Christian Huggel

Glacier retreat is reshaping water availability in tropical mountain catchments, with direct consequences for water-dependent economic activities. This study quantifies the economic losses attributable specifically to glacier retreat in the hydropower and irrigation sectors of the Santa River Basin (Peru) for two future horizons (2040–2050 and 2090–2100) under three climate and socioeconomic scenarios (SSP1-2.6, SSP3-7.0, SSP5-8.5).We combine a lumped hydrological model that explicitly represents glacier melt with an economic assessment of irrigated agriculture and hydropower production. To isolate the effect of glacier retreat from concurrent climate and socioeconomic changes, we apply a three-stage framework: (i) simulation of historical conditions (1981–2020) to calibrate and validate hydrology and define a baseline (2010–2020); (ii) future simulations driven by climate and socioeconomic scenarios with glacier extent fixed at baseline conditions; and (iii) future simulations including scenario-consistent glacier retreat. Economic losses due to glacier retreat are derived from the difference between stages (ii) and (iii). Agriculture losses are estimated from crop-specific water–production relationships for the main crops in the Ancash region, while hydropower losses are assessed for the Cañón del Pato plant based on flow-dependent turbine operation and electricity prices. Environmental flow requirements are included in the study.Results show that glacier retreat reduces runoff in all months and scenarios, with the strongest impacts during the dry season. By mid-century, glacier retreat alone increases economic losses by ~8% in agriculture and ~15% in hydropower relative to futures without glacier change; by the end of the century these increases reach ~15% and ~30%, respectively. Averaged across scenarios, glacier retreat generates additional losses of about USD 170 million by 2050 and USD 360 million by 2100. Losses are highly scenario-dependent: under SSP5-8.5, mid-century losses are comparable to late-century losses under SSP1-2.6, highlighting the accelerating economic costs of high-emission pathways.Our findings demonstrate that glacier retreat is not a marginal hydrological signal but a major economic driver in glacier-fed basins, with implications for long-term water and development planning.

In late May 2025, a series of large rock failures from Kleines Nesthorn in the Swiss Lötschental (Lötschen valley) fell directly onto the Birchgletscher (Birch Glacier), loading the latter with around 4 million m3 of rock. On May 28, following several days of acceleration, Birchgletscher collapsed in its entirety, claiming one life and causing the near-total destruction of the historic village of Blatten (which at this point was completely evacuated). Totaling more than 9 million m3 of rock and glacier ice (with a ratio of about 3:1), the rock-ice avalanche dammed the river Lonza and led to the formation of a lake that damaged additional parts of the village.To reconstruct and understand the physical processes that controlled this remarkable hazard cascade, we used aerial topographic surveys, radar and time-lapse images, direct field observations, eyewitness accounts, meteorological data, and numerical modeling. From these data we 1) determined the precise chronology of the event, including the failure and deposition volumes and geomorphologic event traces; 2) reconstructed the pre-event (1946-2023) history of Kleines Nesthorn and Birchgletscher, including the substantial mass loss of the latter and its recent surge-type acceleration; 3) analyzed the kinematics of the rock instability on Kleines Nesthorn and the resulting rock failures that loaded the glacier; 4) used the 3-D finite element model Elmer/Ice to reconstruct the effect of the rock loading on the force balance of Birchgletscher and its relevance for the observed acceleration and collapse; and 5) processed data from several long-term weather stations, satellite data and climate models to evaluate the relevance of human-caused climate change on Birchgletscher, snow-cover, permafrost and the entire process chain. Our results highlight the complexity of the Nesthorn-Birchgletscher hazard cascade and provide valuable insights for the assessment and management of glacier-related hazards in high mountains.

High mountain environments often experience hazards that do not occur in isolation but as interconnected processes. A typical setting may involve a steep rock face, sometimes topped by glacier ice, where failures can trigger rock-ice or mixed avalanches depending on seasonal conditions. When such events occur above a glacial lake, as is common in many regions, the impact can initiate secondary processes such as glacial lake outburst floods, with significant downstream consequences.Numerical models are valuable tools for estimating the runout of individual processes; however, simulating entire hazard cascades involving multiple material types remains challenging—particularly for forward modeling. In this study, we explore methods for modeling cascading processes, either through integrated physical models or suites of specialized models, and assess which approaches are most suitable at different spatial scales (local, basin, regional, national).At least two GLOFs in the recent five years in Nepal were caused by a cascade of a mass flow impacting the lake and causing dam failure or overtopping, followed by a downstream flood with significant impacts. Permafrost thaw induced slope instability as well as excessive snow melt in source areas contributed to the initial release and a variety of subsequent erosional processes further downstream exacerbated impacts. Previous modelling has been largely focused on the flood from the lake exit, not considering the multiple aspects contributing to the complexity of the cascade.Our analysis focuses on the Thame area in the Everest region of Nepal, where a rock-ice avalanche impacted Thyanbo Lake in August 2024, triggering a glacial lake outburst flood that caused severe damage downstream. This is done in light of producing risk maps for the wider Dudh Kosi Basin, where a number of upstream processes can potentially exacerbate impacts for communities much lower than the periglacial terrain. We discuss the advantages and limitations of various modeling strategies, the challenges of representing full process chains, and potential ways to combine approaches to improve physical realism and predictive capability.

