Steps towards consistent production of Rock Glacier Velocity (RGV): comparison and assessment of challenges from three technical approaches

Rock glaciers are prevalent debris landforms associated with periglacial terrain and formed by the creep of mountain permafrost. In recent years, there has been increasing interest in the dynamics and evolution of rock glaciers under climate change. Research indicates a general acceleration of creep rates, as well as an increasing incidence of rock glacier destabilization and degradation. Recently, the Rock Glacier Inventories and Kinematics (RGIK) initiative achieved the inclusion of the Rock Glacier Velocity (RGV) as an additional product of the Essential Climate Variable (ECV) for permafrost in the Global Climate Observing System (GCOS). Likewise, the RGIK initiative, and particularly the RGV Working Group, have been developing baseline and practical concepts on how to define and produce RGV. In parallel, the ESA Permafrost Climate Change Initiative (CCI) and the SwissUniversities Open Rock Glacier Data Production Tools (ORoDaPT) project have been working on the development of tools and datasets for RGV monitoring. In order to test and validate these concepts, an intercomparison exercise was performed by several operators grouped into three technical subgroups, depending on the data and techniques used to produce RGV: in-situ measurements, optical photogrammetry, and radar remote sensing. The groups worked on three distinct sites in the European Alps (Gran Sometta – Italy, Grosses Gufer – Switzerland and Laurichard – France) with consistent input data provided for each technique. Each operator generated RGV time series for each site using their individual methodological expertise and adjusted their workflows to agree with the generic RGV production rules defined in the guidelines. Emphasis was placed on comparing results within the groups and in-between the different techniques. This contribution summarizes the major results of this so-called 2024 RGV intercomparison workshop. It focuses on concepts, methods and recommendations for producing consistent RGV products. While the list of proposed rock glaciers and methods is not exhaustive and is still a work in progress, our goal here is to provide a starting point for the RGIK Working Group on RGV, as well as for the wider rock glacier and permafrost communities, in terms of documenting best practices for RGV generation, including examples of possible challenges along with practical solutions.