High Alpine Catchments Research Articles

Rocks control the chemical composition of surface water from the high Alpine Zermatt area (Swiss Alps)

The study presents composition data of 87 surface water samples from high alpine catchments of the Zermatt area (Swiss Alps). The investigated area covers 170 km2. It was found that the surface runoff acquires the dissolved solids mostly by reaction of precipitation water with the minerals of the bedrock. Total dissolved solids (TDS) vary from 6 to 268 mg L−1. All collected water shows a clear chemical signature of the bedrock mineralogy. The contribution of atmospheric input is restricted to small amounts of ammonium nitrate and sodium chloride. NH4 is a transient component and has not been detected in the runoff. Evaporation is not a significant mechanism for TDS increase in the Zermatt area. The chemical composition of the three main types of water can be related to the mineralogy of the dominant bedrock in the catchments. Specifically, Ca-HCO3 (CC) waters develop from metamorphic mafic rocks and from carbonate-bearing schists. Mg-HCO3 water originates from serpentinites and peridotites. Ca-SO4 (CS) waters derive from continental basement rocks such as pyrite-rich granite and gneiss containing oligoclase or andesine. The collected data suggest that, together with reaction time, modal sulfide primarily controls and limits TDS of the waters by providing sulfuric acid for calcite (CC waters) and silicate (CS waters) dissolution. If calcite is present in the bedrock, its dissolution neutralizes the acid produced by sulphide weathering and buffers pH to near neutral to weakly alkaline conditions. If calcite is absent, the process produces low-pH waters in gneiss and granite catchments. The type of bedrock and its mineral assemblage can be recognized in water leaving very small catchments of some km2 area. The large variety of water with a characteristic chemical signature is an impressive consequence of the richly diverse geology and the different rock inventory of the local catchments in the Zermatt area.

A methodology for monitoring and modeling of high altitude Alpine catchments

Hydrological monitoring and modeling of high altitude Alpine catchments is of paramount importance. This is difficult, however, given the complex logistics of field campaigns and the need for long-term data. Here, we present a method for long term monitoring of high altitude catchments, which we tested within the Alps of Italy. This includes i) extensive gathering of climate data and hydrological fluxes, ii) high altitude field campaigns, and iii) robust physically based glacio-hydrological modeling, providing full account of ice flow, ice and snow ablation, and stream flows. We present an application of this method based on six years (2009–2014) of field monitoring in the Dosdè catchment, in the Italian Alps (17 km2, average altitude 2858 masl, outlet 2133 masl), nesting 1.90 km2 of glaciers. We demonstrate that i) high altitude Alpine catchments can be monitored in spite of geographical complexity, and ii) a data based approach delivers accurate stream flow estimates and improves our knowledge of flow components in the high altitudes. We then provide some estimates of the recent glaciers’ dynamics, and water resources from this high-altitude catchment, paradigmatic of the recent cryospheric evolution in the Alps of Italy. We estimated an average ice mass loss nearby −1.76E8 m3yr−1, i.e. −20% of the ice mass in 2009, possibly pointing to accelerated glaciers’ down wasting. Instream discharges increased (+0.12 m3s−1y−1); however, this requires further monitoring. We then benchmark our findings against recent studies in the Alps, and other glacierized areas worldwide, displaying similarities in present glaciers’ dynamics. We suggest that our robust, yet flexible approach can be used for glacio-hydrological investigation in Alpine (and generally mountain) rivers, and for conjectures of potential future hydrological cycle under climate scenarios.

