Author: Stuart Lane

Outburst floods triggered by breaching of landslide dams may cause severe loss of life and property downstream. Accurate identification and assessment of such floods, especially when leading to secondary impacts, are critical. In 2018, the Baige landslide in the Tibetan Plateau twice blocked the Jinsha River, eventually resulting in a severe outburst flood. The Baige landslide remains active, and it is possible that a breach happens again. Based on numerical simulation using a hydrodynamic model, remote sensing, and field investigation, we reproduce the outburst flood process and assess the hazard associated with future floods. The results show that the hydrodynamic model could accurately simulate the outburst flood process, with overall accuracy and Kappa accuracy for the flood extent of 0.956 and 0.911. Three future dam break scenarios were considered with landslide dams of heights 30 m, 35 m, and 51 m. The potential storage capacity and length of upstream flow back up in the upstream valley for these heights were 142 × 10⁶m³/32 km, 182 × 10⁶m³/40 km, and 331 × 10⁶m³/50 km. Failure of these three dams leads to maximum inundation extents of 0.18 km², 0.34 km², and 0.43 km², which is significant out-of-bank flow and serious infrastructure impacts. These results demonstrate the seriousness of secondary hazards associated with this region. A copy is freely available here.

The rapid recession of glaciers is exposing large zones to the development of embryonic phototrophic ecosystems and eventual ecological succession. Traditionally, succession patterns in glacial forefields have been seen as a response to time since deglaciation, but nowadays forefield exposure is so rapid that this theory may be less applicable. In this succession process, periphyton are potential pioneer organisms because of their role in modifying the local environment (e.g. access to water) to create conditions conducive to plant colonization. In this paper, we aimto decrypt the physical properties of the habitats that define the spatial and temporal assemblage of periphyton during the melt-season of an Alpine temperate glacier in the context of rapid climate change. We show that periphyton develop in glacial floodplains throughout the melt-season and could extend to cover significant surfaces. However, development is only possible when the combined conditions of stability and water accessibility are met. In glacial floodplains, stable zones exist and are typically located on terraces; but they can also be locally found for much shorter periods in the more active, glacial-stream reworked zone. On terraces, water accessibility can be a limit due to well-drained sediments, but when present, often aided by the role that biofilms play in creating an impermeable layer, it provides a stable and clear water source that biofilms could exploit. In the active part of the braid plain, whilst water availability is very high, the water is harsh (low temperature, high turbidity) and erosive. Therein, periphyton can rapidly exploit short windows of opportunity but the habitat conditions rarely remain stable for long enough for continuous periphyton cover to develop. Thus, the role of periphyton in ecosystem succession is strongly conditioned by the spatial extent of the active zone, itself a function of high rates of glacier melt and sediment supply associated with rapid glacier retreat. A copy of the paper is freely available here.

Proglacial margins form when glaciers retreat and create zones with distinctive ecological, geomorphological and hydrological properties in Alpine environments. There is extensive literature on the geomorphology and sediment transport in such areas as well as on glacial hydrology, but there is much less research into the specific hydrological behavior of the landforms that develop after glacier retreat in and close to proglacial margins. Recent reviews have highlighted the presence of groundwater stores even in such rapidly draining environments. Here, we describe the hydrological functioning of different superficial landforms within and around the proglacial margin of the Otemma glacier, a temperate Alpine glacier in the Swiss Alps; we characterize the timing and amount of the transmission of different water sources (rain, snowmelt, ice melt) to the landforms and between them, and we compare the relationship between these processes and the catchment-scale discharge. The latter is based upon a recession-analysis-based framework. In quantifying the relative groundwater storage volumes of different superficial landforms, we show that steep zones only store water on the timescale of days, while flatter areas maintain baseflow on the order of several weeks. These landforms themselves fail to explain the catchment-scale recession patterns; our results point towards the presence of an unidentified storage compartment on the order of 40 mm, which releases water during the cold months. We suggest attributing this missing storage to deeper bedrock flowpaths. Finally, the key insights gained here into the interplay of different landforms as well as the proposed analysis framework are readily transferable to other similar proglacial margins and should contribute to a better understanding of the future hydrogeological behavior of such catchments. A copy is freely available here.

The Swiss plate geophone (SPG) system has been installed and tested in more than 20 steep gravel-bed streams and rivers, and related studies generally resulted in rather robust calibration relations between signal impulse counts and transported bedload mass. Here, we compare this system with three alternative surrogate measuring systems. A variant of the SPG system uses the same frame (housing) set-up but with an accelerometer instead of a geophone sensor to measure the vibrations of the plate (GP-Acc, for geophone plate accelerometer). The miniplate accelerometer (MPA) system has a smaller dimension of the impact plate and is embedded in more elastomer material than the SPG system. The Japanese pipe microphone (JPM) is a 1 m long version of the system that has been installed in many streams in Japan. To compare the performance of the four systems, we used calibration measurements with direct bedload samples from three field sites and an outdoor flume facility with controlled sediment feed. At our field sites, the systems with an accelerometer and a microphone showed partly large temporal variations in the background noise level, which may have impaired the calibration measurements obtained during certain time periods. Excluding these periods, the SPG, GP-Acc, and JPM all resulted in robust calibration relations, whereas the calibration of the MPA system showed a poorer performance at all sites. A copy is freely available here.

