China's nearly 500 years drought and flood disaster online map of the rain waterlogging types of the Yangtze River Basin and North China in Southern China.

Drought: A meteorological disaster caused by a harsh or abnormal drought. Generally speaking, due to insufficient soil moisture, crop water balance is destroyed, and production is reduced or cropped, resulting in food problems.

Waterlog: Due to excessive local precipitation, surface runoff cannot be eliminated in time, and water accumulation in farmland exceeds the ability of crops to withstand flooding, causing disasters in agricultural production. The reason for the crop yield reduction is that the depth of the water is too large, and the time is too long, so that the air in the soil is discharged one after another, causing insufficient oxygen in the roots of the crop, difficulty in breathing in the roots, and producing toxic and harmful substances such as ethanol, thereby affecting crop growth and even cause crop death.