Exploring uncertainty in glacier mass balance modelling with Monte Carlo simulation

Machguth, Horst; Purves, Ross S.; Oerlemans, J.; Hoelzle, Martin; Paul, Frank

doi:10.5194/tc-2-191-2008

Cited by 71 publications

(38 citation statements)

References 27 publications

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“…Furthermore, it has been frequently used in impact model applications (e.g. Corripio, 2002;Gruber, 2005;Machguth et al, 2008;Helbig et al, 2009) as well as other studies aiming at an optimal use of solar power, for example (Schillings, 2004). The Iqbal (1983) model assumes a homogeneous atmosphere and uses an isotropic view factor approach.…”

Section: S Gubler Et Al: Uncertainties Of Parameterized Surface Sdrmentioning

confidence: 99%

Uncertainties of parameterized surface downward clear-sky shortwave and all-sky longwave radiation.

2012

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Abstract.As many environmental models rely on simulating the energy balance at the Earth's surface based on parameterized radiative fluxes, knowledge of the inherent model uncertainties is important. In this study we evaluate one parameterization of clear-sky direct, diffuse and global shortwave downward radiation (SDR) and diverse parameterizations of clear-sky and all-sky longwave downward radiation (LDR). In a first step, SDR is estimated based on measured input variables and estimated atmospheric parameters for hourly time steps during the years 1996 to 2008. Model behaviour is validated using the high quality measurements of six Alpine Surface Radiation Budget (ASRB) stations in Switzerland covering different elevations, and measurements of the Swiss Alpine Climate Radiation Monitoring network (SACRaM) in Payerne. In a next step, twelve clear-sky LDR parameterizations are calibrated using the ASRB measurements. One of the best performing parameterizations is elected to estimate all-sky LDR, where cloud transmissivity is estimated using measured and modeled global SDR during daytime. In a last step, the performance of several interpolation methods is evaluated to determine the cloud transmissivity in the night.We show that clear-sky direct, diffuse and global SDR is adequately represented by the model when using measurements of the atmospheric parameters precipitable water and aerosol content at Payerne. If the atmospheric parameters are estimated and used as a fix value, the relative mean bias deviance (MBD) and the relative root mean squared deviance (RMSD) of the clear-sky global SDR scatter between between −2 and 5 %, and 7 and 13 % within the six locations. The small errors in clear-sky global SDR can be attributed to compensating effects of modeled direct and diffuse SDR since an overestimation of aerosol content in the atmosphere results in underestimating the direct, but overestimating the diffuse SDR. Calibration of LDR parameterizations to local conditions reduces MBD and RMSD strongly compared to using the published values of the parameters, resulting in relative MBD and RMSD of less than 5 % respectively 10 % for the best parameterizations. The best results to estimate cloud transmissivity during nighttime were obtained by linearly interpolating the average of the cloud transmissivity of the four hours of the preceeding afternoon and the following morning.Model uncertainty can be caused by different errors such as code implementation, errors in input data and in estimated parameters, etc. The influence of the latter (errors in input data and model parameter uncertainty) on model outputs is determined using Monte Carlo. Model uncertainty is provided as the relative standard deviation σ rel of the simulated frequency distributions of the model outputs. An optimistic estimate of the relative uncertainty σ rel resulted in 10 % for the clear-sky direct, 30 % for diffuse, 3 % for global SDR, and 3 % for the fitted all-sky LDR.

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Section: S Gubler Et Al: Uncertainties Of Parameterized Surface Sdrmentioning

confidence: 99%

Uncertainties of parameterized surface downward clear-sky shortwave and all-sky longwave radiation.

2012

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“…Similarly, intercomparison projects of runoff models by the World Meteorological Organization (e.g., WMO, 1986) revealed that simple models provided results comparable to more sophisticated models, given the difficulties of assigning proper model parameters and meteorological input data to each catchment element. Machguth et al (2008), analyzing model uncertainty with Monte Carlo simulations at one point on the tongue of Morteratsch Glacier in Switzerland, concluded that the output of well-calibrated models, when applied to extrapolate in time and space, is subject to considerable uncertainties due to the quality of input data. According to Carturan et al (2012a), who compared three melt algorithms in a 6-year application of an enhanced temperature-index model over two Italian glaciers, uncertainties in extrapolating temperature measurements from off-site data partly mask the peculiar behavior of each algorithm and do not allow definitive conclusions to be drawn.…”

