfalls along the river as a result of the earthquake in 2015 are impressive.

Having reached our camp, we played cards the whole evening sipping some of Joe’s fine treat – Whiskey transported in a Nalgene bottle. Like every night our kitchen staff would come around after a while and fill up our bottles with hot water for the night. In the dark, nobody noticed the difference between the half full Nalgene and the other water bottles. The result was a lukewarm, diluted Whiskey. Quite a downer at that point.

Remembering Whiskey ...

Remembering Whiskey …

Although we do make quite silly mistakes at times especially when working very high when the exhaustion and oxygen loss really kicks in perceptibly we do seem to be able to find matching song texts for the occasion. “Plug out that cable!” …”Are you sure? Do you really want that? Really really …?”

And likely on the approach to reading out a precious datalogger in the remotest location (although I’m not sure where that song popped up)

Many of those “earworms” as we call them in German were such a nuisance and difficult to get rid of, that Joe with everyone roped up on the glacier above 5300 m suddenly called for a halt. “Can you please help me get rid of that song in my head?”

Aptly for those sometimes quite difficult ascents at this elevation there was

at one point. That surely came from my side since I also come up with other romantic hogwash like Bryan Adams. But it seems that song only comes to me below a certain 02 threshold, I fail to remember which one it was.

After 3 days in high camp – if you wonder, that’s what it looks like if you can’t sleep:

– words and sanity left us completely and for a few hours the “refrain” of

became a thing. Luckily didn’t last long.

Neither did

which hit Joe’s patriotic side next to a Pluviometer in horrible weather.

What our team of porters produces in this environment on the culinary side is always impressive. So are the views during the day and at night.

Before we are served dinner in our high altitude restaurant, we do get a bowl of soup which prompts everyone to crawl out of the tent again, stopping the late afternoon nap or field report writing. For some unbeknown reason I always whistle

during soup time. I’m too young for the Archies and didn’t even know the song. But always a team, Joe helped out and quickly put a title to my annoying habit.

We arrived back in Kathmandu in a horrible Jeep on a congested road with a song on the MP3 on repeat that really never should have existed.

Well, if you wonder what output we produce with that background noise come and see our talks and posters at AGU this week.

Mountainhydrology at AGU 2016

Mountainhydrology will be at AGU Fallmeeting 2016 the coming week with a whole bunch of exciting posters and talks. Drop by, say hi and ask us on advice on how to fall asleep when a 800kg Yak incessantly burps next to your tent.

On Monday Arthur will kick off with a talk on his recent paper on future shifts and extremes in the Indus basin at 0915 at Moscone West 3005.

The same day and same location at 4pm Walter will talk about recent advances in understanding climate, river and glacier dynamics in High Mountain Asia.

On Thursday morning Philip will show the findings from his recent paper on surface features on Langtang glacier at Moscone South. At the same location in the afternoon Jakob will present recent work on High Mountain Asia topography.

Finally on Friday morning at 0830 Francesca will give an overview over recent advances on debris covered glaciers and Pascal will follow with his talk on cliff modelling at Moscone West 3007.