Recently, many regions across China have endured persistent heavy rainfall, creating a severe flood control situation. What are the characteristics of this year's flood season weather? What can we expect regarding rainfall and flood conditions moving forward? What key considerations should be prioritized for flood prevention and disaster mitigation? Our reporter interviewed several experts.
Since the onset of the main flood season, precipitation in eastern China has generally followed a pattern of heavier rainfall in the north and lighter in the south, with frequent extreme downpours.From July 17 to 22, Henan Province experienced heavy rainfall characterized by high cumulative totals, prolonged duration, intense short-term downpours, and extreme intensity. Nineteen counties and cities recorded daily precipitation exceeding historical records, causing severe impacts.
Chen Lijuan, chief forecaster at the National Climate Center, stated that according to the center's monitoring, since the start of the main flood season (June 1 to July 31), precipitation in eastern China has generally been higher in the north and lower in the south.Precipitation exceeded the long-term average by more than 50% in western Heilongjiang, parts of central and eastern Inner Mongolia, most of Beijing-Tianjin-Hebei, most of Henan, northwestern Shandong, parts of Jiangsu, and northern Zhejiang. In some areas of northern Henan, precipitation was more than double the average, demonstrating extreme variability. Conversely, southern Jiangnan, most of South China, and most of Northwest China experienced significantly below-average precipitation compared to the same period in previous years.
Chen Lijuan noted that from autumn 2020 to spring 2021, a moderate La Niña event occurred in the central and eastern equatorial Pacific, with sea surface temperatures persistently below the long-term average. Typically, summers during the decay phase of a La Niña event favor a northward shift of the Western Pacific subtropical high, directing more moisture toward northern China and resulting in above-average precipitation in those regions.
Furthermore, this year has been marked by pronounced global climate anomalies, particularly in the mid-to-high latitudes of the Northern Hemisphere. Beyond the frequent extreme rainstorms in China's North China and Huanghuai regions, numerous extreme weather and climate events occurred globally between June and July.Chen Lijuan noted that reviewing the global climate situation this year reveals significant climate anomalies in winter, spring, and summer. The continuous emergence of abnormal weather and climate events stems from multiple factors. The direct cause is the combination of atmospheric circulation anomalies, while climate warming has intensified the instability of the climate system, increasing the likelihood of certain extreme weather and climate events.
Global warming has led to more frequent and intense extreme weather and climate events in some regions.
According to the climate statement released by the World Meteorological Organization, the global average temperature in 2020 was approximately 1.2 degrees Celsius higher than the pre-industrial level (the average from 1850 to 1900).The decade from 2011 to 2020 was the warmest on record, with the six warmest years occurring between 2015 and 2020. The Intergovernmental Panel on Climate Change (IPCC) assessment report indicates that global warming has led to more frequent and intense extreme weather and climate events in some regions.
Extensive research confirms that as the climate warms, the atmosphere can hold more water vapor before reaching saturation, increasing the likelihood of extreme heavy precipitation events. Historical data statistics show that the frequency of extreme heat events in the Northern Hemisphere has increased in recent decades, said Dr. Han Zhenyu, a climate change researcher at the National Climate Center.
Han Zhenyu indicated that the latest climate model projections simulate an increase in extreme heat events across most global land areas, while extreme cold events will decrease. Heatwaves will occur more frequently and last longer. As global average surface temperatures rise, extreme precipitation events are likely to intensify and become more frequent in most mid-latitude land regions and humid tropical zones. Precipitation disparities between arid and humid regions, as well as between dry and wet seasons, will widen.Climate projections indicate that under scenarios without greenhouse gas emission controls, by the end of the 21st century, the probability of high-temperature heatwave events in land areas will be 5 to 10 times higher than today, while extreme precipitation in land areas will increase by approximately 20%.As a result, China's extreme precipitation is projected to increase by about 21%, with typhoon-affected areas along the eastern coast doubling. Meanwhile, the area of farmland affected by drought nationwide could increase by more than 1.5 times.
A growing number of meteorological experts have reached a consensus: while not every extreme weather event can be directly attributed to global warming, each occurrence serves as a warning to humanity—climate change, characterized primarily by global warming, poses multifaceted impacts and risks to natural ecosystems and human socioeconomic systems, representing one of the most severe challenges facing the world.Zhou Bing, Chief Climate Services Expert at the National Climate Center, stated.
Forecasts indicate generally unfavorable climate conditions during this year's midsummer, requiring sustained vigilance for flood control
Chen Lijuan explained that the National Climate Center has been issuing rolling forecasts for the flood season since February this year. In the May rolling forecast, the climate outlook was adjusted from "average" to "unfavorable."The late-June forecast for midsummer (July-August) indicates overall unfavorable climate conditions nationwide, with increased extreme weather events and more severe drought and flood disasters. Primary rainfall zones are projected in central-eastern Northwest China, most of Inner Mongolia, North China, Northeast China, Huanghuai, eastern Jianghuai, northeastern Jiangnan, eastern and northern Southwest China, most of Jianghan, and southern South China.
Chen Lijuan stated that according to the National Climate Center's forecast, the East Asian monsoon circulation system affecting China's weather in August will undergo significant phased changes. However, overall conditions will still favor the formation of two precipitation belts—one in the north and one in the south. The northern rain belt will be influenced by fluctuations in the westerly wind trough and ridge, as well as the phased westward and northward expansion of the Western Pacific subtropical high. The southern rain belt will primarily be affected by typhoon activity and the phased southward retreat of the Western Pacific subtropical high.Precipitation is expected to exceed the long-term average in western Xinjiang, Inner Mongolia, Northeast China, North China, eastern Northwest China, northern Huanghuai, Jianghuai, Jiangnan, and northern South China. Two to three tropical cyclones may make landfall or significantly impact South China and the southeast coastal regions.
"We must not relax our vigilance in flood control," Chen Lijuan emphasized.
On July 30, the State Key Laboratory of Disaster Weather convened a symposium on Henan's extreme rainstorms this July. Yu Ruchong, Deputy Director of the China Meteorological Administration, emphasized at the symposium the need to continue scientific research efforts to enhance forecast accuracy and timeliness. He stressed the importance of heightening awareness of the increasing frequency of global extreme weather and climate events, improving response capabilities, and particularly strengthening vigilance against hazardous weather.
China is currently in the critical flood prevention period from late July to early August. Experts recommend that all localities and departments strengthen coordination, intensify inspections to eliminate disaster hazards, reinforce safety measures for key infrastructure, improve early warnings for rainfall, typhoons, flash floods, and mudslides, and meticulously implement all flood prevention and disaster relief measures.For the public, it is essential to stay informed about weather forecasts and warnings while enhancing disaster prevention and mitigation awareness and capabilities. People's Daily (Page 04, August 5, 2021)