Exploring contemporaneous observational datasets to derive glacier surface mass balance from continuity approaches (ContinuIX working group)

The surface mass balance (SMB) of glaciers represents a direct link to the local climate and is a key variable in modelling glacier response to climate change. While the SMB is traditionally measured at point locations with ablation stakes or snowpits, recent advances allow estimation of spatially distributed SMB using remotely sensed data of surface elevation change, ice velocity, and ice thickness by solving the mass continuity equation. Such inverse approaches offer a promising alternative to field-based SMB data collection, particularly for model calibration and large-scale assessments. However, SMB inversion approaches vary in spatial coverage, assumptions, and solution strategies as well as in using data of different resolutions and temporal consistency—raising questions about their comparability, performance, and uncertainties.

The Continuity approaches for mass balance Intercomparison eXercise (ContinuIX) is a community effort organized through an IACS Working Group that aims to compare existing continuity approaches for SMB estimation and to deliver clear guidelines and recommendations for future developers and users of SMB products derived from these methods. The first objective of ContinuIX focuses on compiling a benchmark dataset with high-quality, contemporaneous observational data (surface elevation change, velocity, thickness, and in situ SMB), as well as controlled synthetic test cases. The next activities will involve a structured intercomparison experiment using these best possible datasets to assess differences between approaches.

Here, we present progress on the benchmark dataset of phase one, which includes extensive contemporaneous observations of eight glaciers across multiple regions. This dataset may be of value for a wide range of glaciological studies. Additionally, we apply and present first results of mass continuity methods to demonstrate how distributed SMB products can be derived, providing a preview of the types of comparisons envisioned for the next objective of ContinuIX. This presentation is intended not only to share initial results, but also to invite input and discussion from the community as we shape the next steps of ContinuIX. We particularly welcome ideas, feedback, and expressions of interest from potential contributors or users of continuity-derived SMB products.