Impact of mountain permafrost on flow path and runoff response in a high alpine catchment

AbstractPermafrost in high alpine catchments is expected to disappear in future warmer climates, but the hydrological impact of such changes is poorly understood. This paper investigates the flow paths and the hydrological response in a 5 km2 high alpine catchment in the Ötztal Alps, Austria, and their changes resulting from a loss of permafrost. Spatial permafrost distribution, depth to the permafrost table, and depth to the bedrock were mapped by geophysical methods. Catchment runoff and meteorological variables were monitored from June 2008 to December 2011. These data were used along with field experience to infer conceptual schemes of the dominant flow paths in four types of hillslopes that differ in terms of their unconsolidated sediment characteristics and the presence of permafrost. The four types are: talus fans, rock glaciers, Little Ice Age (LIA) till, and pre‐LIA till. Permafrost tends to occur in the first three types, but is absent from pre‐LIA till. Based on these flow path concepts, runoff was simulated for present conditions and for future conditions when permafrost has completely disappeared. The simulations indicate that complete disappearance of permafrost will reduce flood peaks by up to 17% and increase runoff during recession by up to 19%. It is argued that change modeling needs to account for flow path types and their changes based on geophysical surveys and field investigations.

Constant denudation rates in a high alpine catchment for the last 6 kyrs

AbstractTerrestrial cosmogenic nuclides (TCN) have widely been used as proxies in determining denudation rates in catchments. Most studies were limited to samples from modern active streams, thus little is known about the magnitude and causes of TCN variability on millennial time scales. In this work we present a 6 kyrs long, high resolution record of 10Be concentrations (n = 18), which were measured in sediment cores from an alluvial fan delta at the outlet of the Fedoz Valley in the Swiss Alps. This record is paired with a 3‐year time series (n = 4) of 10Be measured in sediment from the active stream currently feeding this fan delta. The temporal trend in the 10Be concentrations after correction for postdepositional production of 10Be was found to be overall constant and in good agreement with the modern river 10Be concentration. The calculated mean catchment‐wide denudation rate amounts to 0.73 ± 0.18 mm yr−1. This fairly constant level of 10Be concentrations can be caused by a constant denudation rate over time within the catchment or alternatively by a buffered signal. In this contribution we suggest that the large alluvial floodplain in the Fedoz Valley may act as an efficient buffer on Holocene time scales in which sediments with different 10Be signatures are mixed. Therefore, presumable variations in the 10Be signals derived from changes in denudation under a fluctuating Holocene climate are only poorly transferred to the catchment outlet and not recorded in the 10Be record. However, despite the absence of high frequency signals, we propose that the buffered and averaged 10Be signal could be meaningfully and faithfully interpreted in terms of long‐term catchment‐averaged denudation rate. Our study suggests that alluvial buffers play an important role in regulating the 10Be signal exported by some alpine settings that needs to be taken into account and further investigated. Copyright © 2016 John Wiley & Sons, Ltd.

Response of Hydrological Processes to Input Data in High Alpine Catchment: An Assessment of the Yarkant River basin in China

Most studies of input data used in hydrological models have focused on flow; however, point discharge data negligibly reflect deviations in spatial input data. To study the effects of different input data sources on hydrological processes at the catchment scale, eight MIKE SHE models driven by station-based data (SBD) and remote sensing data (RSD) were implemented. The significant influences of input variables on water components were examined using an analysis of the variance model (ANOVA) with the hydrologic catchment response quantified based on different water components. The results suggest that compared with SBD, RSD precipitation resulted in greater differences in snow storage in the different elevation bands and RSD temperatures led to more snowpack areas with thinner depths. These changes in snowpack provided an appropriate interpretation of precipitation and temperature distinctions between RSD and SBD. For potential evapotranspiration (PET), the larger RSD value caused less plant transpiration because parameters were adjusted to satisfy the outflow. At the catchment scale, the spatiotemporal distributions of sensitive water components, which can be defined by the ANOVA model, indicate that this approach is rational for assessing the impacts of input data on hydrological processes.

Flood‐type classification in mountainous catchments using crisp and fuzzy decision trees

AbstractFloods are governed by largely varying processes and thus exhibit various behaviors. Classification of flood events into flood types and the determination of their respective frequency is therefore important for a better understanding and prediction of floods. This study presents a flood classification for identifying flood patterns at a catchment scale by means of a fuzzy decision tree. Hence, events are represented as a spectrum of six main possible flood types that are attributed with their degree of acceptance. Considered types are flash, short rainfall, long rainfall, snow‐melt, rainfall on snow and, in high alpine catchments, glacier‐melt floods. The fuzzy decision tree also makes it possible to acknowledge the uncertainty present in the identification of flood processes and thus allows for more reliable flood class estimates than using a crisp decision tree, which identifies one flood type per event. Based on the data set in nine Swiss mountainous catchments, it was demonstrated that this approach is less sensitive to uncertainties in the classification attributes than the classical crisp approach. These results show that the fuzzy approach bears additional potential for analyses of flood patterns at a catchment scale and thereby it provides more realistic representation of flood processes.

