When it comes to Earth’s climate system, water is often at the center of the story — whether it’s too much, too little or arriving at the wrong time. And while today’s climate models can tell us how much rain might fall or how humid the air might be, they often can’t answer the simpler, and perhaps more important, question: Where did this water come from?

Now, a new project led by Rice University and the U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR) is changing that. Backed by a grant from the National Science Foundation, the initiative — called SCI-SWIM, short for Sustainable Community Infrastructure for Stable Water Isotope Modeling — will be woven into the NSF NCAR-based Community Earth System Model. It will enable the model to trace water across the entire planet, from the clouds in the sky to the thick ice sheets deep underground. 

SCI-SWIM focuses on stable water isotopes, which are tiny variations in water molecules, specifically oxygen and hydrogen, that shift in predictable ways when water evaporates, condenses, freezes or melts. By following these subtle signals, climate scientists can tell whether a storm drew its moisture from the nearby ocean or from halfway across the globe, separate evaporation from plants versus soil, and gain other crucial insights into water. 

“Stable water isotopes are nature’s tracers,” said Jiang Zhu, project scientist at NSF NCAR and principal investigator of the project. “They give us a direct line of comparison between models and observations, from the rain falling outside your window today to the ice layers recording climate thousands of years ago.”

The project is co-led by Sylvia Dee at Rice and Peter Lauritzen and William Wieder at NSF NCAR. Software implementation efforts are spearheaded by NSF NCAR's William Sacks, Jesse Nusbaumer, and additional collaborators.

For more about SCI-SWIM, see the Rice University press release.

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