The researchers studied the humidity levels in the Yellow River source regions since 1961. They found that the humidity index has been decreasing overall, with wetter periods in the past and drier periods in recent years. However, since 2003, there has been an increase in precipitation and humidity, leading to warmer and wetter conditions. The main factors affecting humidity are precipitation, sunshine hours, and humidity itself. Overall, the surface humidity index has increased in spring and winter but decreased in summer and autumn over the past 49 years.