Dependence between flood peaks and volumes: a case study on climate and hydrological controls

The aim of this paper is to understand the causal factors controlling the relationship between flood peaks and volumes in a regional context. A case study is performed based on 330 catchments in Austria ranging from 6 to 500 km2 in size. Maximum annual flood discharges are compared with the associated flood volumes, and the consistency of the peak–volume relationship is quantified by the Spearman rank correlation coefficient. The results indicate that climate-related factors are more important than catchment-related factors in controlling the consistency. Spearman rank correlation coefficients typically range from about 0.2 in the high alpine catchments to about 0.8 in the lowlands. The weak dependence in the high alpine catchments is due to the mix of flood types, including long-duration snowmelt, synoptic floods and flash floods. In the lowlands, the flood durations vary less in a given catchment which is related to the filtering of the distribution of all storms by the catchment response time to produce the distribution of flood producing storms.Editor Z.W. Kundzewicz

Climate change impacts on bedload transport in alpine drainage basins with hydropower exploitation

AbstractSediment transport is known to have a significant impact on hydropower infrastructures and changes in sediment transport rates are important for sediment management measures and hydroelectricity production. In this study, we present how climate change may affect bedload transport in 66 high alpine catchments used by hydropower companies in the Valais, Switzerland. Future sediment yield is estimated with a runoff‐based sediment transport model for the two future 30 year time periods 2021–2050 and 2070–2099. The analysis is integrated into a modelling chain in which error‐corrected and downscaled climate scenarios generated in the framework of the ENSEMBLES project are coupled to the hydrological model PREVAH, glacier retreat and bedload transport. To calibrate the sediment transport model, we used the observed sediment volumes in water intakes and reservoirs if such data were available. The results obtained show on average a decrease of sediment yield due to the reduced runoff generation during summer, especially for the scenario period 2070–2099. A shift of the seasonal sediment transport regime with a current maximum during July and August to earlier months in the year is predicted. Projections of future sediment yield rely on the accuracy of the individual modeling chain elements. The different sources of uncertainty are discussed qualitatively. Copyright © 2015 John Wiley & Sons, Ltd.

Snow depth mapping in high-alpine catchments using digital photogrammetry

Abstract. Information on snow depth and its spatial distribution is crucial for numerous applications in snow and avalanche research as well as in hydrology and ecology. Today, snow depth distributions are usually estimated using point measurements performed by automated weather stations and observers in the field combined with interpolation algorithms. However, these methodologies are not able to capture the high spatial variability of the snow depth distribution present in alpine terrain. Continuous and accurate snow depth mapping has been successfully performed using laser scanning but this method can only cover limited areas and is expensive. We use the airborne ADS80 optoelectronic scanner, acquiring stereo imagery with 0.25 m spatial resolution to derive digital surface models (DSMs) of winter and summer terrains in the neighborhood of Davos, Switzerland. The DSMs are generated using photogrammetric image correlation techniques based on the multispectral nadir and backward-looking sensor data. In order to assess the accuracy of the photogrammetric products, we compare these products with the following independent data sets acquired simultaneously: (a) manually measured snow depth plots; (b) differential Global Navigation Satellite System (dGNSS) points; (c) terrestrial laser scanning (TLS); and (d) ground-penetrating radar (GPR) data sets. We demonstrate that the method presented can be used to map snow depth at 2 m resolution with a vertical depth accuracy of ±30 cm (root mean square error) in the complex topography of the Alps. The snow depth maps presented have an average accuracy that is better than 15 % compared to the average snow depth of 2.2 m over the entire test site.

