The study looked at how rainfall affects erosion on purple soil slopes. They did experiments with different slopes and rainfall intensities. They found that the way runoff is generated on these slopes is mainly through saturation. The amount of runoff on the surface and underground changes depending on the slope and rainfall intensity. More underground runoff leads to more erosion, especially on steeper slopes. This means that underground runoff plays a big role in causing erosion on these slopes, more than surface runoff. This finding is important for managing erosion on purple soil slopes.