Vadret da Morteratsch (Switzerland) between 1864 and 2100

Vadret da Morteratsch (Switzerland) between 1864 and 2100:
dynamics, geometry and mass balance
* [email protected]
Harry Zekollari*, Heiko Goelzer, Johannes Jakob Fürst and Philippe Huybrechts
Abstract: TH-29_A5.5
Earth System Sciences & Departement Geografie, Vrije Universiteit Brussel, Brussels, Belgium.
Setting
Abstract
•  Engadin valley (Switzerland)
•  Glacier complex consists of
two connected glaciers:
§  Vadret da Morteratsch (M)
§  Vadret Pers (P)
M
P
We use a glacier flow model for Vadret da Morteratsch (Engadin, Switzerland) to better understand its strong retreat since the end
of the Little Ice Age (LIA) and to study its further disintegration under future warming. The 3-D higher-order glacier flow model is
implemented on a 25 m horizontal resolution. The sliding and rate factors are tuned to reproduce measured surface velocities. The
model is coupled to a 2-D energy-balance model, which takes into account a parameterization of the surface energy fluxes, the
shading effect of surrounding mountains and changes in snow thickness affecting the albedo.
The observed frontal retreat since 1864 is reconstructed by forcing the mass balance model with monthly temperature and
precipitation data from nearby meteorological stations. The modelled glacier evolution is validated by comparing it with past extents
known from topographic maps and volume changes derived from DEM differencing.
Based on the Swiss Climate Change Scenarios CH2011, the future evolution of the glacier is simulated. Results indicate that due to
its slow response, the present glacier geometry is severely out of equilibrium with today's climate. Even without additional warming
a strong retreat and mass loss are projected for the coming century and the Vadret da Morteratsch disconnects from its main
tributary, Vadret Pers. Assuming a warming of more than 3°C by 2100, only isolated ice patches remain at high elevation. These are
largely stagnant and precede the almost total demise of the glacier complex if the same climate conditions were sustained beyond
that period.
Methodology
Evolution of the glacier in time
1864à2010
•  Starting point is steady state with Little Ice Age (LIA) extent of the glacier
•  Period 1864 à 1960: dynamic calibration (bias added on top of calculated mass balance
field), because:
o  LIA: glacier was not in steady state! Causes initial error
o  Error mass balance forcing: climatic input and model uncertainty
•  After 1960: no calibration needed anymore to reproduce the observed frontal retreat
because of correct history and reduced uncertainty!
•  Validation based on several sources:
o  Length records and areal extent from topographic maps
o  Volume evolution from Huss et al. (2010), based on mass balance modelling
and Digital Elevation Model (DEM) differencing (1935, 1955, 1985 and 2008)
Ice thickness & bedrock elevation (Zekollari et al., 2013)
2010
•  Bedrock = surface elevation – ice thickness. Overdeepening for central Morteratsch
Diagnostic velocity reconstruction (Zekollari et al., 2013)
2010à2100
•  Climatic forcing (w.r.t. 1981-2010): Based on CH2011 scenarios: strongest warming in summer, dry summers, wet winters
•  Even without additional warming: strong frontal retreat and disconnection of both glaciers
•  Warmest scenarios: at end of century only ice at high elevation. Likely formation of proglacial lakes in bedrock depressions
Take away
•  Best fit between observed and modelled
velocities:
o  Flow parameter: A : 6.0 x 10-16 m7 N-3 a-1
o  Sliding parameter: Asl : 1.8 x 10-16 Pa-3 a-1
•  H i g h ve l o c i t i e s fo r c e n t ra l u p p e r
Morteratsch: more than 120 m a-1.
•  Front and confluence area almost stagnant
à limited mass supply
à glacier thinning ≈ yearly ablation!
•  Reconstruction of the past is needed: (i) for model validation, (ii) because future evolution is partly determined by past and
present-day glacier evolution and dynamics
•  Future: strong retreat under all scenarios, even without additional warming
•  Need detailed high resolution studies of individual ice masses to improve understanding of glacier retreat and dynamics and to
ameliorate global/large-scale simulations of future glacier evolution
•  Ice thickness + model tuning: Zekollari et al. (2013)
•  Prognostic simulations (1864 à 2100): to be submitted soon…
References
•  Fürst, J.J., O. Rybak, H. Goelzer, B. De Smedt, P. de Groen, and P. Huybrechts (2011), Improved convergence and stability properties in a three-dimensional
higher-order ice sheet model, Geosci. Model Dev., 4, 1133-1149, doi: 10.5194/gmd-4-1133-2011
•  Huss, M., S. Usselmann, D. Farinotti, and A. Bauder (2010), Glacier mass balance in the south-eastden Swiss Alps since 1900 and perspectives for the
future, Erdkunde, 64(2), 119-140, doi: 10.3112/erdkunde.2010.02.02
•  Nemec, J., P. Huybrechts, O. Rybak, and J. Oerlemans (2009), Reconstruction of the annual balance of Vadret da Morteratsch, Switzerland, since 1865, Ann.
Glac., 50(50), 126-134, doi: 10.3189/172756409787769609
•  Zekollari, H., P. Huybrechts, J.J. Fürst, O. Rybak, and O. Eisen (2013), Calibration of a higher-order 3-D ice flow model of the Morteratsch glacier complex,
Engadin, Switzerland, Ann. Glac., 57(63), 343-351, doi: 10.3189/2013AoG63A434