Effect of glaciers on streamflow trends in the Swiss Alps

Journal of Hydrology

Statistical classification of hydrograph form is used to elucidate the controls on diurnal runoff cycle evolution at Haut Glacier d'Arolla, Switzerland during the 1998 and 1999 melt seasons. Hydrographs are objectively grouped using statistical techniques into four ...

Remote Sensing

Glacier mass variations are climate indicators. Therefore, it is essential to examine both winter and summer mass balance variability over a long period of time to address climate-related ice mass fluctuations. In this study we analyze glacier mass balance components and hypsometric characteristics with respect to their interactions with local meteorological variables and remote large-scale atmospheric and oceanic patterns. The results show that all selected glaciers have lost their equilibrium condition in recent decades, with persistent negative annual mass balance trends and decreasing accumulation area ratios (AARs), accompanied by increasing air temperatures of ≥+0.45 °C decade−1. The controlling factor of annual mass balance is mainly attributed to summer mass losses, which are correlated with (warming) June to September air temperatures. In addition, the interannual variability of summer and winter mass balances is primarily associated to the Atlantic Multidecadal Oscillation...

Journal of Hydrology, 2005

Mean daily streamflow records from 48 watersheds in Switzerland with an undisturbed runoff regime are analysed for trends with the Mann-Kendall nonparametric test in three study periods (). The statistical significance of trends is tested for each station on an annual and seasonal basis and for different streamflow quantiles. The field significance of trends is tested by a bootstrap procedure. Identified trends in streamflow are examined together with changes in precipitation and air temperature, and correlated with watershed attributes. Complex changes in the streamflow regime in Switzerland especially in the more recent periods are demonstrated. The main identified trends are an increase in annual runoff due to increases in the winter, spring and autumn season runoff, an increase in winter maximum streamflow (at more than 60% of the stations) and an increase in spring and autumn moderate and low flows. The behaviour in the summer period is different, with both upward and downward trends present in moderate and low flow quantiles. Many of the trends are field significant. Changes in precipitation are not sufficient to explain the observed trends in streamflow. Air temperature, most notably a substantial increase in the number of days with minimum daily temperature above 0 8C, may explain some of the observed increases in winter and spring season runoff. Correlation analyses reveal a strong relationship between streamflow trends and mean basin elevation, glacier and rock coverage (positive), and basin mean soil depth (negative). These relationships suggest that the most vulnerable environments from the point of view of streamflow change are mountain basins. q

Theoretical and Applied Climatology, 2003

In many instances, snow cover and duration are a major controlling factor on a range of environmental systems in mountain regions. When assessing the impacts of climatic change on mountain ecosystems and river basins whose origin lie in the Alps, one of the key controls on such systems will reside in changes in snow amount and duration. At present, regional climate models or statistical downscaling techniques, which are the principal methods applied to the derivation of climatic variables in a future, changing climate, do not provide adequate information at the scales required for investigations in which snow is playing a major role. A study has thus been undertaken on the behavior of snow in the Swiss Alps, in particular the duration of the seasonal snow-pack, on the basis of observational data from a number of Swiss climatological stations. It is seen that there is a distinct link between snow-cover duration and height (i.e., temperature), and that this link has a specific ''signature'' according to the type of winter. Milder winters are associated with higher precipitation levels than colder winters, but with more solid precipitation at elevations exceeding 1,700-2,000 m above sea-level, and more liquid precipitation below. These results can be combined within a single diagram, linking winter minimum temperature, winter precipitation, and snow-cover duration. The resulting contour surfaces can then be used to assess the manner in which the length of the snow-season may change according to specified shifts in temperature and precipitation. While the technique is clearly empirical, it can be combined with regional climate model information to provide a useful estimate of the length of the snow season with snow cover, for various climate-impacts studies.

Global warming has strong impacts on snow cover, which in turn affects ecosystems, hydrological regimes and winter tourism. Only a few long-term snow series are available worldwide, especially at high elevation. Here, we analyzed several snowpack characteristics over the period 1970–2015 at eleven meteorological stations, spanning elevations from 1139 to 2540 m asl in the Swiss Alps. Snow cover duration has significantly shortened at all sites, on average by 8.9 days decade −1. This shortening was largely driven by earlier snowmelt (on average 5.8 days decade −1) and partly by later snow onset but the latter was significant in only ~30 % of the stations. On average, the snow season now starts 12 days later and ends 26 days earlier than in 1970. Overall, the annual maximum snow depth has declined from 3.9 to 10.6 % decade −1 and was reached 7.8 ± 0.4 to 12.0 ± 0.4 days decade −1 earlier, though these trends hide a high inter-annual and decadal variability. The number of days with snow on the ground has also significantly decreased at all elevations, in all regions and for all thresholds from 1 to 100 cm. Overall, our results demonstrate a marked decline in all snowpack parameters, irrespective of elevation and region, and whether for drier or wetter locations, with a pronounced shift of the snowmelt in spring, in connection with reinforced warming during this season.

