Abstract
Intermittent rivers are prevalent in many countries across Europe and in Mediterranean countries outside Europe, but little is known about the temporal evolution of intermittency characteristics and their relationships with climate variability. In this study, a trend analysis is performed on the annual and seasonal number of zero-flow days, the maximum duration of dry spells and the mean date of the zero-flow events, on a database of 452 rivers in European and in Mediterranean countries outside Europe, with varying degrees of intermittence. In addition, the relationships between flow intermittence and climate are investigated using the Standardized Precipitation Evapotranspiration Index (SPEI) and six climate indices describing large scale atmospheric circulation. Results indicated a strong spatial variability of the seasonal patterns of intermittence and the annual and seasonal number of zero-flow days, which highlights 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, in particular 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 weak 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.
Highlights
In streams and rivers, flow intermittence is characterized by the cessation of flow, followed or not by complete drying of the channels (Datry et al 2017)
There is no clear dependency between the frequency of zero-flow and catchment size, showing that other catchment characteristics, that are not analyzed in the present study, may have a stronger influence on the occurrence of zero-flow days
This study provides the first European-scale assessment of the trends in river intermittence over the last decades
Summary
Flow intermittence is characterized by the cessation of flow, followed or not by complete drying of the channels (Datry et al 2017). The spatio-temporal patterns of flow intermittence can be extremely variable depending on climatic, geologic or topographic contexts (Costigan et al 2017). While many studies have been focused on river low-flows characterization and, in particular, the possible long-term trends due to climate change (e.g., Marx et al, 2018), far less work has been dedicated to intermittent rivers and ephemeral streams. Intermittence characteristics might be strongly influenced by processes operating at small scales, including groundwater-surface water interactions, river transmission losses, frozen surface water, flow reversal, instrument error, natural or human-driven discharge losses (Beaufort et al, 2019, Costigan et al 2017, Zimmer et al, 2020). The probability of flow intermittence in rivers worldwide is likely to increase with the projected rise of temperature in future climate scenarios
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