Floods in many places occur in the rainy season (for example, floods in China mostly occur in summer), and the air mobility in the rainy season is generally strong, which makes the spread of germs wide and fast, further promoting the outbreak of plague or infectious diseases.
In the middle and low latitudes, floods are mostly caused by rainfall. The river basin is large and controlled by river networks, lakes and reservoirs. When the flood peaks formed by different rainfall of different tributaries converge to the main stream, the flood processes of tributaries often overlap with each other, forming a flood peak with relatively long fluctuation.
Extended data
Storm flood and snowmelt flood in river flood are closely related to weather situation and climate change, and have obvious seasonality. In China, heavy rains and floods often occur in summer and autumn, which are generally called summer floods and autumn floods. Snowmelt floods often occur in spring, commonly known as spring flood or peach flood.
Because this kind of flood occurs every year with the arrival of the season, it has obvious periodicity. Because there are many factors that affect the flood, and the combination of various factors is very different, the flood size in the same basin varies greatly in different years. In some years, catastrophic floods may occur, and in some years, ordinary floods may occur.
This difference reflects the randomness of different floods. From the analysis of long series of data, this kind of interannual flood has certain statistical regularity, that is, the probability of catastrophic flood is few, while the probability of ordinary flood is many.