Response of snow cover and runoff to climate change in high Alpine catchments of Eastern Switzerland

A model study on the impact of climate change on snow cover and runoff has been conducted for the Swiss Canton of Graubünden. The model Alpine3D has been forced with the data from 35 Automatic Weather Stations in order to investigate snow and runoff dynamics for the current climate. The data set has then been modified to reflect climate change as predicted for the 2021–2050 and 2070–2095 periods from an ensemble of regional climate models.The predicted changes in snow cover will be moderate for 2021–2050 and become drastic in the second half of the century. Towards the end of the century the snow cover changes will roughly be equivalent to an elevation shift of 800m. Seasonal snow water equivalents will decrease by one to two thirds and snow seasons will be shortened by five to nine weeks in 2095.Small, higher elevation catchments will show more winter runoff, earlier spring melt peaks and reduced summer runoff. Where glacierized areas exist, the transitional increase in glacier melt will initially offset losses from snow melt. Larger catchments, which reach lower elevations will show much smaller changes since they are already dominated by summer precipitation.

Snow accumulation of a high alpine catchment derived from LiDAR measurements

Abstract. The spatial distribution of snow accumulation substantially affects the seasonal course of water storage and runoff generation in high mountain catchments. Whereas the areal extent of snow cover can be recorded by satellite data, spatial distribution of snow depth and hence snow water equivalent (SWE) is difficult to measure on catchment scale. In this study we present the application of airborne LiDAR (Light Detecting And Ranging) data to extract snow depths and accumulation distribution in an alpine catchment. Airborne LiDAR measurements were performed in a glacierized catchment in the Ötztal Alps at the beginning and the end of three accumulation seasons. The resulting digital elevation models (DEMs) were used to calculate surface elevation changes throughout the winter season. These surface elevation changes were primarily referred to as snow depths and are discussed concerning measured precipitation and the spatial characteristics of the accumulation distribution in glacierized and unglacierized areas. To determine the redistribution of catchment precipitation, snow depths were converted into SWE using a simple regression model. Snow accumulation gradients and snow redistribution were evaluated for 100 m elevation bands. Mean surface elevation changes of the whole catchment ranges from 1.97 m to 2.65 m within the analyzed accumulation seasons. By analyzing the distribution of the snow depths, elevation dependent patterns were obtained as a function of the topography in terms of aspect and slope. The high resolution DEMs show clearly the higher variation of snow depths in rough unglacierized areas compared to snow depths on smooth glacier surfaces. Mean snow depths in glacierized areas are higher than in unglacierized areas. Maximum mean snow depths of 100 m elevation bands are found between 2900 m and 3000 m a.s.l. in unglacierized areas and between 2800 m and 2900 m a.s.l. in glacierized areas, respectively. Calculated accumulation gradients range from 8% to 13% per 100 m elevation band in the observed catchment. Elevation distribution of accumulation calculated by applying these seasonal gradients in comparison to elevation distribution of SWE obtained from airborne laser scanning (ALS) data show the total redistribution of snow from higher to lower elevation bands. Revealing both, information about the spatial distribution of snow depths and hence the volume of the snow pack, ALS data are an important source for extensive snow accumulation measurements in high alpine catchments. These information about the spatial characteristics of snow distribution are crucial for calibrating hydrological models in order to realistically compute temporal runoff generation by snow melt.

Evapotranspiration in high alpine catchments – an important part of the water balance!

In this paper the third water balance component, the actual evapotranspiration (ETA), is analysed. Although evapotranspiration rates decrease with increasing altitude, it can be concluded that substantial quantitative differences are found among temperature and energy balance-based techniques for estimating the ETA. The objective of this study is to apply a distributed and continuous hydrological model and to utilise standard meteorological datasets with a high spatio-temporal resolution (1 km2 and 60 min) to estimate the evapotranspiration in high Alpine Austrian catchments. Compared with the Hargreaves and Thornthwaite methods the ASCE-Penman-Monteith approach yields substantially higher potential evapotranspiration (ETP) rates, with basin-values up to 24% higher compared with the temperature-based methods. The decrease of ETP with elevation ranges from 6 to 26 mm per 100 m. The ETA rates differ up to 15%, with a decrease of 18–28 mm per 100 m. About 30% of the annual precipitation is evaporated and this implies that even larger correction factors of precipitation are required to satisfy the runoff. The method is demonstrated in basins in the north central Austrian Alps.