The mountain cryosphere is rapidly changing in the 21st century. Glacier mass loss is accelerating, permafrost is thawing, and precipitation falls increasingly as rain. These are fundamental changes to the hydrological functioning of high mountain catchments, including throughput and storage. There has been focused attention on the progressive development of large glacial lakes, due to their high visibility and impacts in the case of an outburst flood. Satellite-based monitoring of such sites is a relatively straightforward task, yet effective evaluation and early warning of hazards remains challenging, as it must take into account site specific considerations, the possible chains of geomorphic processes, and implementation challenges for technical, logistical, and community ownership aspects. In recent years, however, outburst floods have increasingly occurred originating not from known large proglacial lakes, but from glacial and periglacial lakes that have developed on subseasonal timescales of weeks to months. The development of water bodies over these short timescales is often entirely unnoticed before a flood; as a result, these events have caused significant damage and fatalities, as evidenced in at least 8 distinct events in 2025. Early detection of these emergent water bodies is essential and requires a rapid-repeat operational tool that is reliable and insensitive to meteorological conditions.In this work we develop a framework for rapid identification of anomalous water bodies using Sentinel-1 GRD data in Google Earth Engine. Sentinel-1 is frequently used in inundation mapping efforts due to the low radar backscatter of water, its cloud penetration, and short temporal revisit (6 days for 1A and 1B combined). However, the SAR data present specific challenges: distinct ascending and descending view geometries, difficulties in geocoding due to mountain terrain and glacier thinning, an uncertain backscatter threshold for lake detection, and confounding signals of wet snow, soil moisture, or seasonal vegetation development. Rather than attempting to map lakes directly, we overcome these challenges by instead identifying domains with an anomalous signal that is also consistent with water. Specifically, we determine the anomaly of the latest backscatter data to historic backscatter phenology in each pixel, expressed as a composite z-score for the ascending and descending orbits, and mapped only in domains where radar backscatter and topographic slope are both low. We implement this approach in our tool THAW (Transient Hydrologic Anomalies Weekly) and demonstrate its operational utility by examining the detections that would have occurred preceding the Purepu (Tibet/Nepal) and Rawoshan (Pakistan) events in 2025. In both cases, THAW identified an anomalous signal likely to indicate surface water weeks and months prior to the lakes’ drainage. The approach is not sensitive to seasonally wet snow, as it accounts for the location’s typical seasonality, but highlights the early seasonal melt of Himalayan snowpacks in 2025. Our tests at Purepu identified the growth of another lake at Nyanang Phu (Tibet), enabling an early in-situ assessment by authorities. We find this framework to complement operational lake monitoring workflows by highlighting selected domains of rapid change for expert evaluation.

The last ca. 10 years have seen a particularly strong proliferation of research around glacier lake outburst floods (GLOF), with the number of corresponding peer-reviewed publications hitting 100 per year most recently.Major progress has been made, and debates have developed, around the number, volume and change of glacial lakes, and the frequency of GLOF’s over time and the relation to glacier shrinkage and climate change, globally and in particular regions such as High Mountain Asia. Hazard and risk assessments have been performed widely, ranging from local to global scale, and against a range of climatic and socio-economic future scenarios. Major GLOF events and disasters such as the 2023 South Lhonak GLOF, have been carefully analyzed with an objective to better understand physical processes and impacts. GLOF’s are increasingly sketched as cascading processes, and thus posing important challenges to process understanding, modeling and forecast. A range of models have been applied to GLOF processes, from physically based models for local scale to simpler models at regional scale but important challenges remain.Against this impressive progress in GLOF research, we identify and discuss here critical fields that have not yet received sufficient attention but have important scientific or societal relevance, or represent research areas where progress is facing important challenges and barriers. Specifically, we identify four core frontiers in GLOF research and risk management:(1) Location and dynamics of hazard sources: recent cases have shown that GLOF’s often originate from poorly or unknown, or rapidly changing sources, thus posing a major issue for comprehensive hazard and risk analysis.(2) Probability of occurrence of GLOF’s and GLOF-triggering mass movements such as rock / ice avalanches. Limited research has addressed this issue, and if, typically remained at a qualitative level. Quantification, however, will prove to be essential for areas such as climate litigation cases, for advancing probabilistic hazard and risk assessments, and as a basis for establishing risk transfer mechanisms like insurances.(3) Several events have shown the eminent importance of sediment entrainment and flow dynamics for the impact of GLOF’s on population and infrastructure, but many challenges remain in terms of process understanding, modelling and assessment methods.(4) Effectiveness of risk management and climate change adaptation for GLOFs: quite a range of disaster risk reduction measures for GLOF’s are recognized and global experiences have been recently comprehensively analyzed. However, as we further move into a rapidly changing high-mountain landscape, and public finance is increasingly stressed, the assessment of effectiveness and limits of risk management option against different levels of warming and related GLOF scenarios becomes more and more urgent.We will elaborate how GLOF research can address these frontiers and what it may entail in terms of international cooperation.

