The study looked at how rainwater isotopes change as rain falls through the air. By analyzing data from 648 weather stations in the Yangtze River Basin, researchers found that sub-cloud evaporation is stronger during the day than at night. Different regions show varying effects, with the most significant impact in plateau areas. Factors like temperature, humidity, and raindrop size influence the evaporation process. Overall, sub-cloud evaporation is most noticeable when rainfall is light, temperature is high, vapor pressure is low, humidity is moderate, and raindrops are small to medium-sized.