Section: Introductionmentioning

confidence: 99%

Air temperature variability over three glaciers in the Ortles–Cevedale (Italian Alps): effects of glacier fragmentation, comparison of calculation methods, and impacts on mass balance modeling

et al. 2015

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Abstract.Glacier mass balance models rely on accurate spatial calculation of input data, in particular air temperature. Lower temperatures (the so-called glacier cooling effect) and lower temperature variability (the so-called glacier damping effect) generally occur over glaciers compared to ambient conditions. These effects, which depend on the geometric characteristics of glaciers and display a high spatial and temporal variability, have been mostly investigated on medium to large glaciers so far, while observations on smaller ice bodies ( < 0.5 km 2 ) are scarce. Using a data set from eight on-glacier and four off-glacier weather stations, collected in the summers of 2010 and 2011, we analyzed the air temperature variability and wind regime over three different glaciers in the Ortles-Cevedale. The magnitude of the cooling effect and the occurrence of katabatic boundary layer (KBL) processes showed remarkable differences among the three ice bodies, suggesting the likely existence of important reinforcing mechanisms during glacier decay and fragmentation. The methods proposed by Greuell and Böhm (1998) and Shea and Moore (2010) for calculating on-glacier temperature from off-glacier data did not fully reproduce our observations. Among them, the more physically based procedure of Greuell and Böhm (1998) provided the best overall results where the KBL prevails, but it was not effective elsewhere (i.e., on smaller ice bodies and close to the glacier margins). The accuracy of air temperature estimations strongly impacted the results from a mass balance model which was applied to the three investigated glaciers. Most importantly, even small temperature deviations caused distortions in parameter calibration, thus compromising the model generalizability.

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“…(e.g., Gurgiser et al, 2013;Machguth et al, 2008). In order to minimize respective uncertainties in the mass balance model, we made recourse of a calibration procedure which integrates available snow information.…”

Section: Model Tuning For Individual Stakes and Yearsmentioning

confidence: 99%

“…This stake was chosen as the relatively homogeneous surrounding makes it representative for a wider region of the glacier and it offers by far the highest number of stake readings in the upper region of Langenferner. It is hence the best choice for the optimization of model parameters, which was done applying a Monte Carlo approach (e.g., Machguth et al, 2008;Mölg et al, 2012) performing 1000 model runs with different parameter combinations in order to find the best model setting for the local conditions. The optimal parameter combination was then applied to all stake locations in the upper glacier part.…”

Section: Monte Carlo Optimization Of Model Parametersmentioning

confidence: 99%

Reanalysis of a 10-year record (2004–2013) of seasonal mass balances at Langenferner/Vedretta Lunga, Ortler Alps, Italy

et al. 2017

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Abstract. Records of glacier mass balance represent important data in climate science and their uncertainties affect calculations of sea level rise and other societally relevant environmental projections. In order to reduce and quantify uncertainties in mass balance series obtained by direct glaciological measurements, we present a detailed reanalysis workflow which was applied to the 10-year record (2004 to 2013) of seasonal mass balance of Langenferner, a small glacier in the European Eastern Alps. The approach involves a methodological homogenization of available point values and the creation of pseudo-observations of point mass balance for years and locations without measurements by the application of a process-based model constrained by snow line observations. We examine the uncertainties related to the extrapolation of point data using a variety of methods and consequently present a more rigorous uncertainty assessment than is usually reported in the literature.Results reveal that the reanalyzed balance record considerably differs from the original one mainly for the first half of the observation period. For annual balances these misfits reach the order of > 300 kg m −2 and could primarily be attributed to a lack of measurements in the upper glacier part and to the use of outdated glacier outlines. For winter balances respective differences are smaller (up to 233 kg m −2 ) and they originate primarily from methodological inhomogeneities in the original series. Remaining random uncertainties in the reanalyzed series are mainly determined by the extrapolation of point data to the glacier scale and are on the order of ±79 kg m −2 for annual and ±52 kg m −2 for winter balances with values for single years/seasons reaching ±136 kg m −2 . A comparison of the glaciological results to those obtained by the geodetic method for the period 2005 to 2013 based on airborne laser-scanning data reveals that no significant bias of the reanalyzed record is detectable.

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Exploring uncertainty in glacier mass balance modelling with Monte Carlo simulation

Cited by 71 publications

References 27 publications

Uncertainties of parameterized surface downward clear-sky shortwave and all-sky longwave radiation.

Uncertainties of parameterized surface downward clear-sky shortwave and all-sky longwave radiation.

Air temperature variability over three glaciers in the Ortles–Cevedale (Italian Alps): effects of glacier fragmentation, comparison of calculation methods, and impacts on mass balance modeling

Reanalysis of a 10-year record (2004–2013) of seasonal mass balances at Langenferner/Vedretta Lunga, Ortler Alps, Italy

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