The Paper's chief reporter Liu Dong
November 7th, coinciding with the 24 solar terms of winter. An earlier than usual cold wave, with its wide range and intensity, swept across northern China with a blizzard. Within 24 hours, the Central Meteorological Observatory issued three consecutive blizzard orange warnings and a yellow warning of cold tide at the same time. On the morning of the 7th, the Tianjin Meteorological Observatory upgraded the blizzard orange warning signal to the blizzard red warning.
"The first snow in Beijing is around the end of November, and this year it is more than 20 days ahead." Sun Shao, an associate researcher at the National Climate Center of the China Meteorological Administration, said in an exclusive interview with the www.thepaper.cn.
Sun Shao said that this winter will form a weak to moderate intensity of the "La Niña" event (referring to the phenomenon of large-scale abnormal cooling of the seawater in the equatorial middle and east Pacific Ocean), affected by this, this winter affects China's cold air activity frequently, the force is strong, the overall temperature in the central and eastern regions is mainly cold, the cold and warm fluctuations in the season are large, and the precipitation is generally distributed in the north and south. Therefore, the probability of a phased extreme cooling event in China this year is higher than that of the usual year.
China is located in the southeast of Eurasia, the west is located inland, the east is bordered by the Pacific Ocean, the monsoon phenomenon is obvious, the climate type is complex and diverse, and it is one of the countries most seriously affected by catastrophic weather in the world.
Since the beginning of this year, China has encountered a wide range of cold waves and wind cooling events, sandstorms, heavy rains, high temperatures and extreme heavy rainfall weather.
According to the statistics of the Meteorological Disaster Database of the National Climate Center, meteorological disasters in the past 30 years (1991-2020) have brought an average of 3,039 deaths (including disappearances) and direct economic losses of 258.4 billion yuan to China every year. Under the background of rapid economic development, the direct economic losses caused by meteorological disasters continue to rise, with direct economic losses reaching 368.1 billion yuan in 2020.
Sun Shao has long been engaged in climate change, extreme events and disaster risk research, and a recent study published in Advances in Climate Change Research explores the potential risks posed by China's major urban agglomerations facing extreme heat and extreme precipitation events in the next 30 years. Studies have shown that in the next 30 years, the frequency of extreme heat and extreme precipitation events in eastern China will continue to rise, and urban climate risks will continue to increase.
In addition to China, this year's global frequency of extreme weather also highlights the importance of focusing on climate change issues. "At present, there is still controversy in the academic circles about whether global warming will lead to the occurrence of El Niño and La Niña events, but in recent years, the frequent occurrence of catastrophic weather such as extreme heat and extreme precipitation around the world has become an indisputable fact, and we are likely to encounter unprecedented extreme weather and climate events in the future." Sun Shao said.
The content of sun shao's dialogue with the surging news is summarized as follows for the benefit of readers.
The Paper: Can you tell us about your research results?
Sun Shao: Starting from the three greenhouse gas emission scenarios and population growth scenarios of high, medium and low, this study estimates the trend of high temperature and heavy rain events in eastern China from 2021 to 2050 (divided into three sub-regions of Beijing-Tianjin-Hebei-Lu, Jiangsu-Zhejiang-Shanghai and Fujian-Guangdong-Qiong), revealing the potential population risk level of 89 major cities in these areas affected by high temperatures and heavy rainstorms.
The main conclusions of the study found that the frequency of high temperature events in southern Hebei, western Shanxi, western Jiangsu and western Guangdong is expected to increase significantly in the next 30 years. Even under the most desirable low-emission scenario (reaching the Paris Agreement's 2°C temperature target and achieving carbon neutrality by 2060), the average number of hot days in eastern China will rise from 9.3 days per year in the historical base period to 16.4 (±1.8) days, of which 10% of the country's land area will face more than 30 days of hot weather (above 35°C).
