Hydrological signatures of Critical Zone Processes: Developing targets for Critical Zone modeling.

Abstract:

Water fluxes through the Critical Zone (CZ) are ubiquitous, and their behavior has the potential to reveal information about the structure and dynamics of the CZ. Models describing these fluxes implicitly propose hypotheses about the CZ which are encoded in the structure of the models. However, the certainty with which such hypotheses can be tested with observed hydrologic data is challenged by the well-known problem of equifinality – the tendency of multiple models, with very different model structures, to produce equally good representations of observed hydrologic dynamics. The project of modeling the CZ is thus challenged by the need to identify hydrologic signatures that are closely tied to the CZ structure and which could provide a stronger basis for hypothesis testing in model frameworks. Here I present one potential signature based on streamflow recession dynamics and the structure of their variability. Firstly, I present a technique to remove a mathematical artifact that is inherent in power-law representations of streamflow recessions. Secondly, I show that having removed this artifact, intriguing relationships emerge in the recession variability in the rivers near the Eel River Critical Zone Observatory. This relationship is interpreted in terms of how water is partitioned within the CZ. The close relationship between CZ processes and this part of the hydrologic response suggests that co-variation in recession parameters could provide a process-oriented hydrologic signature that CZ models should attempt to emulate.