Floods in China, COVID-19, and climate change.

China has made substantial progress regarding COVID-19 control, as the local transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has almost been stopped. However, a serious natural disaster, flooding, unfortunately threatened the lives and homes of people in 27 provinces across central and southern China in July, 2020. Starting on June 2, 2020, authorities in China issued alerts for heavy rainfall for 41 consecutive days. The average precipitation in areas along the Yangtze River has reached the highest level since 1961. As of August 13, at least 219 people had been killed, 0·82 million people needed emergency assistance, 4·01 million people were evacuated, and 63·46 million people were affected by the flooding. Flooding has destroyed nearly 0·4 million homes and damaged 5 million hectares of farmland. According to the Ministry of Emergency Management of China, it is estimated that direct economic losses exceed US$25 billion.

Floods are among the most frequent natural disasters in China. It has been estimated that flooding in China between 1950 and 2018 killed more than 282 737 people and damaged 6 billion hectares of land, and that flooding directly cost approximately $6000 billion between 1990 and 2018. However, the indirect effect of floods was not considered in this estimation of costs. The area of land damaged by flooding each year since 1950 shows an increasing trend, which suggests that the potential impact of floods is also increasing, although mortality directly associated with flooding has been decreasing (appendix p 1).

Climate change could severely alter the risk of floods over large regional and time scales. Changes in precipitation and temperature are among the most notable climatic characteristics that could increase the risk of floods. Most floods in China, including the ongoing flooding in 2020, are caused by extreme precipitation. The average intensity, quantity, and duration of precipitation in southern China this year are among the highest in China since 1961. Drainage basin conditions and the soil status are both affected by precipitation and temperature and are also associated with the increasing risk of floods. Moreover, El Niño Southern Oscillation, Pacific Decadal Oscillation, and atmospheric circulation patterns might influence the volume of precipitation and slow-moving cyclones, which eventually cause severe flooding.

Health effects could occur directly through contact with flood waters, including drowning and injuries from flood-related events (eg, building collapse and damage, electrocution, fire; appendix p 2). Although deaths directly caused by floods decreased between 1950 and 2018 in China (appendix p 1), the magnitude of the indirect health effects is largely unknown. There are increased risks of aggravation of, and deaths from, cardiovascular disease and diabetes after flooding, possibly due to interrupted health services or social support systems. It has been estimated that mortality in populations affected by flooding might increase by up to 50% in the first year after a flood. Importantly, floods increase the risk of communicable disease outbreaks and infections (eg, leptospirosis, hepatitis and gastrointestinal disease, cutaneous and respiratory infections), especially in areas with poor hygiene and population displacement. Contaminants in floodwater (eg, sewage, human and animal faeces, fertilisers, organic waste, toxic chemicals) could lead to infections of the eye and skin and could increase the risk of exposure to poisonous material. Floods could also indirectly facilitate the transmission of water-borne and vector-borne diseases by expanding the number and range of vector habitats. It is also not clear how the floods in 2020 are affecting the physical and mental health of those infected with SARS-CoV-2.

Measures should be initiated to reduce the effects of floods. Effective flood protection requires both structural and non-structural measures. Structural flood protection measures are considered a leading solution to prevent the effects of flooding worldwide, including flood control levees that prevent flooding of adjacent areas and limit the flow of the river, reservoirs that act as flow balancers, floodways that discharge excess flood water to ensure the safety of dams, diversions of waterways, and many others. Non-structural flood protection measures are considered a good complement to structural flood protection measures and can be divided into three categories: avoiding inappropriate use of floodplains and modifying susceptibility to flood damage (eg, via development policies); enhancing preparedness and resilience to flooding (eg, education, flood insurance, tax adjustments); and non-structural flood protection measures that aim to compensate for the drawbacks of structural measures (eg, increasing vegetative cover to reduce erosion). These non-structural flood protection measures focus on changing human behaviour. For individuals, there are many ways to prevent and mitigate flood hazards, such as monitoring the news and their surroundings, elevating electrical appliances, preparing adequate supplies (eg, drinking water, cash, food), finding places to evacuate to, and planning travel routes to allow rapid evacuation.

According to the contribution of Working Group II to the Intergovernmental Panel on Climate Change's Fifth Assessment Report, global flood risk will increase in the future. In a high-end climate scenario, with high population growth and high greenhouse gas emissions, flooding is projected to affect an average of 2·4 million additional people and cost an additional 3 billion Euros per year. In this scenario, at an average global temperature increase of 4°C, the largest increases in flood risks would be in the USA, Asia, and Europe. By the end of the current century, China is projected to be affected the most by flooding, with 40 million people affected and 110 billion Euros of damage per year. Without immediate and unprecedented measures, climate change will result in more heavy flooding, leading to great health and economic impacts, particularly in the context of COVID-19. The world needs to prepare now to mitigate and handle future flooding.