The study looked at how human activities like farming and irrigation affect the water cycle on land. They used a computer model to simulate different scenarios and found that historical land changes have reduced water loss from plants and increased river flow. Irrigation can decrease river flow if water is taken from local sources, but can increase it if water is brought in from elsewhere. Climate change is expected to decrease water loss and river flow, while expanding farmland will have the opposite effect. In some areas, future water use for farming will increase due to warmer and drier conditions.