Under a medium-emission scenario (i.e., maintaining current emission levels), the number of heat days would increase by more than 50 per cent in 50 of the 89 cities in the eastern region, with 37 cities increasing by more than 100 per cent. Combined with the population growth scenario simulation, it is expected that the risk of high temperature population in the Beijing-Tianjin-Hebei-Lu region will double on the basis of the current situation around 2050, while the Jiangsu, Zhejiang, Shanghai and Fujian-Guangdong-Qiong regions will increase by 63% and 42% respectively. Attribution analysis shows that climate change is the main reason for the increase in high temperature risk, with factor contribution rates of more than 80%, while population growth contributes less than 10%, and the frequency of extreme precipitation events in China's southeast coastal cities is expected to increase in the next 30 years, but the increase is lower than that of high temperature events. Under the low emission scenario, the average number of days of heavy precipitation (daily precipitation ≥20 mm) in eastern China increased from 16.5 days per year in the base period to 17.9 (±0.3) days, and the land area affected by heavy precipitation of more than 30 days per year expanded from 4.4% to 10.2%, of which the rising trend in the Fujian-Guangdong-Qiong region was the most significant.
Under a medium emissions scenario, 63 of the 89 cities in the eastern region would see an increase in the number of heavy precipitation days by more than 10 percent, with 16 of them increasing by more than 20 percent. Combined with population scenario simulation, it is expected that the population risk caused by heavy precipitation in eastern China will increase by 23% around 2050, of which the population risk of 22 cities such as Dongguan, Shenzhen, Shantou, Foshan and Zhongshan will increase by more than 30% compared with the historical benchmark period.
The study shows that under the influence of urban expansion and agglomeration effects in coastal areas, the population and wealth of eastern China will continue to grow in the future, and the increase in extreme events and the superposition of urban expansion will lead to the three major metropolitan areas in eastern China becoming hot spots for the socio-economic impact of climate change, which urgently needs to be paid great attention to by decision-makers.
The Paper: What is the background of your research?
Sun Shao: Climate change will affect all walks of life, such as urban operation, human health, energy supply, transportation, and agricultural production, and the adverse effects of the future are what we often call risks. Our study focused on the eastern metropolitan areas, where the socio-economic agglomeration is most concentrated, and the population will continue to migrate to the eastern megacities in the future, and the size of these large cities will further expand, resulting in an increasing risk exposure, or the number of disaster victims.
It is already an indisputable fact that global warming will lead to an increase in extreme weather and climate events. The question is how much the frequency of extreme events will increase, where the increase is most pronounced, and how much potential impact it will have on the social economy in the future.
Based on historical observations, our study quantitatively estimates the frequency of future high temperature events and heavy precipitation events in 89 major economically developed cities in eastern China, and refers to the simulation of future urban population growth, revealing the changing trend of potential urban risks and the contributing factors behind them.
Rescue people after extreme rainfall in Zhengzhou, Henan.
The Paper: According to the Paris Agreement, the average global warming we are now emphasizing is controlled within 2 degrees Celsius, preferably 1.5 degrees Celsius, what does this have to do with the daily lives of ordinary people?
Sun Shao: First of all, it should be clear that the global average temperature itself should be a very stable value, just like the temperature of one of our cities, although there are large fluctuations during the year, the average value of the whole year is relatively stable. If this average increases by 2°C, it means that the increase in the maximum temperature is likely to exceed 2°C. In fact, it is often the extremes rather than the averages that really affect the socioeconomy, and the changes in this extremes tend to be more pronounced than the average.
In the future, climate warming will lead to a significant shortening of the recurrence period of extreme high temperature events, such as the historical 5-year high temperature heat wave weather becomes once every 1 to 2 years, and may also be accompanied by multi-dimensional changes such as duration, scope of impact, time of occurrence, and even unprecedented extreme events, which will have a more serious impact on social and economic development.
The Paper: The global warming has already reached 1.2 degrees Celsius, and it may be broken through 1.5 degrees Celsius in the future in less than 2030, does this mean that the probability and intensity of extreme weather and climate events in the next 10 years are likely to increase on a large scale?
