Trends in flow intermittence for European rivers

Intermittent rivers are prevalent in many countries across Europe, but little is known about the temporal evolution of intermittence and its relationship with climate variability. Trend analysis of the annual and seasonal number of zero-flow days, the maximum duration of dry spells and the mean date of the zero-flow events is performed on a database of 452 rivers with varying degrees of intermittence between 1970 and 2010. The relationships between flow intermittence and climate are investigated using the standardized precipitation evapotranspiration index (SPEI) and climate indices describing large-scale atmospheric circulation. The results indicate a strong spatial variability of the seasonal patterns of intermittence and the annual and seasonal number of zero-flow days, highlighting the controls exerted by local catchment properties. Most of the detected trends indicate an increasing number of zero-flow days, which also tend to occur earlier in the year, particularly in southern Europe. The SPEI is found to be strongly related to the annual and seasonal zero-flow day occurrence in more than half of the stations for different accumulation times between 12 and 24 months. Conversely, there is a weaker dependence of river intermittence with large-scale circulation indices. Overall, these results suggest increased water stress in intermittent rivers that may affect their biota and biochemistry and also reduce available water resources.This research is part of the COST action CA15113 SMIRES, Science and Management of Intermittent Rivers and Ephemeral Streams https://www.smires.eu/, a short-term scientific mission that has been funded for Agnieszka Rutkowska. Agnieszka Rutkowska was also supported by the Ministry of Science and Higher Education of the Republic of Poland (grant DS 3371). The different data providers are gratefully acknowledged. Some of the station data were retrieved from the Global Runoff Data Centre (56068 Koblenz, Germany) and from the HyMeX programme database. The authors would like to thank two anonymous reviewers, Kendra Kaiser and the Associate Editor, Stephanie Kampf, for their constructive comments.Peer reviewe