The researchers studied rainwater in the Guanzhong Plain to understand where the water comes from. They found that rainwater isotopes change with the seasons, being lighter in the wet season and heavier in the dry season. The rainwater in the area comes from a mix of warm, humid air from the southeast and dry, cold air from the west. Most of the rainwater (55%-79%) comes from the ocean, especially in summer, while the rest (21%-45%) comes from local evaporation and inland sources, mainly in winter.