| dc.description.abstract | For people living in and around glacierized catchments runoff that originates from glaciers and snow is a valuable water resource. Especially in arid/semi-arid mountainous regions and during dry periods runoff derived from glaciers and snow can be the only substantial source of water supply. In the European Alps, where most glacierized catchments are characterized by high runoff conditions during summer and low runoff conditions during winter, dry periods are not so common. The expectation however is that climate will change and dry periods will be more common in summer, since temperature is expected to increase and precipitation is expected to decrease. Moreover climate change is expected to affect glacial evolution and likewise the expectation is that climate change will alter the runoff characteristics of these catchments, which will have serious consequences for the water resources and water management of these catchments. Thus, it is important to know how glacierized catchments respond hydrologically to future climate change.
In order to investigate the hydrological response of Alpine catchments to future climate change the semi-distributed hydrological model ‘HBV Light’ is used to model future runoff for gauging stations Brunau (Ötztaler Ache), Obergurgl (Gurgler Ache) and Vent (Venter Ache), which are located in the Ötztal Alps. To understand the functioning of the model, first a sensitivity analysis is conducted in order to investigate the effect of parameter changes on simulated discharge. Subsequently the model is calibrated, validated and forced by separate and combined glacier and climate scenarios. For glacier scenarios, present, near future, mid future and far future glacial area distributions are used. These glacial area distributions are extracted from a model, which is able to derive future ice thickness, glacial area and volume distributions as a result of climate change. For climate scenarios climate projections of daily precipitation and daily temperature for 1985-2100 are used, which are realizations of an ensemble of three RCM’s (ALADIN, RegCM3 and REMO) based on SRES A1B. These projections are subsequently used in a “delta change approach” on a daily basis for (i) near future, (ii) mid future and (iii) far future, using the meteorological data series of 1983-2012 as reference period. Finally, the results of the HBV Light runs are used to analyse changes in the seasonality of high runoff conditions, absolute changes, relative changes, and peak and low flow characteristics.
The glacier scenarios show a stronger rate of ice-thickness reduction than area reduction until 2040. After 2040 the reduction rate of ice-thickness becomes smaller, while reduction rates of area and volume are predicted to increase. At the end of the 21st century the expectation is that less than 20% of the glacier area and volume of 2006 will be left. Future runoff simulations, under glacier-only scenarios, show a decrease in runoff during summer period with relative decreases up to 45%. Also the expectation is that highest runoff conditions will shift from July to June for the gauging stations Obergurgl and Brunau. For climate-only scenarios future runoff simulations show an increase in spring runoff up to 300%. For combined scenarios (glacier and climate change) increases up to 125% for spring and decreases up to 55% for July-August are projected. The highest runoff conditions are expected to shift from July to May-June. The changing runoff conditions may implicate that flood risk will increase during late spring and early summer and therefore result in changing flood seasonality. Moreover low flow conditions will become more frequent during summer months towards the end of the 21st century. These predictions are however uncertain due to uncertainties in meteorological data, glacial evolution, climate projections and model-related aspects, such as parameter uncertainties.
The results of this study help to better understand the future impact of climate change and the associated reduction of glacier volumes on the water cycle of alpine catchments. It may contribute to the development of adaptation measures, reducing the impact of changing runoff characteristics and improving the sustainability of alpine catchments. | |