Altitudinal dependency of snow amounts in two small alpine catchments: can catchment-wide snow amounts be estimated via single snow or precipitation stations?

AbstarctThe spatial distribution and the local amount of snow in mountainous regions strongly depend on the spatial characteristics of snowfall, snow deposition and snow redistribution. Uniform altitudinal gradients can only represent a part of these influences but are without alternative for use in larger-scale models. How well altitudinal gradients represent the true snow distribution has not been assessed. We analyse altitudinal characteristics of snow stored in two high-alpine catchments in Switzerland. Peak winter snow depths were monitored using high-resolution airborne laser scanning technology. These snow depths were transferred to snow water equivalent by applying simple density estimations. From these data, altitudinal gradients were calculated for the total catchment areas and for selected subareas characterized by different accumulation patterns. These gradients were then compared with gradients resulting from automated snow depth measurements obtained from several snow stations on different height levels located in the catchments, and with estimations from climatological precipitation gradients. The analysis showed that neither precipitation gradients nor flat-field stations estimate catchment-wide snow amounts accurately. While the climatological gradient showed different trends for different areas and years, the snow stations tended to overestimate mean snow amounts.

Spatial and temporal variability of snow depth and ablation rates in a small mountain catchment

Abstract. The spatio-temporal variability of the mountain snow cover determines the avalanche danger, snow water storage, permafrost distribution and the local distribution of fauna and flora. Using a new type of terrestrial laser scanner, which is particularly suited for measurements of snow covered surfaces, snow depth was monitored in a high alpine catchment during an ablation period. From these measurements snow water equivalents and ablation rates were calculated. This allowed us for the first time to obtain a high resolution (2.5 m cell size) picture of spatial variability of the snow cover and its temporal development. A very high variability of the snow cover with snow depths between 0–9 m at the end of the accumulation season was observed. This variability decreased during the ablation phase, while the dominant snow deposition features remained intact. The average daily ablation rate was between 15 mm/d snow water equivalent at the beginning of the ablation period and 30 mm/d at the end. The spatial variation of ablation rates increased during the ablation season and could not be explained in a simple manner by geographical or meteorological parameters, which suggests significant lateral energy fluxes contributing to observed melt. It is qualitatively shown that the effect of the lateral energy transport must increase as the fraction of snow free surfaces increases during the ablation period.

Hydrological model performance and parameter estimation in the wavelet-domain

Abstract. This paper proposes a method for rainfall-runoff model calibration and performance analysis in the wavelet-domain by fitting the estimated wavelet-power spectrum (a representation of the time-varying frequency content of a time series) of a simulated discharge series to the one of the corresponding observed time series. As discussed in this paper, calibrating hydrological models so as to reproduce the time-varying frequency content of the observed signal can lead to different results than parameter estimation in the time-domain. Therefore, wavelet-domain parameter estimation has the potential to give new insights into model performance and to reveal model structural deficiencies. We apply the proposed method to synthetic case studies and a real-world discharge modeling case study and discuss how model diagnosis can benefit from an analysis in the wavelet-domain. The results show that for the real-world case study of precipitation – runoff modeling for a high alpine catchment, the calibrated discharge simulation captures the dynamics of the observed time series better than the results obtained through calibration in the time-domain. In addition, the wavelet-domain performance assessment of this case study highlights the frequencies that are not well reproduced by the model, which gives specific indications about how to improve the model structure.

Correlation between climate, man and debris flow events — A palynological approach

Debris flows occur frequently in the high-alpine catchment area of lake Lago di Braies (1492 m a.s.l.). The sediments of the lake are used for detecting and dating past debris flow events during the last 4000 years and their driving factors. Comparing palynological and sedimentological data the results suggest, that mainly heavy precipitation in winter and summer as well as snow melt events in spring enhance the release of debris flow events. Therefore especially longer periods with humid and cool climate conditions show a clearly higher debris flow activity. The pollen diagram documents human impact on the catchment area since the late Neolithic, but the anthropogenic activities influenced the event activity only indirectly. Grazing and deforestation reduced the retention of debris by vegetation and results in thicker debris flow layers in the lake sediments.

