Present and future impact of snow cover and glaciers on runoff from mountain regions

The aim of this contribution is to show how snow- and glaciermelt influence runoff today and in the future under the assumption that global warming continues. This assumption will not necessarily come into effect, but according to climatologists, the opposite is rather unlikely in the next few hundred years, for example a drastic cooling due to changes in ocean currents. Mountain regions receive more precipitation than the lowlands around them, and act as a reservoir of this excess water by temporarily storing it in the form of snow and ice. Melt is highest during warm and dry periods and thus runoff increases during times of drought. This release from snow and ice storage ensures a reliable water flow in rivers, and thus is of great value in terms of irrigation and other water uses. Glaciers, therefore, influence the water cycle very favourably by collecting water during times of abundance and releasing it when there is a lack of precipitation. Even in a warmer climate we expect precipitation to fall abundantly in the mountains, but more and more in the form of rain rather than snow, and therefore the character of runoff will change from a glacial or nival regime towards a pluvial one. This will produce a less reliable water yield and the absence of glaciers will lead to water shortages during hot and dry summers, when water is needed most urgently for irrigation and drinking water. Therefore, we need to develop strategies to adapt to the situation that rivers will run dry more often in the future

Digitale Aufbereitung historischer Gletscherkarten in Bayern

Bei der Diskussion über die globale Erwärmung wird immer wieder auf die Bedeutung der Gletscher als Klimaindikatoren und Wasserspeicher verwiesen (IPCC 2001; UNEP 1992). In diesem Zusammenhang werden meist die wenigen großen Gletscher der Alpen als Beispiele angeführt. Dabei reagieren kleine Gletscher viel schneller auf Klimaschwankungen und stellen zudem durch ihre zahlenmäßige Überlegenheit einen nicht unerheblichen Teil der alpinen Eisreserven. Die fünf bayerischen Gletscher bieten sich für Zwecke der Langzeitbeobachtung (engl. Monitoring) besonders an, da sie bereits seit 1889 in unregelmäßigen Abständen vermessen wurden. Allerdings wurden die Daten bisher nur teilweise ausgewertet und liegen zudem auf unterschiedlichen Medien und in verschiedenen Maßstäben und Koordinatensystemen vor. Ein Hauptziel des von der Deutschen Forschungsgemeinschaft geförderten Projekts „Bayerische Gletscher“, das an der Sektion Geographie der LMU München in enger Kooperation mit der Kommission für Glaziologie der Bayerischen Akademie der Wissenschaften bearbeitet wird, ist die Digitalisierung und Homogenisierung der bestehenden Daten sowie ihre Veröffentlichung in der Internet-Datenbank www.bayerische-gletscher.de

Glacier changes in the Bavarian Alps from 1989/90 to 2006/07

The five glaciers in Bavaria which today cover a total area of less than one square kilometer were frequently monitored by geodetic methods from the mid of the 20th century. In this paper, the record is extended by new surveys in 1999 and 2006. The glaciers show a prolonged surface lowering, which is intensified compared to the 1980s and reaches maximum rates from 1999-2006. Moreover, the ice thickness of four glaciers was determined in 2006 and 2007 by geophysical field techniques and allows the calculation of ice volumes. First simple extrapolations of observed volume losses indicate that the two Berchtesgaden glaciers and Südlicher Schneeferner could disappear by 2016, while the ice of Nördlicher Schneeferner endures until 2027. Ice thicknesses and surface changes are visualized in five annexed maps.Die fünf bayerischen Gletscher, die heute insgesamt eine Fläche von weniger als einem Quadratkilometer bedecken, wurden seit der Mitte des 20. Jahrhunderts regelmäßig geodätisch aufgenommen. Diese Reihe wird hier um zwei Neuvermessungen in den Jahren 1999 und 2006 erweitert. Alle Gletscher zeigen in dem Zeitraum eine fortgesetzte Erniedrigung ihrer Oberfläche, die im Vergleich zu den 1980er Jahren verstärkt ist und in der Periode 1999-2006 Maximalwerte aufzeigt. Außerdem wurden in den Jahren 2006 und 2007 die Eisdicken von vier Gletschern durch geophysikalische Messungen bestimmt, was erstmalig die Ermittlung des verbleibenden Eisvolumens erlaubt. Erste einfache Extrapolationen der beobachteten Volumenverluste in die Zukunft deuten an, dass die beiden Gletscher in den Berchtesgadener Alpen sowie der Südliche Schneeferner bis zum Jahr 2016 verschwinden könnten, während der Nördliche Schneeferner noch bis 2027 überdauern würde. Eisdicken und Oberflächenänderungen werden anhand von fünf Karten im Anhang verdeutlicht

