Geodetic glacier mass balance in the Karakoram (2011–2019) from TanDEM-X: An InSAR DEM differencing framework

Glaciers serve as sensitive indicators of climate change, influencing both regional water supplies and global sea-level rise. Contrasting to the global tendency towards retreat, glaciers in the Karakoram exhibits an unusual pattern of stability and modest thickening. However, the spatial variability and underlying causes of the mass balance anomalies remain insufficiently understood, primarily due to the limitations in previous measurement methods. To address this gap, we conducted a comprehensive geodetic analysis of glacier elevation changes in the central and eastern Karakoram, covering 681 glaciers of over 10,000 km² between 2011 and 2019. The elevation was measured exclusively with TanDEM-X InSAR data to reduce penetration bias and temporal ambiguities. The geodetic analysis was conducted using a three-module DEM Differencing framework. In this framework, the first module generates high-quality InSAR DEM with an iterative approach to address the challenges of mountainous terrain for InSAR processing; the second module employed an innovative voids filling method using Gaussian Process Regression for robust elevation change mapping; and the third module incorporates a non-stationary uncertainty analysis for rigorous uncertainty quantification. The results reveal a regional mean elevation change rate of $0.0038\pm 0.0042m{\mathrm{yr}}^{-1}$ and a specific mass balance of $0.0032\pm 0.0052m\mathrm{w.e.}{\mathrm{yr}}^{-1}$, indicating slight overall thickening during the study period. The spatial patterns of elevation change display pronounced heterogeneity and clear differences between surge-type and non-surge glaciers, reflecting the complex interplay of dynamic, climatic, and morphological factors in the region. This study demonstrates the capability of high-resolution TanDME-X InSAR DEM for accurate geodetic mass balance analysis in challenging mountain environments. The proposed framework provides a scalable methodology for future large-scale glacier studies.