Global climate change is projected to continue and result in prolonged and more intense droughts, which can
increase soil water repellency (SWR). To be able to estimate the consequences of SWR on vadose zone hydrology, it is
important to determine soil hydraulic properties (SHP). Sequential modeling using HYDRUS (2D/3D) was performed on
an experimental field site with artificially imposed drought scenarios (moderately M and severely S stressed) and a control
plot. First, inverse modeling was performed for SHP estimation based on water and ethanol infiltration experimental data, followed by model validation on one selected irrigation event. Finally, hillslope modeling was performed to assess water balance for 2014. Results suggest that prolonged dry periods can increase soil water repellency. Inverse modeling was successfully performed for infiltrating liquids, water and ethanol, with R2 and model efficiency (E) values both > 0.9. SHP derived from the ethanol measurements showed large differences in van Genuchten-Mualem (VGM) parameters for the M and S plots compared to water infiltration experiments. SWR resulted in large saturated hydraulic conductivity (Ks) decrease on the M and S scenarios. After validation of SHP on water content measurements during a selected irrigation event, one year simulations (2014) showed that water repellency increases surface runoff in non-structured soils at hillslopes.
The main objective of this study is to assess the effect of hysteresis of soil hydraulic properties on model predictions of soil water movement in a variably saturated soil. The model predictions are generated by the S1D model, which is based on numerical solution of one-dimensional Richards’ equation. The analysis is made for a loamy sand soil located in a small headwater catchment. The model is used to simulate the development of soil water pressure during three successive vegetation seasons. Three major simulation scenarios are formulated: the first scenario assumes no hysteresis in soil hydraulic properties, the second scenario involves a predefined hypothetical hysteresis, while the third scenario is based on optimized hysteresis, determined through the inverse modeling procedure. The analysis of the simulation results suggests that, in our case, ignoring hysteresis does not lead to any significant deviation of the model predictions from the observed soil water system responses. and Možnosti efektivně matematicky modelovat proudění vody v přirozených půdních formacích omezuje komplikovanost určení půdních hydraulických charakteristik, a to nejen s ohledem na jejich prostorovou a časovou variabilitu, ale také hysterezi. Příspěvek je zaměřen na testování vlivu hystereze na výsledky simulací proudění půdní vody v podmínkách malého horského povodí. Numerický model S1D, řešící Richardsovu rovnici v jednorozměrném tvaru, byl použit k výpočtu sezónního vývoje tlaku půdní vody. V simulacích byla alternativně uvažována hystereze retenční křivky. Odchylky mezi odezvami modelu a měřeními byly minimalizovány optimalizací scaling faktorů. Rozsáhlý srovnávací soubor uskutečněných optimalizací umožnil posoudit rozdíly modelové odezvy dvou hysterezních a jedné nehysterezní varianty a kvantifikovat dopad zanedbání hystereze na přesnost předpovědi modelu. Neuvažování hystereze v našem případě nezhoršuje schopnost modelu popsat změny půdní vlhkosti.