Streamflow trends in Europe: evidence from a dataset of near-natural catchments

Streamflow observations from near-natural catch- ments are of paramount importance for detection and at- tribution studies, evaluation of large-scale model simula- tions, 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 coun- tries 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 mag- nitude 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 po- tential 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, grad- ually spreading across Europe to reach a maximum extent