A new University of California San Diego study uncovers a hidden driver of global crop vulnerability: the origin of rainfall itself.

The paper, “Crop water origins and hydroclimate vulnerability of global croplands,” was published in Nature Sustainability.

The research traces atmospheric moisture back to its source—whether it evaporated from the ocean or from land surfaces such as soil, lakes and forests. When the sun heats these surfaces, water turns into vapor, rises into the atmosphere, and later falls again as rain.