AlpWISE : ALPine Water, Ice, Sediment and Ecology

Hydrological modeling in alpine catchments poses unique challenges due to the complex interplay of meteorological, topographical, geological, and glaciological drivers with streamflow generation. A significant issue arises from the limited availability of streamflow data due to the scarcity of high-elevation gauging stations. Consequently, there is a pressing need to assess whether streamflow models that are calibrated with moderate-elevation streamflow data can be effectively transferred to higher-elevation catchments, notwithstanding differences in the relative importance of different streamflow-generation processes. Here, we investigate the spatial transferability of calibrated temperature-index melt model parameters within a semi-lumped modeling framework. We focus on evaluating the melt model transferability from the main catchment to nested and neighboring subcatchments in the Arolla valley, southwestern Swiss Alps. We use the Hydrobricks modeling framework to simulate streamflow, implementing three variants of a temperature-index snow and ice melt model (the classical degree-day model, the aspect-related model, and the Hock temperature-index model). Through an analysis of streamflow simulations, benchmark metrics consisting of resampled and bootstrapped discharge time series, and model performance metrics, we demonstrate that robust parameter transferability and accurate streamflow simulation are possible across diverse spatial scales. This finding is conditional upon the melt model applied, with melt models using more spatial information leading to convergence of the model parameters until we observe overparameterization. We conclude that simple semi-lumped models can be used to extend hydrological simulations to ungauged catchments in alpine regions and improve high-elevation water resource management and planning efforts, especially in the context of climate change. A copy of the paper is freely available here.

Tree rings are valuable proxies for reconstructing changes in climate at annual and intra-annual resolutions. In Alpine regions, changes in climate may well lead to switches between tree-growth being temperature-limited and precipitation-limited. Distinguishing between these is important as they may express themselves differently in tree rings. However, such switches cannot be separated from more local environmental influences such as elevation and aspect. In this study, we seek to understand how tree growth evolves as a function of elevation in the context of climate change. For the growth of European larch (Larix decidua Mill) in the Turtmann River Basin, a glacier-fed high-elevation river basin in the Swiss Alps, located in southwestern Switzerland, we find that the average temperature increase leads to a switch from temperature-limitation to precipitation-limitation as a function of elevation. The growth of Larix decidua Mill in this river basin is influenced by previous year’s September-October-November (SON) temperature and current year’s January-February-March (JFM) precipitation in the higher- and lower-elevations across an elevational gradient respectively. Based on the analysis from four sites, assuming a linear response, our study suggests that there is a transition zone (i.e., an elevational breakpoint) between 1800 and 900 m AMSL where the signal changes from precipitation-limited to temperature-limited. We also conclude that this elevation breakpoint appears to be rising with time due to increasingly warmer annual average temperatures in this Alpine setting, where this warming is noted to be more than twice compared to the global average temperature change. A copy of the paper is freely available here.

Despite ongoing debates about its origins, the Anthropocene—a new epoch characterized by significant human impact on the Earth’s geology and ecosystems—is widely acknowledged. Our environment is increasingly a product of interacting biophysical and social forces, shaped by climate change, colonial legacies, gender norms, hydrological processes, and more. Understanding these intricate interactions requires a mixed-methods approach that combines qualitative and quantitative, biophysical and social research.

However, mixed-methods environmental research remains rare, hindered by academic boundaries, limited training, and the challenges of interdisciplinary collaboration. Time, funding, and the integration of diverse data further complicate this research, whilst the dynamics and ethics of interdisciplinary teams add another layer of complexity.

Despite these challenges, mixed-methods research offers a more robust and ultimately transformative understanding of environmental questions. This Field Guide aims to inspire and equip researchers to undertake such studies. Organized like a recipe book, it assists researchers in the preparation of their field work, as well as offering entry points to key methods and providing examples of successful mixed-methods projects.

This book will be of interest to scholars wishing to tackle environmental research in a more holistic manner, spanning ‘sister’ disciplines such as anthropology, statistics, political science, public health, archaeology, geography, history, ecology, and Earth science.

The book is Open Access and so freely available here.

