Abstract

There are two contrasting hypotheses on whether fluvial fans need specific climate conditions to form. Deduction of climatic and tectonic signals from landscapes and the sedimentary record is a key aim in geology and geomorphology. It is thus of great interest to obtain recognition criteria for specific climate changes in the sedimentary record in general, and fluvial fans in particular, because they may form the bulk of the continental fluvial record. The hypothesis that links fluvial fan occurrence to climate specifically indicates precipitation variability as a key control, because it promotes streamflow variability, channel instability, and avulsions, which are the key processes involved in fluvial fan formation. Here, we tested this hypothesis by quantitative analyses of discharge patterns from 68 fan-forming rivers that have a global distribution. Using an ensemble of dimensionless metrics, we show that 75% of the fan-forming rivers in this data set have a high discharge variability. We further analyzed down-fan changes in discharge variability and discuss the nature of discharge variability in different hydroclimates as a function of intra- and interannual precipitation fluctuations. We also examined the fan-forming rivers with moderate to low discharge variability and concluded that although river discharge variability strongly promotes fluvial fan formation, fluvial fans may also be formed by rivers with a moderate or low discharge variability if other favorable conditions that promote avulsions occur.

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