section_path: Hydrology/Periodic floods
section_name: Periodic floods
paragraph_text: Periodic floods
  
  Tens of millions of people live in the floodplain of the Yangtze valley, an area that naturally floods every summer and is habitable only because it is protected by river dikes. The floods large enough to overflow the dikes have caused great distress to those who live and farm there. Floods of note include those of 1931, 1954, and 1998.
  
  The 1931 Central China floods or the Central China floods of 1931 were a series of floods that are generally considered among the deadliest natural disasters ever recorded, and almost certainly the deadliest of the 20th century (when pandemics and famines are discounted). Estimates of the total death toll range from 145,000 to between 3.7 million and 4 million. The Yangtze flooded again in 1935, causing great loss of life.
  
  From June to September 1954, the Yangtze River Floods were a series of catastrophic floodings that occurred mostly in Hubei Province. Due to unusually high volume of precipitation as well as an extraordinarily long rainy season in the middle stretch of the Yangtze River late in the spring of 1954, the river started to rise above its usual level in around late June. Despite efforts to open three important flood gates to alleviate the rising water by diverting it, the flood level continued to rise until it hit the historic high of 44.67 m in Jingzhou, Hubei and 29.73 m in Wuhan. The number of dead from this flood was estimated at 33,000, including those who died of plague in the aftermath of the disaster.
  
  The 1998 Yangtze River floods were a series of major floods that lasted from middle of June to the beginning of September 1998 along the Yangtze.
  
  In the summer of 1998, China experienced massive flooding of parts of the Yangtze River, resulting in 3,704 dead, 15 million homeless and $26 billion in economic loss. Other sources report a total loss of 4150 people, and 180 million people were affected. A staggering 25 million acres (100,000 km) were evacuated, 13.3 million houses were damaged or destroyed. The floods caused $26 billion in damages.
  
  The 2016 China floods caused US$22 billion in damages.
  
  In 2020, the Yangtze river saw the heaviest rainfall since 1961, with a 79% increase in June and July compared to the average for the period over the previous 41 years. A new theory suggested that abrupt reduction in emissions of greenhouse gases and aerosols, caused by shutdowns during the COVID-19 pandemic, was a key cause of the intense downpours. Over the past decades rainfall had decreased due to increase of aerosols in the atmosphere, and lower greenhouse gas emissions in 2020 caused the opposite effect – a major increase in rain. Such a dramatic reduction of aerosols caused a dramatic change in the various components of the climate system, but such sudden change of the climate system would be very different from changes in response to continuous but gradual policy-driven emissions reductions.