Inverse Estimation of Storage Dynamics Based on a Quasi-Steady State Character of the Waveform Conversion from Rainfall to Stormflow in the Fixed Source Area

Waveform conversion from rainfall to stormflow in headwater catchments is generally characterized by a quasi-steady state represented as a single tank model after the source area has been extended to the entire catchment due to enough amount of rainfall (Tani, Hydrol. Earth Syst. Sci. 17, 2013). Hence, if a functional relationship between the stormflow and storage optimized for the conversion in the fixed source area covering the entire catchment is applied to that for its variable condition with less rainfall amounts, we may inversely examine the storage dynamics such as time or spatial changes in the source area and the water-pressure propagation within it by comparing the assumed application results with the observed rainfall and runoff records. Based on this methodology, we attempted to analyze observed stormflow responses in small headwater catchments to estimate the storage dynamics, and the analyzed results were also examined against hydrometric observations within the soil layer to detect the hydraulic mechanisms of stormflow. This study may have a potential for a re-evaluation of physical backgrounds in lumped conceptual rainfall-runoff models widely used as practical tools for stormflow in active tectonic regions with large-magnitude storms like Japan.