Streamflow (de)generation - how do streams lose flow?

Streamflow loss is a key process for stream drying and has been studied across various environments and scales. However, there has been little effort to systematically organize processes that drive streamflow loss. We introduce a conceptual framework of “streamflow degeneration” and outline how this framework facilitates the organization of the processes based on subsurface characteristics and settings. The underlying principle for organizing is based on subsurface’s capacity to convey water away from the stream. Using this transport capacity to organize processes of streamflow loss is feasible because it relies on the same principle governing streamflow generation processes. The streamflow degeneration framework includes six distinct streamflow loss processes. We compare how these streamflow loss processes modify a hydrograph along a stream reach under idealized conditions. We call for both field and modeling studies to build on this conceptual framework to define key questions on the significance of streamflow loss. Additionally, we propose various approaches the community may use to answer these questions. The streamflow degeneration framework will help identify commonalities in drying regimes across streams, allowing the generalization of findings from field and modeling studies across various contexts. Organizing streamflow loss according to the streamflow degeneration framework might ultimately lead to the discovery of hydrological laws and the transferability of this understanding of streamflow loss to unstudied reaches.