Where and when is water moving in soil? Incorporating spatiotemporal variability of subsurface flows to improve hydrological modelling

Understanding soil water dynamics at different scales is essential for hydrological modelling of future scenarios in which the frequency of droughts, wildfires, and flooding events is expected to increase. Nevertheless, accounting for the spatiotemporal variability of soil moisture in order to predict realistic subsurface water flows (SSWF) and improve hydrological modelling remains a challenge. Given the complexity of addressing hydrological processes, spatially-variable soil physical properties are frequently lumped and treated as constants when modelling, limiting the representation of soil structure dynamics. Since soil water retention (SWR) is derived from the soil structure and its physical properties, hydrological models are rather distant from predicting its spatiotemporal variability at field conditions. Spectral analysis has recently emerged as a promising method for disentangling the spatiotemporal scales at which hydrological processes operate in soils. This proposal aims to improve predictions of the spatiotemporal variability in SSWF and contribute to a better understanding of its impact on hydrological processes. We hypothesize that a physically-based approach to developing a dynamic parameterisation will better represent soil structural behaviour in hydrological modelling. To do so, we will first describe the effect of soil structure dynamics and soil physical properties using a combination of laboratory and field-based approaches. Second, the SSWF spatiotemporal variability in field conditions will be determined using spectral analysis and an inverse modelling method. Third, the SSWF analysis will be linked to soil physical properties to develop dynamic parameterisation. Finally, the physically-based dynamic parameterisation will be assessed using the HYDRUS-2D model to predict SSWF.