Disaster risk management (DRM) for glacial lake outburst floods (GLOFs) is critical due to the increasing risk posed by GLOFs to downstream communities and infrastructure. However, the effectiveness of DRM measures remains insufficiently understood, which hinders effective and target-oriented decision-making in GLOF DRM. Existing research predominantly focuses on hazard aspects, with few scientific studies modelling the impacts of DRM measures comprehensively. In order to fill this gap, this study assesses the effectiveness of three different DRM measures for GLOFs in the Ala-Archa catchment, Kyrgyz Republic. Using numerical modelling, we map and assess the effect of three DRM measures: lake lowering, a deflection dam, and a retention basin and compare it to the current baseline hazard map. We develop a hazard reduction score for comparison of the measures and evaluate their effectiveness based on cost and benefit considerations. This study proposes a conceptual framework and methodology that can guide the management of GLOF and debris flow risks in similar contexts globally.

Aufgrund des Klimawandels sind bewohnte Gebiete zunehmend durch Naturgefahren bedroht. In der Schweiz führen Naturgefahren wie Steinschlag, Murgänge, Lawinen oder Überschwemmungen in seltenen Fällen zu Umsiedlungen, was soziale, finanzielle und rechtliche Herausforderungen mit sich bringt. Dieser Beitrag erarbeitet auf Grundlage von historischen und aktuellen Umsiedlungen im Zusammenhang mit Naturgefahren in der Schweiz einen Leitfaden für den Entscheidungsprozess für geeignete Massnahmen. Dieser berücksichtigt soziale, finanzielle, rechtliche und risikobezogene Aspekte und unterstützt Entscheidungsträgerinnen und -träger dabei, Umsiedlungen als gleichwertige Option zu anderen Massnahmen zu prüfen und an lokale Gegebenheiten anzupassen.

Disaster risk management (DRM) for glacial lake outburst floods (GLOFs) is critical due to the increasing risk posed by GLOFs to downstream communities and infrastructure. However, the effectiveness of DRM measures remains insufficiently understood, which hinders effective and target-oriented decision-making in GLOF DRM. Existing research predominantly focuses on hazard aspects, with few scientific studies modelling the impacts of DRM measures comprehensively. In order to fill this gap, this study assesses the effectiveness of three different DRM measures for GLOFs in the Ala-Archa catchment, Kyrgyz Republic. Using numerical modelling, we map and assess the effect of three DRM measures: lake lowering, a deflection dam, and a retention basin and compare it to the current baseline hazard map. We develop a hazard reduction score for comparison of the measures and evaluate their effectiveness based on cost and benefit considerations. This study proposes a conceptual framework and methodology that can guide the management of GLOF and debris flow risks in similar contexts globally.

Disaster risk management (DRM) for glacial lake outburst floods (GLOFs) is critical due to the increasing risk posed by GLOFs to downstream communities and infrastructure. However, the effectiveness of DRM measures remains insufficiently understood, which hinders effective and target-oriented decision-making in GLOF DRM. Existing research predominantly focuses on hazard aspects, with few scientific studies modelling the impacts of DRM measures comprehensively. In order to fill this gap, this study assesses the effectiveness of three different DRM measures for GLOFs in the Ala-Archa catchment, Kyrgyz Republic. Using numerical modelling, we map and assess the effect of three DRM measures: lake lowering, a deflection dam, and a retention basin and compare it to the current baseline hazard map. We develop a hazard reduction score for comparison of the measures and evaluate their effectiveness based on cost and benefit considerations. This study proposes a conceptual framework and methodology that can guide the management of GLOF and debris flow risks in similar contexts globally.