Hierarchical climate-driven dynamics of the active channel length in temporary streams

Abstract

Looking across a landscape, river networks appear deceptively static. However, flowing streams expand and contract following ever-changing hydrological conditions of the surrounding environment. Despite the ecological and biogeochemical value of rivers with discontinuous flow, deciphering the temporary nature of streams and quantifying their extent remains challenging. Using a unique observational dataset spanning diverse geomorphoclimatic settings, we demonstrate the existence of a general hierarchical structuring of river network dynamics. Specifically, temporary stream activation follows a fixed and repeatable sequence, in which the least persistent sections activate only when the most persistent ones are already flowing. This hierarchical phenomenon not only facilitates monitoring activities, but enables the development of a general mathematical framework that elucidates how climate drives temporal variations in the active stream length. As the climate gets drier, the average fraction of the flowing network decreases while its relative variability increases. Our study provides a novel conceptual basis for characterizing temporary streams and quantifying their ecological and biogeochemical impacts.

Technical note: Analyzing river network dynamics and the active length–discharge relationship using water presence sensors

“…While the average drainage density of our study catchment (D d = 2.22 km −1 ) is in line with that of other sites where similar analyses were conducted (Jensen et al, 2018;Botter et al, 2021;Senatore et al, 2021), the internal distribution of the channel network is uneven. The analysis of a highresolution DTM indicates that the hydrographic network of the upper Valfredda, here seen as the sum of permanent and temporary reaches, directly drains 65 % of the total contributing area (1.7 km 2 out of 2.6 km 2 ).…”

On the Relation Between Active Network Length and Catchment Discharge

“…Of these surveys, 14 were performed when discharge measurements were not available (July-October 2018, August 2020 and August-September 2021), while a total of 16 synchronous observations of active length and discharge were gathered. For more info about the catchment and the empirical activities carried out therein, the reader is referred to Durighetto et al ( 2020) and Botter et al (2021). A local persistency map was constructed on the basis of the field surveys (Figure 4c), and the Weibull plotting position method was used to construct the empirical cumulative distributions of L and Q (Figures 4a and 4d).…”

Dynamic Clusters to Infer Topologic Controls on Environmental Transport of River Networks

“…The dynamic connectivity framework presented here can be generalized to interrogate the impact of other relevant parameters (e.g., channel geometry, varying flow velocities, and heterogeneous precipitation patterns) on flux transport and aggregation, allowing us to explore the compound effects of those parameters together with topology in the phenomena and scenarios discussed above. A particularly pertinent application of this framework could arise by incorporating the ephemerality (i.e., persistence of streamflow) of the streams to understand the river response in the face of the spatial heterogeneity introduced by the local ecohydrology of the basin (Botter et al., 2021). This phenomenon can induce a significant impact on the hierarchical aggregation of streamflow, which can be further interpreted in conjunction with the topology via the proposed framework.…”