RENOIR
Resolving the thickness of debris on Earth’s glaciers and its rate of change.
About the project
Rock debris partially covers glaciers worldwide, with varying extents and distributions, and controls sub-debris melt rates by modifying energy transfer from the atmosphere to the ice. These debris-covered glaciers are common in many mountain ranges, including High-Mountain Asia, the European Alps, the Andes, the Alaska Range and New Zealand’s Southern Alps and understanding how these glaciers evolve is critical as debris-covered glaciers are projected to increase with climate warming.
The main aim of the project is to provide an accurate, high resolution estimate of supraglacial debris thickness for all glaciers on Earth, determine the rate of debris thickness change in climatically and geologically diverse settings, and assess the effect of surface debris on 21st Century glacier change at catchment and global scales. To achieve this, we compiled a database of debris thickness and physical properties from previously published studies, supplemented by fieldwork conducted at various sites worldwide, including (so far) Chile, Switzerland, and Tajikistan. This dataset will play a critical role in developing a remote sensing methodology for mapping supraglacial debris thickness and its associated uncertainty, applicable from the catchment scale to the global scale. We will validate this methodology using high-quality ground-truth data collected from these field sites. The resulting methodology will enable the production of accurate, global estimates of supraglacial debris thickness and the first robust assessments of debris thickness changes. These outputs will be integrated into glacier models to evaluate their impact on glacier melt, mass balance, and future glacier runoff trends in both the catchment and regional scale.
What have we found?
DebDab: A database of supraglacial debris thickness and physical properties –
We compiled a database of measured and reported physical properties and thickness of supraglacial debris, named DebDab. This openly available dataset is designed to evolve and be updated with community submissions as new data on supraglacial properties become available. DebDab includes data on debris thickness, sub-debris ablation rates, thermal conductivity, aerodynamic surface roughness length, albedo, emissivity, and porosity. The dataset spans 83 glaciers across 13 regions in the Global Terrestrial Network for Glaciers. DebDab is a valuable resource for energy balance, melt, and surface mass balance studies by incorporating site-specific debris properties or evaluating remote sensing estimates of debris thickness and surface roughness. It can also guide future field campaigns on debris-covered glaciers by highlighting observation gaps. However, its uneven spatial coverage reflects sampling biases in current community efforts to study debris-covered glaciers.
Inferring Debris Properties on Debris-Covered Glaciers –
Debris on glaciers affects how quickly the underlying ice melts by controlling heat transfer from the air to the ice. Key properties, such as thermal conductivity (k) and surface roughness (z0), are rarely measured directly and are often taken from other studies. Accurate representation of these properties in energy-balance models is crucial for understanding glacier-climate interactions. In our study on Pirámide Glacier (Chile), we compared and evaluated how sub-debris melt is modelled using k and z0 values derived from various previously published methods. We found substantial differences between methods, often leading to mismatches between modelled and observed ice melt. These discrepancies reveal a significant knowledge gap, as field-derived k and z0 values often fail to align with the bulk properties required by energy-balance models.