Combination of Numerical Dating Techniques Using 10Be in Rock Boulders and 14C of Resilient Soil Organic Matter for Reconstructing the Chronology of Glacial and Periglacial Processes in a High Alpine Catchment during the Late Pleistocene and Early Holocene

Glacier fluctuations and paleoclimatic oscillations during the Late Quaternary in Val di Rabbi (Trentino, northern Italy) were reconstructed using a combination of absolute dating techniques (14C and 10Be) and soil chemical characterization. Extraction and dating of the stable fraction of soil organic matter (SOM) gave valuable information about the minimum age of soil formation and contributed to the deciphering of geomorphic surface dynamics. The comparison of 10Be surface exposure dating (SED) of rock surfaces with the 14C ages of resilient (resistant to H2O2 oxidation) soil organic matter gave a fairly good agreement, but with some questionable aspects. It is concluded that, applied with adequate carefulness, dating of SOM with 14C might be a useful tool in reconstructing landscape history in high Alpine areas with siliceous parent material. The combination of 14C dating of SOM with SED with cosmogenic 10Be (on moraines and erratic boulders) indicated that deglaciation processes in Val di Rabbi were already ongoing by around 14,000 cal BP at an altitude of 2300 m asl and that glacier oscillations might have affected the higher part of the region until about 9000 cal BP. 10Be and 14C ages correlate well with the altitude of the sampling sites and with the established Lateglacial chronology.

A debris flow calendar derived from sediments of lake Lago di Braies (N. Italy)

In this study lake sediments were used for developing a high resolution calendar of past debris flow events. Debris flows frequently occur in the high-alpine catchment of the lake Lago di Braies (N. Italy). While the coarse grained material accumulates on the debris flow cones, the fine grained material is flushed into the lake. This material forms characteristic layers in the lake sediments, which are different from the typical annual lamination. By analysing thin sections of sediment, debris flow events of the last 2250 years were reconstructed with an annual resolution. Since debris flow frequency varies strongly, periods with high and low frequencies can be distinguished. However, neither a debris flow magnitude–frequency relationship nor a strong reaction of debris flow activity to past climate changes was identifiable in this study.

Geocryological processes linked to High Arctic proglacial stream suspended sediment dynamics: examples from Bylot Island, Nunavut, and Spitsbergen, Svalbard

AbstractRecent research has identified differences in processes contributing to suspended sediment concentration (SSC) dynamics in proglacial streams between High Arctic and alpine catchments, but does not examine processes explicitly linked to the periglacial environment. Three glacierized basins were studied: Austre Brøggerbreen and Midre Lovénbreen, Svalbard (79°N, 12°E) and Glacier B28, unofficially named Stagnation Glacier, Bylot Island, Nunavut (73°N, 78°W). SSC variations were modelled from continuous turbidity, discharge and meteorological data throughout the summer months. Three statistical tools were utilized: principal component analysis, change‐point analysis and multivariate regression. These are shown to be effective in identifying subperiods of distinctive geocryological and glaciofluvial characteristics. Multivariate regression for the subseasons included autoregressive integrated moving‐average modelling, and showed that SSC variations were related not only to discharge variability, but also to fluctuations in energy fluxes. The results are interpreted in terms of spatio‐temporal changes in sediment mobilization and supply associated with changes in the relative importance of fluvial, glacial and periglacial processes. This evidence supports the notion of important linkages between glacial, fluvial and periglacial systems, but exemplifies distinct variability between High Arctic glaciers. Copyright © 2005 John Wiley & Sons, Ltd.

Modification of sediment characteristics during glacial transport in high-alpine catchments: Mount Cook area, New Zealand

Modification of sediment characteristics during glacial transport in high-alpine catchments: Mount Cook area, New Zealand