Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Hydrol. Earth Syst. Sci., 20, 3967-3985, 2016
https://doi.org/10.5194/hess-20-3967-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
27 Sep 2016
A three-pillar approach to assessing climate impacts on low flows
Gregor Laaha1, Juraj Parajka2, Alberto Viglione2, Daniel Koffler1, Klaus Haslinger3, Wolfgang Schöner4, Judith Zehetgruber1, and Günter Blöschl2 1Institute of Applied Statistics and Computing, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria
2Institute for Hydraulic and Water Resources Engineering, Vienna University of Technology, Vienna, Austria
3Climate Research Department, Central Institute for Meteorology and Geodynamics, Vienna, Austria
4Department of Geography and Regional Science, University of Graz, Graz, Austria
Abstract. The objective of this paper is to present a framework for assessing climate impacts on future low flows that combines different sources of information, termed pillars. To illustrate the framework three pillars are chosen: (a) extrapolation of observed low-flow trends into the future, (b) rainfall–runoff projections based on climate scenarios and (c) extrapolation of changing stochastic rainfall characteristics into the future combined with rainfall–runoff modelling. Alternative pillars could be included in the overall framework. The three pillars are combined by expert judgement based on a synoptic view of data, model outputs and process reasoning. The consistency/inconsistency between the pillars is considered an indicator of the certainty/uncertainty of the projections. The viability of the framework is illustrated for four example catchments from Austria that represent typical climate conditions in central Europe. In the Alpine region where winter low flows dominate, trend projections and climate scenarios yield consistently increasing low flows, although of different magnitudes. In the region north of the Alps, consistently small changes are projected by all methods. In the regions in the south and south-east, more pronounced and mostly decreasing trends are projected but there is disagreement in the magnitudes of the projected changes. The process reasons for the consistencies/inconsistencies are discussed. For an Alpine region such as Austria the key to understanding low flows is whether they are controlled by freezing and snowmelt processes, or by the summer moisture deficit associated with evaporation. It is argued that the three-pillar approach offers a systematic framework of combining different sources of information aimed at more robust projections than that obtained from each pillar alone.

Citation: Laaha, G., Parajka, J., Viglione, A., Koffler, D., Haslinger, K., Schöner, W., Zehetgruber, J., and Blöschl, G.: A three-pillar approach to assessing climate impacts on low flows, Hydrol. Earth Syst. Sci., 20, 3967-3985, https://doi.org/10.5194/hess-20-3967-2016, 2016.
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Short summary
We present a framework for assessing climate impacts on future low flows that combines different sources of information termed pillars. To illustrate the framework, three pillars are chosen: low-flow observation, climate observations and climate projections. By combining different sources of information we aim at more robust projections than obtained from each pillar alone. The viability of the framework is illustrated for four example catchments from Austria.
We present a framework for assessing climate impacts on future low flows that combines different...
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