Moving towards a unified threshold-based hydrological theory through inter-comparison and modelling
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Date
2021
Authors
Ross, Cody
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Abstract
Numerous studies have ascertained detailed descriptions of hydrological processes for individual hillslopes and catchments. These studies have contributed to process understanding and have revealed considerable spatial and process heterogeneity. In hydrology, there is a scarcity of unifying theories to connect findings from individual studies. Thresholds in runoff response have been identified as a potential foundation for a unified theory, as thresholds are emergent properties that integrate spatial and process heterogeneity. However, our understanding of threshold behaviour has limitations. Most threshold research in hydrology focuses on storage thresholds for humid temperate environments and little is known about other types of thresholds or the ubiquity of thresholds for other environments. Additionally, the benefits of evaluating rainfall-runoff models using threshold information have not been determined. Our understanding of threshold behaviour has also been guided by conceptualizations featuring response as a function of a single meteorological factor, which is at odds with research showing a range of controls on hydrologic response. The goal of this thesis was to address these knowledge gaps and to contribute to a unified threshold-based hydrological theory. First, the spatial and temporal variability in rainfall-runoff event dynamics and the influence of fixed and dynamic controls on hydrologic response for 21 sites were assessed. Second, site-specific rainfall-runoff relationships were evaluated for thresholds. Threshold behaviour was observed at 20 out of 21 sites and in addition to rainfall depth, rainfall intensity and evapotranspiration proved to be important controls. Third, the benefits of constraining rainfall-runoff model outputs using threshold information were appraised. This work showed that threshold information can be powerful for identifying model simulations that adequately predict real-world processes. Lastly, the influence of multiple, potentially interacting, meteorological factors on response thresholds was assessed. This analysis showed that meteorological factor interactions can lead to complex, nonlinear hydrological responses that cannot otherwise be observed. Notably, these findings challenge hydrologists to consider a wider range of threshold behaviours. The findings of this thesis bring us closer to a unified threshold-based hydrologic theory and identified knowledge gaps that remain for this theory to be finalized.
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Keywords
Hydrology, Rainfall-runoff analysis, Threshold, Rainfall-runoff modelling, Response surface
Citation
Ross C., Ali G., Spence C., Oswald C., Casson N. (2019). Comparison of event-specific rainfall-runoff responses and their controls in contrasting geographic areas. Hydrological Processes, 1-18. https://doi-org.uml.idm.oclc.org/10.1002/hyp.13460
Ross, C., Ali, G., Spence, C., & Courchesne, F. (2021). Evaluating the ubiquity of thresholds in rainfall-runoff response across contrasting environments. Water Resources Research, 57, e2020WR027498. https://doi.org/10.1029/2020WR027498
Ross, C., Ali, G., Spence, C., & Courchesne, F. (2021). Evaluating the ubiquity of thresholds in rainfall-runoff response across contrasting environments. Water Resources Research, 57, e2020WR027498. https://doi.org/10.1029/2020WR027498