Sun Shao: In recent decades, global temperatures have been rising in fluctuating conditions. As I said earlier, this is a relatively stable value, but the El Niño and La Niña events that occur during the year, as well as volcanic eruptions and solar activity, will also have a certain impact on this value, about ±0.2 °C. Therefore, a temperature rise of more than 1.5 °C in a given year does not mean that the temperature control target has failed, which needs to be made clear.
It is foreseeable that in the process of carbon peaking in the future, the probability of extreme events is likely to increase, and it may increase especially in some hot cities. The association between the increase in extreme heat and extreme precipitation and climate warming is the clearest. However, in addition, some studies have shown that the occurrence of catastrophic weather such as typhoons and droughts has also changed significantly, such as the northward shift of typhoon paths and the increase in drought intensity.
The Paper: This summer, Taiwan encountered extreme heat, drought caused by water shortage, coupled with the lack of power generation, several difficulties put together, and the entire social operation was greatly affected. Is it possible that this phenomenon will happen in other parts of China?
Sun Shao: We call this situation a "compound extreme event," which leads to a significant amplification of the intensity of the disaster. When Taiwan suffered an extreme drought this spring, South China, especially most of Guangdong, also suffered from meteorological droughts of moderate intensity or greater. This is the result of a significantly higher temperature, more sunshine hours, and a seriously low precipitation in the early stage. This drought has adversely affected spring planting, forest fire prevention, and domestic production water, but we have alleviated the drought to a certain extent through artificial rain increase operations, and the drought has gradually eased after the flood. A similar situation occurred in 2011 and 2002.
The amplification effect of this compound event is a hot issue in our current research, and it is also a very critical issue. In addition to the high temperature and drought composite events, China's eastern coastal areas have also appeared in the basin high water level, extreme precipitation and typhoon storm surge composite events, high water level top support effect led to water drainage can not be drained, flooding of rivers overflow, as well as the impact of storm surge and extreme sea level, in such a multi-disaster species of extreme situation how do we deal with? How can meteorological and hydrological models simulate compound and cascading effects in such extreme events? These problems need to be solved urgently, and they are also the difficulties in the current research.
The Paper: Is it possible for a complex extreme weather event to occur in a city with tens of millions of people like Beijing and Shanghai?
Sun Shao: It is entirely possible. In history, Beijing has suffered exceptionally heavy rainstorms in 2016, 2012 and 2011, which not only triggered urban flood disasters, but also caused secondary disasters such as flash floods and mudslides in mountainous areas, causing major losses. And the compound events of high temperatures and droughts you mentioned, Beijing experienced in 2017, 2015 and 2010.
Shanghai's geographical location determines that it has the conditions for the complex flood I mentioned earlier, that is, the combination of "extreme high tide level + extreme precipitation + river flood", in fact, in 2013 and 2008, Shanghai has suffered from exceptionally heavy rainstorms, resulting in urban waterlogging and traffic obstruction, but Shanghai's disaster defense capabilities, especially for emergencies, are strong, so there are no particularly significant casualties, and the last serious flood dates back to 1998. For high temperature and drought compound events, Shanghai also suffered in 2018 and 2015, but it was still able to ensure the supply of water resources by diverting and diverting water, which greatly alleviated the adverse effects of high temperature and drought.
Therefore, we usually refer to the extreme event as the result of characterizing the intensity of the event itself, and the catastrophic impact also depends on the exposure and vulnerability of the disaster recipient, as well as the city's adaptability and emergency management level, which is the result of a complex system.
The Paper: People in coastal areas are more concerned about typhoons, what is the relationship between typhoons and climate change?
Sun Shao: Warming will provide more energy for typhoons, so we observed that under the condition that the total number of typhoons generated is basically unchanged, the number of strong typhoons has increased, the rainfall has increased, and the time spent on land has also increased. In addition, in recent years, the number of typhoons that have landed in China has shown an increasing trend, and the scope of influence has gradually shifted northward, and in September 2020, there have been three consecutive typhoons in the northeast region in half a month, which may be a trend in the impact of climate change on the typhoon path, but it is too early to draw conclusions.
