On the emergence of heavy-tailed streamflow distributions

• Diverse versions of a stochastic model compared in terms of high flow statistics.
• Key role of non-linear storage–discharge to reproduce frequencies of high flows.
• Importance of studying individual recessions to portray the basin hydrologic response.
• Emergence of heavy tails linked to non-linearity of catchment response.
• Implications for floods, riparian vegetation dynamics and sediment transport.

The right tail of streamflow distributions quantifies the occurrence probability of high flows, which play an important role in the dynamics of many eco-hydrological processes and eventually contribute to shape riverine environments. In this paper, the ability of a mechanistic analytical model for streamflow distributions to capture the statistical features of high flows has been investigated. The model couples a stochastic description of soil moisture dynamics with a simplified hydrologic response based on a catchment-scale storage–discharge relationship. Different types of relations between catchment water storage and discharge have been investigated, and alternative methods for parameter estimation have been compared using informal performance metrics and formal model selection criteria. The study highlights the pivotal role of non-linear storage–discharge relations in reproducing observed frequencies of high flows, and reveals the importance of analyzing the behavior of individual events for a reliable characterization of recession parameters. The emergence of heavy-tailed streamflow distributions is mechanistically linked to the degree of non-linearity of the catchment hydrologic response, with implications for the understanding of rivers’ flooding potential and related ecologic and morphological processes.