The researchers used a computer model called SWAT to predict how much water would run off the land in a river basin. They tested the model in the Subarnarekha river basin and found that it accurately predicted the amount of surface runoff. The model showed that a significant amount of rainwater in the area turns into runoff, which could be captured for irrigation and groundwater recharge. This suggests that building structures to store excess rainwater could be beneficial for the region.