The study analyzed 30 years of precipitation data in North China using different methods. They found that the amount of rain and snow varied over time, with more precipitation in the 1980s to 1990s and changes in different seasons. Winter had more rain and snow in the 1980s to 1990s, but less in the 21st century. Spring and autumn precipitation stayed more consistent. The amount of rain and snow suddenly changed in 1997 and 2000. The researchers also discovered that the variation in precipitation happened in cycles of 3-4 years.