Landscapes on the edge: solving the river intermittency puzzle

Water and sediment transport in rivers are not uniform through time. In perennial rivers, sediment may be in motion for much of the year. However, intermittent rivers only transport bedload material during the most significant flow events, therefore changes in precipitation patterns have a large impact on these sensitive systems. Understanding intermittency is thus a key challenge in the Earth Sciences due to the vulnerability of landscapes in a changing climate. Here, we generate new constraints on modern fluvial intermittency factors based on field measurements in the Gulf of Corinth, Greece, including hydraulic geometry, sediment grain size and well-constrained Holocene accumulation rates into a closed basin. Results reveal that these rivers are extremely intermittent, requiring only 1 - 5 hours of active bedload transport per year in order to fulfil their annual bedload sediment budgets. Historical data reinforce these results, suggesting that the channels draining into the Gulf are only active in large, infrequent storms associated with rainfall rates > 50 mm/d; this hydroclimate is typical of large areas of Mediterranean landscape. Furthermore, climate models predict precipitation extremes (i.e., storminess) will increase across Europe. Therefore, as the threshold of sediment transport is surpassed more frequently, we predict annual sediment budgets will increase significantly by the year 2100. As storminess increases, source-to-sink dynamics in intermittent river systems across the globe are likely to be the most impacted by environmental change in the near future.