On 3 October 2023, a multihazard cascade in the Sikkim Himalaya, India, was triggered by 14.7 million m³ of frozen lateral moraine collapsing into South Lhonak Lake, generating an ~20 m tsunami-like impact wave, breaching the moraine, and draining ~50 million m³ of water. The ensuing Glacial Lake Outburst Flood (GLOF) eroded ~270 million m³ of sediment, which overwhelmed infrastructure, including hydropower installations along the Teesta River. The physical scale and human and economic impact of this event prompts urgent reflection on the role of climate change and human activities in exacerbating such disasters. Insights into multihazard evolution are pivotal for informing policy development, enhancing Early Warning Systems (EWS), and spurring paradigm shifts in GLOF risk management strategies in the Himalaya and other mountain environments.

A copy of the paper is freely available here.

Glacio-hydrological models are widely used for estimating current and future streamflow across spatial scales, utilizing various data sources, notably observed streamflow and snow and/or ice accumulation, as well as ablation observations. However, modelling highly glacierized catchments poses challenges due to data scarcity and complex spatio-temporal meteorological conditions, leading to input data uncertainty and potential misestimation of the contribution of snow and ice melt to streamflow. Some studies propose using water stable isotopes to estimate shares of rain, snow and ice in streamflow, yet the choice of the isotopic composition of these water sources significantly impacts results.

This study presents a combined isotopic and glacio-hydrological model which provides catchment-integrated snow and ice melt isotopic compositions during an entire melting season. These isotopic compositions are then used to estimate the seasonal shares of snow and ice melt in streamflow for the Otemma catchment in the Swiss Alps. The model leverages available meteorological station data (air temperature, precipitation and radiation), ice mass balance data and snow cover maps to model and automatically calibrate the catchment-scale snow and ice mass balances. The isotopic module, building on prior work by Ala-Aho et al. (2017a), estimates seasonal isotopic compositions of precipitation, snow and ice. The runoff generation and transfer module relies on a combined routing and reservoir approach and is calibrated based on measured streamflow and isotopic data.

Results reveal challenges in distinguishing snow and ice melt isotopic values in summer, rendering a reliable separation between the two sources difficult. The modelling of catchment-wide snowmelt isotopic composition proves challenging due to uncertainties in precipitation lapse rate, mass exchanges during rain-on-snow events and snow fractionation. The study delves into these processes and their impact on model results and suggests guidelines for future models. It concludes that water stable isotopes alone cannot reliably separate snow and ice melt shares for temperate alpine glaciers. However, combining isotopes with glacio-hydrological modelling enhances hydrologic parameter identifiability, in particular those related to runoff transfer to the stream, and improves mass balance estimations.

A copy of the paper is freely available here.

Investigating erosion and river sediment yield in high-mountain areas is crucial for understanding landscape and biogeochemical responses to environmental change. We compile data on contemporary fluvial suspended sediment yield (SSY) and 12 environmental proxies from 151 rivers in High Mountain Asia surrounding the Tibetan Plateau. We demonstrate that glaciers exert a first-order control on fluvial SSYs, with high precipitation nonlinearly amplifying their role, especially in high–glacier cover basins. We find a bidirectional response to vegetation’s influence on SSY in the Eastern Tibetan Plateau and Tien Shan and identify that the two interacting factors of precipitation and vegetation cover explain 54% of the variability in SSY, reflecting the divergent roles of vegetation in promoting biogenic-weathering versus slope stabilization across bioclimatic zones. The competing interactions between glaciers, ecosystems, and climate in delivering suspended sediment have important implications for predicting carbon and nutrient exports and water quality in response to future climate change. A copy is freely available here.

