The researchers analyzed how rainfall is distributed in North China during the rainy season. They found that eastern North China gets more concentrated rainfall compared to the western region. Overall, rainfall, concentration degree, and concentration period have been decreasing over time. The changes started around the late 1970s or early 1980s. The patterns of rainfall concentration and period do not always match, but they follow the same cycle as rainfall. The amount of rainfall affects the distribution of concentration degree. Low pressure from the north and the East-Asian summer monsoon influence rainfall patterns in North China.