Rapid atmospheric warming since the mid-twentieth century has increased temperature-dependent erosion and sediment-transport processes in cold environments, affecting food, energy and water security. In this Review, we summarize landscape changes in cold environments and provide a global inventory of increases in erosion and sediment yield driven by cryosphere degradation. Anthropogenic climate change, deglaciation, and thermokarst disturbances are causing increased sediment mobilization and transport processes in glacierized and periglacierized basins. With continuous cryosphere degradation, sediment transport will continue to increase until reaching a maximum (peak sediment). Thereafter, transport is likely to shift from a temperature-dependent regime toward a rainfall-dependent regime roughly between 2100–2200. The timing of the regime shift would be regulated by changes in meltwater, erosive rainfall and landscape erodibility, and complicated by geomorphic feedbacks and connectivity. Further progress in integrating multisource sediment observations, developing physics-based sediment-transport models, and enhancing interdisciplinary and international scientific collaboration is needed to predict sediment dynamics in a warming world. A copy of the paper published in Nature – Earth and Environment can be obtained by emailing Stuart Lane (stuart.lane@unil.ch).

ALTROCLIMA is a three-year project funded jointly by the Swiss National Science Foundation and the Autonomous Province of the South Tyrol (Italy). It will support two PhD students based at the University of Lausanne, Switzerland, and a research assistant and a post-doctoral researcher at the Free University of Bozen-Bolzano, Italy (Professor Francesco Comiti, and involves a number of project partners in Switzerland and Italy.

Project aims and objectives

Alpine landscapes are experiencing climate warming at rates higher than other regions of the world. Globally, impacts of warming on the cryosphere are evident in all mountain regions including permafrost degradation; rates of mass movement (rockfalls, debris flows, landslides) at higher altitudes; river flows; and terrestrial/ aquatic ecosystems. Predictions of changing snow/ice cover are available to the end of the 21^st century and there are attempts to couple climate change to river flow in Alpine landscapes including correct treatment of the cryosphere. How bedload transport will evolve under these drivers is much less well-established despite the important environmental significance of bedload for the ecological functioning of Alpine streams and for its potential hazard to Alpine communities. There are only a few decadal-scale records of bedload transport in mountain basins and almost no studies coupling such records to changing river basin function, historically or in terms of predictions. Such analysis must consider the balance between climate-driven changes in bedload supply (S) and bedload transport capacity (C); but also the feedbacks that follow when SC, such as sediment sorting processes when S<C. It is challenging because bedload transport is exceptionally difficult to measure and globally, unlike other measures of environmental change, we have very few instrumented sites worldwide for bedload transport monitoring extending to more than a decade of observations.

Aims and objectives:  The core aim of this project is to understand and to predict how rapid climate warming has and will impact bedload transport in Alpine environments at the centennial timescale. The objectives are;  O1 to provide the first reliable, multi-site quantification in Alpine environments of how bedload transport is changing under warming; O2 to determine the relative role of landscape-scale processes in driving estimated bedload export in the analyzed basins; O3 to establish an appropriate modelling framework for predicting glacier and hillslope bedload supply to the river network using evidence from O1 and O2; O4 to calibrate and to validate of a predictive model for representing bedload flux through the drainage network supported by data from O3; and O5 to provide the first predictions of Alpine bedload transport under future climate considering changes in both supply and capacity.

Methods: Using an innovative method for analyzing the bedload flushing records provided by high altitude Alpine water intakes we will reconstruct bedload export for more than 60 Alpine basins with varying glacier cover for the Swiss Alps and South Tyrol (O1). We will combine these within-basin reconstructed erosion and deposition patterns and connectivity analyses to explain the changes found in O1 (O2). Using results from O2 we will identify and test against O1 the relative merits of stochastic and physically-based models of subglacial and hillslope bedload delivery to the river network (O3). We will integrate these models to generate network-scale predictions of bedload transport under climate change with relative uncertainty (O4).

Expected results and impact: The research will produce the first decadal-scale multi-site quantification of how bedload transport has changed in Alpine environments due to climate warming and why. It will provide the first predictions with uncertainty of how Alpine bedload transport might evolve under 21^st century climate change. The associated understanding and predictions will not only be of academic value but also of importance for water resource managers (including hydropower companies and national/local flood mitigation agencies) in Alpine regions.