Proglacial forefields commonly include highly dynamic fluvial systems associated with the fundamental instability between topography, flow hydraulics and sediment transport. However, there is limited knowledge of how these systems respond to changing subglacial hydrology and sediment supply. We investigated this relationship using the first continuous field-collected data sets for both suspended and bedload sediment export and proglacial river dynamics for an Alpine glacier forefield, the Glacier d’Otemma, Switzerland. The results show a strong sensitivity of fluvial morphodynamics to the balance between sediment transport capacity and supply. When subglacial bedload export rates exceeded fluvial transport capacity, we found bar construction leading to net forefield aggradation and surficial coarsening, especially on bar heads. This intensified braiding buffered the downstream transport of coarse sediment. When subglacial bedload export rates were lower than transport capacity, incision occurred, with reduced braiding intensity, net erosion and important amounts of bedload leaving the proglacial system. We found a net fining of surficial deposits except for very isolated coarsening patterns on bar heads. Thus, proglacial forefield morphodynamics are strongly conditioned by subglacial hydrology and sediment supply, but this conditioning is also influenced by the response of the forefield itself. Proglacial forefields have an important influence on the longitudinal connectivity of sediment flux in regions sensitive to climate change, such as recently deglaciated high mountain areas. The linkages we report between subglacial processes and river morphodynamics are critical for understanding the development of embryonic forefield ecosystems. A copy of the paper is freely available here.

Measurement of river bathymetry has been revolutionized by high-resolution remote sensing that combines UAV platforms with SfM-MVS photogrammetry. Mapping inundated and exposed areas simultaneously are possible using either two-media refraction correction or some form of the Beer–Lambert Law to estimate water depths. If, as in turbid glacially-fed braided streams, the bed is not visible then traditional survey techniques (e.g. differential GPS systems) are required. As an alternative, here we test whether the spatial distribution of water depths in a shallow braided stream can be modelled from basic planimetric data and used to estimate inundated zone bathymetry. We develop heuristic rules using; (1) distance from the nearest river bank; (2) total inundated width along a line tangential to the local flow direction; (3) local curvature magnitude and direction; and distance from the nearest flow (4) divergence and (5) convergence regions. We parameterize them using a sample of measured water depths in stepwise multiple linear regressions and validate them using independent data. Resulting water depth distribution maps explain between 50% and 60% of the measured water depth spatial variability when compared to independent data. After incorporating modelled water depths into digital elevation models (DEMs) of exposed areas, we show that the developed method is suitable for volumetric change calculations in both dry and inundated areas. A copy is freely available here.

Glaciers in Afghanistan are crucial elements for water resource and summer river flows. They are also threatened by rapid climate warming. This study presents an up-to-date assessment of ice cover loss for the entire country over two periods, 2000–2008 and 2008–2020, using newly developed remote sensing indices that include a more reliable determination of changing debris cover. The results suggest an estimated ice-covered area of 2,690.7 ± 108.2 km² in 2020, that was 75 ± 0.7% clean ice and 25 ± 3.0 percent debris-covered ice. Total ice-covered area retreated by −0.16 ± 0.01 percent yr⁻¹ between 2000 and 2008 and −0.46 ± 0.05 percent yr⁻¹ between 2008 and 2020. Notably, 60 percent of ice cover loss (2000–2020) related to ice cover extents with a size ≤ 2.5 km², comprising 60 percent of the total ice-covered area in 2000. Higher altitude accumulation zones also exhibited mass loss. However, there was also substantial spatial variation in these rates of loss based on geographical region, glacier size, and climate zones. In the north-eastern regions that are geographically close to or part of the north-west Karakoram ice cover was declining at a substantially lower rate, stable, or even increasing slightly, as compared with the northern and central regions of Afghanistan. A copy is freely available here.

Emergency responders in coastal cities are anticipated to provide effective evacuation of at-risk populations during the preparedness and response phases of coastal floods due to land-falling storms or cyclones. However, existing contingency plans primarily focus on the evacuation of the general public rather than special arrangement for elderly populations who constitute a large proportion of flood fatalities. Here we present a system-level methodology to elaborate citywide coastal flood evacuation plans for optimal deployment of shelters and effective transfer of elderly people with special needs. We conduct a comparative analysis between Shanghai and New York City, which are both among the most exposed coastal cities to storm-induced flooding but represent two distinct institutional systems of emergency operation. The results show marked disparities in evacuation patterns for elderly residents in the two cities. Storm flood evacuation is more challenging in Shanghai due to insufficient provision of shelter capacity (~230,000). Implementing risk-informed and strategic planning could not only meet the potentially huge demand of vulnerable elderly (~520,000) but also improve the overall efficiency of evacuee transfer by a factor of 3. Our work provides new insights into operational emergency evacuation decisions and informs flood management policy development for major coastal cities globally. A copy is available here.