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Reconstruction of the Historical (1750–2020) Mass Balance of Bordu, Kara-Batkak and Sary-Tor Glaciers in the Inner Tien Shan, Kyrgyzstan
The mean specific mass balance of a glacier represents the direct link between a glacier
and the local climate. Hence, it is intensively monitored throughout the world. In the Kyrgyz
Tien Shan, glaciers are of crucial importance with regard to water supply for the
surrounding areas. It is therefore essential to know how these glaciers behave due to
climate change and how they will evolve in the future. In the Soviet era, multiple
glaciological monitoring programs were initiated but these were abandoned in the
nineties. Recently, they have been re-established on several glaciers. In this study, a
reconstruction of the mean specific mass balance of Bordu, Kara-Batkak and Sary-Tor
glaciers is obtained using a surface energy mass balance model. The model is driven by
temperature and precipitation data acquired by combining multiple datasets from
meteorological stations in the vicinity of the glaciers and tree rings in the Kyrgyz Tien
Shan between 1750 and 2020. Multi-annual mass balance measurements integrated
over elevation bands of 100m between 2013 and 2020 are used for calibration. A
comparison with WGMS data for the second half of the 20th century is performed for
Kara-Batkak glacier. The cumulative mass balances are also compared with geodetic
mass balances reconstructed for different time periods. Generally, we find a close
agreement, indicating a high confidence in the created mass balance series. The last
20 years show a negative mean specific mass balance except for 2008–2009 when a
slightly positive mass balance was found. This indicates that the glaciers are currently in
imbalance with the present climatic conditions in the area. For the reconstruction back
to 1750, this study specifically highlights that it is essential to adapt the glacier geometry
since the end of the Little Ice Age in order to not over- or underestimate the mean
specific mass balance. The datasets created can be used to get a better insight into
how climate change affects glaciers in the Inner Tien Shan and to model the future
evolution of these glaciers as well as other glaciers in the region.