Landscapes on the edge: river intermittency in a warming world

Sediment transport in rivers is not uniform through time. Highly intermittent systems, which only transport bedload during the most significant flow events, are particularly sensitive to changes in climate and precipitation patterns. Quantifying river intermittency is critical for assessing how fluvial landscapes will respond to projected changes in precipitation extremes due to climate change, and due to the vulnerability of landscapes and people to fluvial processes. Here, we generate new constraints on recent to modern fluvial intermittency factors – the frequency at which bedload is mobilized in a river – based on field measurements in the Gulf of Corinth, Greece, and Holocene sediment accumulation rates. Results reveal some of the lowest documented intermittency factors to-date, showing Mediterranean rivers can transport their entire annual sediment budget in a rare storm event. Coupling intermittency calculations with historical flood and precipitation data indicates rivers in this environment are dominated by bedload transport during one storm every c. 4 years, associated with rainfall > 50 mm/d and subsequent floods; this hydroclimate is typical of the Mediterranean. Furthermore, climate models predict precipitation extremes will increase across Europe, and the frequency of events that surpass thresholds of sediment transport will increase non-linearly, potentially causing sediment budgets to double by 2100. As the global area of arid land likely to host intermittent rivers also increases, intermittency-dominated landscapes are on the edge of significant geomorphic change, driven by global warming.