Abstract
An experimental soil tank (12 m long × 1.5 m wide × 1.5 m deep) equipped with a spatially distributed instrument network was designed to conduct the artificial rainfall-runoff experiments. Soil moisture (SM), precipitation, surface runoff (SR) and subsurface runoff (SSR) were continuously monitored. A total of 32 rainfall-runoff events were analyzed to investigate the non-linear patterns of rainfall-runoff response and estimate the impact of antecedent soil moisture (ASM) on runoff formation. Results suggested that ASM had a significant impact on runoff at this plot scale, and a moisture threshold-like value which was close to field capacity existed in the relationship between soil water content and event-based runoff coefficient (φe), SSR and SSR/SR. A non-linear relationship between antecedent soil moisture index (ASI) that represented the initial storage capacity of the soil tank and total runoff was also observed. Response times of SR and SM to rainfall showed a marked variability under different conditions. Under wet conditions, SM at 10 cm started to increase prior to SR on average, whereas it responds slower than SR under dry conditions due to the effect of water repellency. The predominant contributor to SR generation for all events is the Hortonian overland flow (HOF). There is a hysteretic behavior between subsurface runoff flow and soil moisture with a switch in the hysteretic loop direction based on the wetness conditions prior to the event.
Highlights
Nonlinearity in the spatially and temporally complicated hydrologic responses, is widely discussed in the hydrology community [1,2,3]
There is a hysteretic behavior between subsurface runoff flow and soil moisture with a switch in the hysteretic loop direction based on the wetness conditions prior to the event
We investigate the rainfall-runoff response from three aspects, i.e., precipitation, soil moisture (SM)
Summary
Nonlinearity in the spatially and temporally complicated hydrologic responses, is widely discussed in the hydrology community [1,2,3]. The typical nonlinearity in the runoff response is the combined effects of the surface runoff process, the antecedent soil moisture condition, and the way precipitation intensity affects the subsurface process. Regarding interactions of antecedent wetness conditions, various rainfall features (e.g., intensity and duration) and topography properties (e.g., soil type and soil depth) [4,5], non-linear behavior is frequently discussed as influencing surface and subsurface runoff generation processes at hillslope [6,7] and catchment scales [8]. Soil moisture (SM) has great influences on the rainfall-runoff responses [5,10,11,12,13,14] and is non-linearly related to runoff generation [4,15]. Work by Western and Grayson [16] showed that SR was a threshold process controlled by catchment wetness conditions, with runoff coefficients
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