The researchers developed a new method to separate baseflow from rainfall and streamflow data. They used a combination of a general unit hydrograph model and the Green-Ampt infiltration equation to distinguish between surface flow and subsurface flow. By applying this method to real-world case studies, they discovered that the parameters for modeling subsurface flow can vary depending on stream stages. This suggests that the subsurface system is a time-variant linear system, which can even result in negative interflow under certain conditions. This new approach could lead to a better understanding of watershed processes and improve baseflow separation techniques.