International Journal of Climatology, 2013

We present a climate analysis of nine unique Swiss Alpine new snow series that have been newly digitized. The stations cover different altitudes (450-1860 m asl) and all time series cover more than 100 years (one from 1864 to 2009). In addition, data from 71 stations for the last 50-80 years for new snow and snow depth are analysed to get a more complete picture of the Swiss Alpine snow variability. Important snow climate indicators such as new snow sums (NSS), maximum new snow (MAXNS) and days with snowfall (DWSF) are calculated and variability and trends analysed. Series of days with snow pack (DWSP) ≥ 1 cm are reconstructed with useful quality for six stations using the daily new snow, local temperature and precipitation data. Our results reveal large decadal variability with phases of low and high values for NSS, DWSF and DWSP. For most stations NSS, DWSF and DWSP show the lowest values recorded and unprecedented negative trends in the late 1980s and 1990s. For MAXNS, however, no clear trends and smaller decadal variability are found but very large MAXNS values (>60 cm) are missing since the year 2000. The fraction of NSS and DWSP in different seasons (autumn, winter and spring) has changed only slightly over the ∼150 year record. Some decreases most likely attributable to temperature changes in the last 50 years are found for spring, especially for NSS at low stations. Both the NSS and DWSP snow indicators show a trend reversal in most recent years (since 2000), especially at low and medium altitudes. This is consistent with the recent 'plateauing' (i.e. slight relative decrease) of mean winter temperature in Switzerland and illustrates how important decadal variability is in understanding the trends in key snow indicators.

Geographica Helvetica, 2013

Changes in Switzerland's climate are expected to have major impacts on glaciers, the hydrological regime and the natural hazard potential in mountainous regions. Glacier de la Plaine Morte is the largest plateau glacier in the European Alps and thus represents a particularly interesting site for studying rapid and far-reaching effects of atmospheric warming on Alpine glaciers. Based on detailed field observations combined with numerical modelling, the changes in total ice volume of Glacier de la Plaine Morte since the 1950s and the dynamics of present glacier mass loss are assessed. Future ice melt and changes in glacier runoff are computed using climate scenarios, and a possible increase in the natural hazard potential of glacier-dammed lakes around Plaine Morte over the next decades is discussed. This article provides an integrative view of the past, current and future retreat of an extraordinary Swiss glacier and emphasizes the implications of climate change on Alpine glaciers.

Annals of Glaciology

Damage due to glacier floods in the Swiss Alps occurs about once every two years at present, despite the pronounced retreat of glaciers during the twentieth century and the installation of many water reservoirs, which act as flood retention basins. Over half (60 to 70%) of the observed floods are caused by outbursts of marginal glacier lakes or sudden breaks of ice dams, and 30 to 40% by ruptures of water pockets. In a glacierized mountain region as densely populated as the Swiss Alps, even debris flows triggered by outbursts of very small water masses may be dangerous. Historical information about glacier floods in the Swiss Alps, although incomplete and heterogeneous, is used as an empirical basis for an attempt to recognize potential hazards at an early stage by considering outburst processes, volumes of water involved, potential peak-discharge values, lithology and inclination within the reach of glacier streams.

Hydrological Sciences Journal, 2011

The runoff regime of glacierized headwater catchments in the Alps is essentially characterized by snow and ice melt. High Alpine drainage basins influence distant downstream catchments of the Rhine River basin. In particular, during the summer months, low-flow conditions are probable with strongly reduced snow and ice melt under climate change conditions. This study attempts to quantify present and future contributions from snow and ice melt to summer runoff at different spatial scales. For the small Silvretta catchment (103 km 2 ) in the Swiss Alps, with a glacierization of 7%, the HBV model and the glacio-hydrological model GERM are applied for calculating future runoff based on different regional climate scenarios. We evaluate the importance of snow and ice melt in the runoff regime. Comparison of the models indicates that the HBV model strongly overestimates the future contribution of glacier melt to runoff, as glaciers are considered as static components. Furthermore, we provide estimates of the current meltwater contribution of glaciers for several catchments downstream on the River Rhine during the month of August. Snow and ice melt processes have a significant direct impact on summer runoff, not only for high mountain catchments, but also for large transboundary basins. A future shift in the hydrological regime and the disappearance of glaciers might favour low-flow conditions during summer along the Rhine.

1994

The knowledge of the temporary snow-water equivalent storage term (SWE) is an important prerequisite for the assessment of short-and long-term runoff volumes and water quality aspects. Since SWE measurements are frequently not available, this variable is modelled on the basis of operationally measured meteorological data. For model verification fortnightly measured SWE values are used. The choice of the proper model depends on the aim of the simulation and the input data available: if SWE is the only variable to be modelled and time-series of daily total and new snow depths values are available, then a simple model based on Martinec (1977) employing settling curves for each snowfall event is suggested. If apart from SWE values other variables such as liquid water storage, snow albedo, etc. are to be modelled, and hourly input data are available, the conceptual energy and mass balance approach as presented here is suggested. The following variables, measured in hourly intervals, are used as input: air temperature, precipitation, wind speed, water vapour pressure, global radiation and cloud cover (term readings). This model was originally developed at a research-type station but can now be applied at up to 70 stations of the automatic network (ANETZ) of the Swiss Meteorological Institute (SMI). The modelled values are good estimates of the measured ones in the accumulation as well as in the ablation season.