AlpWISE is a partner in a new MCSA doctoral training network, EnvSeis. Details of the network are available here. This is part of the EU Horizon 2020 programme. Switzerland is currently excluded from the programme but has adopted transitional measures, including direct Swiss government funding, to allow Swiss scientists to collaborate. So, we have a new grant starting. We will be leading on the project concerned with Seismic sensing of subglacial to proglacial marginal sediment flux and also collaborating on many of the other projects. We are particularly keen to look at subglacial seismic sediment transport monitoring. The grant will allow us to hire a PhD student.

Part 1 : Model invalidation is a good thing. It means that we are forced to reconsider either model structures or the available data more closely, that is to challenge our fundamental understanding of the problem at hand. It is not easy, however, to decide when a model should be invalidated, when we expect that the sources of uncertainty in environmental modelling will often be epistemic rather than simply aleatory in nature. In particular, epistemic errors in model inputs may well exert a very strong control over how accurate we might expect model predictions to be when compared against evaluation data that might also be subject to epistemic uncertainties. We suggest that both modellers and referees should treat model validation as a form of Turing-like Test, whilst being more explicit about how the uncertainties in observed data and their impacts are assessed. Eight principles in formulating such tests are presented. Being explicit about the decisions made in framing an analysis is one important way to facilitate communication with users of model outputs, especially when it is intended to use a model simulator as a ‘model of everywhere’ or ‘digital twin’ of a catchment system. An example application of the concepts is provided in Part 2.

Part 2 :

Part 1 of this study discussed the concept of using a form of Turing-like Test for model evaluation, together with eight principles for implementing such an approach. In this part, the framing of fitness-for-purpose as a Turing-like Test is discussed, together with an example application of trying to assess whether a rainfall-runoff model might be an adequate representation of the discharge response in a catchment for predicting future natural flood management scenarios. It is shown that the variation between event runoff coefficients in the record can be used to create some limits of acceptability that implicitly take some account of the epistemic uncertainties arising from lack of knowledge about errors in rainfall and discharge observations. In the case study it is demonstrated that the model used cannot be validated in this way across all the range of observed discharges, but that behavioural models can be found for the peak flows that are the subject of interest in the application. Thinking in terms of the Turing-like Test focusses attention on the critical observations needed to test whether streamflow is being produced in the right way so that a model is considered as fit-for-purpose in predicting the impacts of future change scenarios. As is the case for uncertainty estimation in general, it is argued that the assumptions made in setting
behavioural limits of acceptability should be stated explicitly to leave an audit trail in any application that can be reviewed by users of the model outputs.

A copy of Part 1 can be obtained here and Part 2 here

Substantial uncertainties in bedload transport predictions in steep streams have encouraged intensive efforts towards the development of surrogate monitoring technologies. One such system, the Swiss plate geophone (SPG), has been deployed and calibrated in numerous steep channels, mainly in the Alps. Calibration relationships linking the signal recorded by the SPG system to the intensity and characteristics of transported bedload can vary substantially between different monitoring stations, likely due to site-specific factors such as flow velocity and bed roughness. Furthermore, recent flume experiments on the SPG system have shown that site-specific calibration relationships can be biased by elastic waves resulting from impacts occurring outside the plate boundaries. Motivated by these findings, we present a hybrid calibration procedure derived from flume experiments and an extensive dataset of 308 direct field measurements at four different SPG monitoring stations. Our main goal is to investigate the feasibility of a general, site-independent calibration procedure for inferring fractional bedload transport from the SPG signal. First, we use flume experiments to show that sediment size classes can be distinguished more accurately using a combination of vibrational frequency and amplitude information than by using amplitude information alone. Second, we apply this amplitude–frequency method to field measurements to derive general calibration coefficients for 10 different grain-size fractions. The amplitude– frequency method results in more homogeneous signal responses across all sites and significantly improves the accuracy of fractional sediment flux and grain-size estimates. We attribute the remaining site-to-site discrepancies to large differences in flow velocity and discuss further factors that may influence the accuracy of these bedload estimates. A copy of the paper is freely available here.

Loess landform variability across large spatial extents needs to be analyzed to understand the formation and evolution of loess landscapes. This is becoming increasingly possible via the automated analysis of remotely-sensed data. Here, we quantify loess landforms using an object-based image analysis (OBIA) method and use this classification to describe the spatial variability of loess landforms. Quantitative indicators are used to drive the spatial variability analysis of loess landforms and explain their spatio-temporal evolution. Moreover, the hypsometric integral (HI) and topographic interpolation are employed to investigate soil erosion and development patterns of loess landscape. Results show that the OBIA method classified loess landforms to an accuracy of 88.7 %. The derived metrics in terms of the area, slope and complexity of landform shape allow the determination of the spatial structure of the loess landscapes. The HI value of the entire basin is 0.486, representing the mature stage of landform development, with relatively severe surface erosion. Correlation analysis of HI values and related indicators in the sub-basins shows that HI is poorly correlated with the area proportion  of loess landform types and the total erosion volume in the basin but shows a relatively strong correlation with the volume of erosion per unit area. A link to the paper is here.