Sub-debris melt rates on southern Inylchek Glacier, central Tian Shan

Melt rates of glacier surfaces are strongly influenced by the existence of a debris cover. Dependent on thickness and other physical parameters the debris layer can enhance or reduce ablation as compared to bare ice conditions. Supraglacial moraines appear very frequently on Central Asian glaciers, highly affecting water yield from these high mountain regions. In summer 2005, a network of 22 ablation stakes was drilled into locations with varying debris thicknesses on Southern Inylchek glacier in the central Tian Shan. Mean ablation rates varied from 2.8 to 6.7 cm/d, strongly correlated with moraine thickness. Parallel observation of air temperature allowed the application of a simple degree-day approach and the calculation of ablation rates. Efforts to improve calculations of melt rates by incorporating relative air humidity to account for latent heat fluxes failed. This proves that air temperature is already a very good melt indicator. Ice albedo measurements show that reflectivity might be controlled by the occurrence of evaporation or condensation, but this topic needs further investigation

Glacial debris cover and melt water production for glaciers in the Altay, Russia

Glaciers are important water storages on a seasonal and long-term time scale. Where high mountains are surrounded by arid lowlands, glacier runoff is an important source of water during the growing season. This situation can be found in the Altay mountains in Southern Siberia, where the recent glacierization of >700 km2 is subject to continuous mass loss, even though the shrinking is comparably slow. The glacier retreat is accompanied by an extension of supra-glacial moraine, which itself strongly influences ablation rates. To quantify these effects, the spatial evolution of debris cover since 1952 was analysed for three glaciers in the North Chuya Ridge using satellite and airborne imagery. In summer 2007, an ablation experiment was carried out on debris covered parts of Maliy Aktru glacier. Thermistors in different depths within the moraine provided data to calculate thermal resistance of the debris. A set of ablation stakes was installed at locations with differing debris thickness and observed regularly throughout the entire melt season. Air temperature from an AWS was used to calculate degree day factors in dependence of the debris thickness. To take into account the shading effect of surrounding walls and peaks, the potential solar radiation and its evolution throughout the summer was determined from a digital elevation model. This allows us to extrapolate our measurements from Maliy Aktru to the other two glaciers of the Aktru basin and to estimate basin melt rates. In addition accumulated ice melt was derived for 12 glaciers in the North Chuya Range. Changes in summer runoff from the 1960s are compared to the results from our melt model and the evolution of debris cover is analysed in respect to the melt activity

Runoff modelling in glacierized Central Asian catchments for present-day and future climate

A conceptual precipitation–runoff model was applied in five glacierized catchments in Central Asia. The model, which was first developed and applied in the Alps, works on a daily time step and yields good results in the more continental climate of the Tien Shan mountains for present-day climate conditions. Runoff scenarios for different climates (doubling of CO2) and glacierization conditions predict an increased flood risk as a first stage and a more complex picture after a complete glacier loss: a higher discharge during spring due to an earlier and more intense snowmelt is followed by a water deficiency in hot and dry summer periods. This unfavourable seasonal redistribution of the water supply has dramatic consequences for the Central Asian lowlands, which depend to a high degree on the glacier melt water for irrigation and already nowadays suffer from water shortages

Glaciological results of the 2005 expedition to Inylchek Glacier, Central Tian Shan

Like many other glaciers in Central Asia, Southern Inylchek glacier in the Kyrgyz Tian Shan is covered by supraglacial moraine, which drastically influences melt rates and complicates the estimation of ablation. The quantification of sub-debris melt from simple parameters is still an unsolved problem, but also essential to predict future yield from high mountains. Snow cover and glacier ice are the main water storages for the surrounding arid lowlands and a better understanding of ablation processes is the prerequisite for a sustainable water resources management. Another interesting feature of Southern Inylchek glacier is the existence of an ice dammed lake in a tributary valley, which is drained regularly by outburst floods. Improvements in predicting these floods would lower the risk potential for the downstream population. The main objectives of a group of glaciologists which participated in an expedition to the glacier in 2005 were to investigate melt rates on debris covered glacier parts and to quantify the ice flux into the glacier lake. The results of their field experiments are reported in this paper

Modelling of hydrological response to climate change in glacierized Central Asian catchments

The arid lowlands of Central Asia are highly dependent on the water supplied by the Tien Shan mountains. Snow and ice storage make large contributions to current runoff, particularly in summer. Two runoff models with different temporal resolutions, HBV-ETH and OEZ, were applied in three glaciated catchments of the Tien Shan mountains. Scenario runs were produced for a climate change caused by the doubling of atmospheric CO2 as predicted by the GISS global circulation model and assuming a 50% reduction of glaciation extent, as well as a complete loss of glaciation. Agreement of the results was best for runs based on 50% glaciation loss, where both models predict an increase in spring and summer runoff compared to current levels. Scenarios for complete loss of glaciation predict an increase in spring runoff levels, followed by lower runoff levels for July and August. Model predictions differ concerning the degree of reduction of late summer runoff. These scenarios are sensitive to model simulation of basin precipitation, as well as to reduction of glaciation extent