Staff Research Highlight - Water sources and threshold behaviors of streamflow generation in a mountain headwater catchment
Chen, X., Yu, Z., Yi, P., Chen, P., Hwang, H.-T., Sudicky, E. A., & Simonovic, S. P. (2024). Water sources and threshold behaviors of streamflow generation in a mountain headwater catchment. In Journal of Hydrology (Vol. 644, p. 132117). Elsevier BV. https://doi.org/10.1016/j.jhydrol.2024.132117
“Only recently have isotopes been utilized for evaluating physics-based models such as HydroGeoSphere.”
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We’re pleased to highlight this publication, co-authored by Aquanty personnel (including senior scientist Dr. Hyoun-Tae Hwang, and Aquanty co-founder Dr. Ed Sudicky).
Fig. 1. (a) Sampling locations of the study area in the southeast of China. (b) Landscape photo of Mukeng catchment and sampling processes of rain, soil and stream water.
In this study, researchers focused on the Mukeng headwater catchment in eastern China, conducting an integrated analysis of streamflow generation mechanisms during 244 rainfall events over a five year period. The study aimed to deepen the understanding of how different water sources contribute to streamflow and to quantify the threshold behaviors in both surface and subsurface flow during rainfall events. Researchers utilized HydroGeoSphere (HGS) for surface and subsurface hydrological modelling combined with isotopic tracing, enabling them to distinguish the spatial and temporal origins of streamflow components and their contributions to runoff.
Findings revealed that indirect runoff—comprised of infiltrated rainfall and shallow soil water—played a dominant role, with indirect water sources reaching up to 81% of total streamflow during rainfall events. The study identified threshold behaviors in the generation of surface and subsurface flow, with 33 mm of rainfall and 9 mm/d intensity as critical thresholds for direct runoff initiation and exfiltration of shallow soil water. Additionally, thresholds of 55 mm for rainfall amount and 12 mm/d for rainfall intensity were observed for shifts in the proportions of infiltrated rainfall and indirect runoff, emphasizing how rainfall dynamics strongly influence the interaction between surface and subsurface water.
These results highlights the importance of accurately representing indirect runoff processes in streamflow modelling, particularly in mountain headwater catchments with high spatiotemporal variability. This research highlights the value of combining hydrological modelling with isotopic tracing to capture complex water source interactions and improve predictions of streamflow generation under varying rainfall conditions.
Abstract:
Numerous studies have analyzed the event-scale rainfall-runoff response of hillslopes and catchments. However, there are still knowledge gaps when it comes to understanding the spatiotemporal sources of headwater catchment runoff and the threshold behaviors of multiple runoff components. The aim of this study is to investigate the complex runoff generation mechanisms for 244 rainfall events in a humid headwater catchment of eastern China over five years (2011–2015). We employ a combined approach of isotopic tracing (δ2H and δ18O) and fully-integrated surface/subsurface flow modelling (HydroGeoSphere) to identify streamflow compositions and how the process chain of “rainfall infiltration, mixing with soil water, and subsequent exfiltration to the hillslope surface” impacts streamflow generation in headwater catchments. Our results show that the streamflow consists of event and pre-event water. Event water is composed of direct runoff from rainfall (2% in the total streamflow) and indirect runoff from infiltrated rainfall (24%). Pre-event water comprises the exfiltrated shallow soil water of indirect runoff (37%) and subsurface flow (37%). The study highlights the significant role of indirect runoff, comprising infiltrated rainfall and pre-event shallow soil water, in streamflow generation, reaching a peak proportion of 81.4% during rainfall events. In addition, we quantify the threshold behaviors (including the generation threshold, and critical threshold from increasing to decreasing state) for surface and subsurface flow, based on the analysis of the non-linear rainfall-runoff relationships observed in the catchment. Results show that rainfall amount of 33 mm and rainfall intensity of 9 mm/d are generation thresholds for direct runoff and critical thresholds for proportion changes of exfiltrated shallow soil water. Critical thresholds of 55 mm for rainfall amount and 12 mm/d for rainfall intensity are identified for proportion changes of infiltrated rainfall and total indirect runoff. Our findings highlight that the combined analysis of hydrological modelling and isotopic tracing provides an effective solution for quantifying the roles of dominant water components in streamflow generation and elucidate the distinct threshold behaviors during rainfall events. Enhancing our comprehension of streamflow origins and their response mechanisms to rainfall events will improve the understanding of streamflow generation in headwater catchments.