A new system was created to model how water moves in the atmosphere and on land. By combining two models, scientists were able to better understand how water flows in a specific river basin in China. They found that a new way of calculating runoff from hillsides improved the accuracy of their predictions. The system showed that groundwater levels in the basin rise in response to heavy rain, with different levels of groundwater found in different areas. Overall, the amount of rain each month determines how much water flows in the rivers, but the flow can vary a lot from month to month.