Where does the evapotranspiration that rises from forests and grasslands come back down as rain? This was the question that Ruud van der Ent asked as a hydrology graduate student. He wondered if he could make a map of the world that would show this flow of moisture around the world. Van der Ent worked with his professor, the renowned Hubert Savenije to make this map. They published this in a paper called “Origin and fate of atmospheric moisture over continents”. … This is the map they made. It shows where evaporation that goes up, will become rain again on the same continent. … I was really happy when I managed to track down Professor Ruud van der Ent, and he agreed to do this interview. Below is an edited excerpt from the interview.