Hydrol. Earth Syst. Sci. Discuss., 7, 5769-5804, 2010
© Author(s) 2010. This work is distributed
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This discussion paper has been under review for the journal Hydrology and Earth System Sciences (HESS). Please refer to the corresponding final paper in HESS.
Streamflow trends in Europe: evidence from a dataset of near-natural catchments
K. Stahl1,2, H. Hisdal3, J. Hannaford4, L. M. Tallaksen1, H. A. J. van Lanen5, E. Sauquet6, S. Demuth7, M. Fendekova8, and J. Jódar9
1Department of Geosciences, University of Oslo, Norway
2Institute of Hydrology, University of Freiburg, Germany
3Norwegian Water Resources and Energy Directorate, Oslo, Norway
4Centre for Ecology and Hydrology, Wallingford, UK
5Hydrology and Quantitative Water Management Group, Centre for Water and Climate, Wageningen University, The Netherlands
6UR Hydrologie-Hydraulique, Cemagref, Lyon, France
7Division of Water Sciences, Section of Hydrological Processes and Climate, Natural Sciences Sector, UNESCO, Paris, France
8Department of Hydrogeology, Faculty of Natural Sciences, Comenius University in Bratislava, Bratislava, Slovakia
9Institute of Environmental Assessment and Water Research (IDAEA-CSIC), Spain

Abstract. Streamflow observations from near-natural catchments are of paramount importance for detection and attribution studies, evaluation of large-scale model simulations, and assessment of water management, adaptation and policy options. This study investigates streamflow trends in a newly-assembled, consolidated dataset of near-natural streamflow records from 441 small catchments in 15 countries across Europe. The period 1962–2004 provided the best spatial coverage, but analyses were also carried out for longer time periods (with fewer stations), starting in 1932, 1942 and 1952. Trends were calculated by the slopes of the Kendall-Theil robust line for standardized annual and monthly streamflow, as well as for summer low flow and low flow timing. A regionally coherent picture of annual streamflow trends emerged, with negative trends in southern and eastern regions, and generally positive trends elsewhere (especially in northern latitudes). Trends in monthly streamflow for 1962–2004 elucidated potential causes for these changes, as well as other changes observed in hydrological regimes across Europe. Positive trends were found in the winter months in most catchments. A marked shift towards negative trends was observed in April, gradually spreading across Europe to reach a maximum extent in August. Low flows have decreased in most regions where the lowest mean monthly flow occurs in summer, but vary for catchments which have flow minima in winter and secondary low flows in summer. The study largely confirms findings from national and regional scale trend analyses, but clearly adds to these by confirming that these tendencies are part of coherent patterns of change, which cover a much larger region. The broad, continental-scale patterns of change are congruent with the hydrological responses expected from future climatic changes, as projected by climate models. The patterns observed could hence provide a valuable benchmark for a number of different studies and model simulations.

Citation: Stahl, K., Hisdal, H., Hannaford, J., Tallaksen, L. M., van Lanen, H. A. J., Sauquet, E., Demuth, S., Fendekova, M., and Jódar, J.: Streamflow trends in Europe: evidence from a dataset of near-natural catchments, Hydrol. Earth Syst. Sci. Discuss., 7, 5769-5804, doi:10.5194/hessd-7-5769-2010, 2010.
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