Adding the Long-Term Perspective: Tien Shan’s Glacier Mass Change during 1961-2012

The Tien Shan, Central Asia's major mountain range, has recently been the focus of a series of studies targeting changes in meteorological variables, glacier mass and extent, as well as runoff. Reviews have repeatedly highlighted the importance of glacier melt for total runoff on the one hand, but the scarcity of direct glaciological observation on the other. At the regional to global scale, the lack of such direct observations has been tackled by using remotely sensed products such as satellite gravimetry and altimetry, but the covered time frame is typically in the order of one decade, thus hampering robust assessments.

Here, an ensemble of approaches based on the Gravity Recovery and Climate Experiment (GRACE), the Ice, Cloud and land Elevation Satellite (ICESat), and in-situ glacier mass balance measurements is used for estimating glacier mass changes in the Tien Shan during the last decade, and for validating a glacier mass balance model that we subsequently use for reconstructing a continuous mass balance time series over the last half-century. The model ensemble is designed to take into account a wide range of uncertainty sources including often-neglected differences such as data sources or model structure.

We cross-validate our different approaches during the period 2003-2009, and find an average glacier mass change of -6.1±4.4 Gt/a, thus confirming previously published estimates. We use the glaciological modelling approach to extend our estimates over the period 1961-2012, and gain insights in the spatial and temporal evolution of the regional glacier melt. Estimated melt rates are in turn used for assessing the contribution of glacier melt to the total runoff of major hydrological basins, and indicate that the contribution from glaciers has likely been overestimated in a series of previous studies.