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Downscaling of the global climate model data for the mass balance calculation of mountain glaciers

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In this paper, we consider a hybrid method of downscaling of GCM-generated meteorological fields to the characteristic spatial resolution utilized for modeling of a single mountain glacier mass balance. The main goal of the study is elaboration of a reliable prediction method for evaluation of future states of mountain glaciation under changing climatic conditions.
A method consists of two stages. On the first, dynamical stage, we use the results of calculations of regional numerical model HadRM3P for Black Sea-Caspian region with a spatial resolution of 25 km [9]. Initial conditions for HadRM3P are provided by a GCM developed in the Institute of Numerical Mathematics of RAS (INMCM4) [4]. Calculations were carried out for two time slices: the present climate (1971-2000 years) and climate in the late 21st century (2071-2100 years) according to scenario of greenhouse gas emissions RCP 8.5.
On the second stage of downscaling, further regionalization is achieved by projecting of RCM-generated data to the high-resolution (25 m) digital elevation model in a domain enclosing a target glacier. Elevation gradient of surface air temperature and precipitation were derived from the model data. Further both were corrected using data of observations. The incoming shortwave radiation is calculated in the mass balance model separately, taking into account slope, aspect and shade.
Further, the method was tested for surface mass-balance calculation of Marukh Glacier (Western Caucasus), both for present-day and for future climate. In the end of the 21st century expected air temperature growth here for the summer months is about 5-6 °C, for winter - 2-3 °C. Reduction in annual precipitation is not significant, less than 10%. Increase in absorbed shortwave radiation will be about 5%. These changes yield in shifting of ELA higher than present-day Marukh upper part. This will inevitably cause degradation of the glacier and its gradual disappearance. The main contribution to glacier shrinking and disappearance will be made by air temperature rise, because it will affect the change in the ratio of ablation and accumulation areas. Besides, increase in temperature will cause extension of the average melting season duration. These are, of cause, preliminary result illustrating how downscaling method works. We did not take into account dynamic effects and gradual reduction of glaciated area. In future, we plan to couple mass balance and dynamical models [16] and to force them with downscaled climate change in order to account for transient glacier changes.
Tijdschrift: Lëd i Sneg
ISSN: 2076-6734
Issue: 4
Volume: 57
Pagina's: 437-452
Aantal pagina's: 16
Jaar van publicatie:2017
Trefwoorden:air temperature, Caucasus, climate scenario, downscaling, glacier, mass balance, precipitations, regional model