Investigating runoff formation dynamics: field observations at Cape Fear experimental plot.

In this paper, we explore the dynamics of surface runoff formation in an outdoor experimental plot, Cape Fear, by reporting the relationships among rainfall, runoff, and soil moisture for 101 rainfall-runoff events observed in the time span of more than five years (January 2014-March 2019). Cape Fear is a recently developed 7 × 7 m2 experimental plot that combines features from both small scale facilities and catchment-scale experimental hillslopes, thus leveraging observation of major hydrological variables at high temporal and spatial resolution. Despite the small dimension and simplicity of the plot, the relations among hydrological variables are unexpectedly quite spread. Experimental results seem to suggest that Cape Fear runoff response presents an increasing and non-linear relationship with rainfall, with a surface runoff coefficient increasing for higher rainfall. Direct runoff apparently increases with soil moisture, while initial abstraction seems not to be influenced by rainfall and is found to decrease with increasing soil moisture. Observations suggest that complex interactions between soil moisture conditions and rainfall pattern properties modulate the plot response.