Abstract
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 magnitude and timing. A regionally coherent picture of annual streamflow trends emerged, with negative trends in southern and eastern regions, and generally positive trends elsewhere. Trends in monthly streamflow for 1962–2004 elucidated potential causes for these changes, as well as for changes 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 mostly 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.
Highlights
Elucidating regional patterns of hydrological change has become one of the most important challenges in contemporary hydrology
The purpose of this study is to provide an observational account of the evolution of European streamflow through the greater part of the 20th and early 21st centuries, with a particular emphasis on flow regime characteristics relevant for water resources management
The spatial distribution of these trends is distinct (Fig. 1), with negative trends found in two geographical regions: one is the southwest of the domain, i.e. Spain and southern France, and the other is the central to eastern edge of the domain, i.e. parts of Austria and Germany, the Czech Republic, and Slovakia
Summary
Elucidating regional patterns of hydrological change has become one of the most important challenges in contemporary hydrology. Reliable information on such patterns, beyond the river basin or national scale, enables the identification and attribution of changes in flow regimes influenced by largescale processes such as climate change. K. Stahl et al.: Streamflow trends in Europe: evidence from a dataset of near-natural catchments et al, 2009), confounding the identification of climate-driven changes. Hannah et al (2010) emphasize, that data requirements for climate change detection studies are demanding; they should be based on good quality data from observation networks of rivers with near-natural conditions
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