The Paper: There are several typhoons along the coast of Guangdong this year, from formation to landfall is very fast, it seems that it was just formed yesterday, tomorrow the day after tomorrow, the speed of movement is very fast, is this a new feature?
Sun Shao: The location of typhoon generation is related to the El Niño and La Niña events. Usually in El Niño years, typhoons in the northwest Pacific Ocean form easterly, so the probability of developing into a strong typhoon is also greater. In the La Niña year, the typhoon's generation position is far to the west, so it feels that the interval from generation to landfall is shorter. There is no clear evidence that climate change will affect the speed at which typhoons move. Another point that needs to be clear is that the current ability to monitor and forecast typhoons is very strong, and paying attention to the landing site and intensity of typhoons in advance can greatly prevent risks.
The Paper: In the context of the increase in extreme weather and climate events caused by global climate change, has there been a new demand for meteorological disaster risk management?
Sun Shao: At this stage, the academic community's refined simulation and prediction theory and technology for extreme weather and climate events are not yet mature, and most of the existing studies are estimating the macro trends of the global or national scale under future scenarios, and the simulation ability of typical regions and key areas to encounter extreme weather and climate impacts is still lacking.
In addition to improving the monitoring, forecasting and early warning capabilities of extreme weather and climate events, it is also necessary to strengthen the public's disaster science education. In the process of carrying out the national comprehensive disaster risk census, the meteorological department should further clarify the number of hidden dangers of disaster risks, identify the resilience of key areas, scientifically assess the level of meteorological disaster risk in the whole country and each region, and formulate a scientific and practical comprehensive risk zoning of meteorological disasters, so as to reduce the disaster risks caused by extreme events to the greatest extent and provide strong scientific and technological support for ensuring high-quality economic and social development.
The Paper: The concepts of climate change mitigation and adaptation are still unfamiliar to many Chinese. For example, what kind of changes does the future increase in hot weather mean for them?
Sun Shao: Mitigation mainly refers to reducing greenhouse gas emissions, such as using more clean energy such as solar energy and wind energy, improving energy efficiency, and reducing primary energy consumption. But the life of greenhouse gases such as carbon dioxide in the atmosphere is very long, so global warming is also inertia, not that today does not emit greenhouse gases tomorrow will stop warming. Of course, we can shorten this process by increasing carbon sinks through afforestation, as well as technical means such as carbon capture and storage. But in any case, mitigation requires long-term persistence to be effective, while adaptation is more realistic and urgent. Especially for the vast number of developing countries, through cooperation in the research and development of adaptation technologies and the sharing of practical experience, we can improve the ability to prevent climate risks in a shorter period of time, mitigate the adverse effects of climate change, and achieve sustainable socio-economic development.
The main impact of high temperature heat wave weather is the city's energy supply and human health risks. Higher temperatures also speed up the water cycle, bringing more extreme precipitation events, exacerbating the potential risk of urban waterlogging, river flooding and related geological hazards.
For the public, on the one hand, we advocate green and low-carbon travel, to contribute to the slowdown of climate warming, on the other hand, when paying attention to the high temperature warning issued by the meteorological department, we should stop outdoor work activities in time, take heat prevention and cooling measures, and pay attention to preventing fire risks.
Finally, I would like to take this opportunity to remind everyone that now that the summer high temperature has passed, although the world is warming, but under the influence of the Twin Peaks La Niña event this year, the probability of extreme cooling events in winter is still higher than that of the perennial, and it is necessary to prepare in advance, especially to deal with the preparation of complex extreme events such as low temperature rain, snow, ice and wind, properly reserve daily necessities, pay attention to the medium and long-term weather forecast of the destination before traveling, do a good job of traffic route planning, and try to avoid the adverse effects of cold wave weather.
Editor-in-Charge: Zhang Wuwei
Proofreader: Ding Xiao