Guest speaker: Yuan Xing, Professor, School of hydrology and water resources engineering, Nanjing University of information technology
Interviewer: Lin Wen, correspondent of China Meteorological News
Current view: the risk of sudden drought in China may increase significantly in the future. By the middle of this century, the risk of sudden drought in Guizhou, Guangxi, Guangdong, Zhejiang and other humid provinces in the South will increase by 40%, while the risk of sudden drought in semi-arid areas in the north will decrease; the increase of sudden drought events is mainly caused by human greenhouse gas emissions, accounting for 77%.
Compared with the traditional drought, sudden drought develops more rapidly and has a shorter forecast period. Due to the strong and strong emergency, the sudden drought may cause incalculable harm to the ecosystem, agricultural production and domestic water, and it is still unable to establish an effective monitoring and early warning means.
The risk of sudden drought in China is on the rise
According to the report released by the World Resources Institute in 2019, about one quarter of the world's population is facing a crisis of extreme water shortage. China's per capita water resources account for less than 1 / 4 of the world average, and it is also one of the countries with the most deficient per capita water resources in the world.
Dried up rivers and lakes, withered vegetation, Limited drinking water, reduced grain production Drought has been a threat to human society. What's more, under the influence of global climate change, the areas affected by drought are quietly changing, and the original humid areas in China may have frequent sudden drought events.
"Generally speaking, drought is a slowly developing climate phenomenon, which is often caused by the lack of precipitation. It will take months or even longer to reach the maximum intensity and range." Yuan Xing, Dean and professor of the school of hydrology and water resources engineering, Nanjing University of information technology, said that under the joint effect of abnormal high temperature and precipitation deficit, the local soil moisture will be continuously lost and evapotranspiration will increase. This kind of drought event with rapid development, short prediction period, high intensity and strong destructive is called "sudden drought".
Through five years of research, Yuan Xing and his collaborators established a set of index system and method to identify the sudden drought, and made a quantitative analysis of the causes and trends of the sudden drought in China and Africa. Relevant research results have been published in the Journal of nature for many times.
"We define the time range of sudden drought in 15-60 days, and its most significant feature is rapid development." Yuan Xing said. In 2012, the sudden drought in the middle of the United States caused billions of dollars of economic losses; in 2013, the sudden drought in the middle and lower reaches of the Yangtze River in China not only led to crop disaster in many provinces (municipalities directly under the central government), but also caused difficulties in water supply.
According to the model calculation, Yuan Xing and his collaborators predict that by the middle of this century, the risk of sudden drought will increase by 40% in Guizhou, Guangxi, Guangdong, Zhejiang and other humid areas in the south, but decrease in the semi-arid areas in the north. On the whole, the risk of sudden drought in China is on the rise in the future.
"South waterlogging and north drought" is gradually changing
Why is the risk of sudden drought increased in the traditional humid and semi humid areas, but decreased in the arid and semi-arid areas?
Yuan Xing said that during the same period of hot rain in most parts of eastern China, hot weather often occurs in the rainy season. In addition, there is sufficient water vapor in the humid and semi humid areas. When there is less rain in the rainy season, the high temperature heat wave will accelerate the loss of water; the vegetation in the wetter areas is lush, and when there is no water, the plants can draw water from the deep soil, which is conducive to the increase of evaporation and emission, and it is easy to form a sudden drought.
"China's sudden drought is more likely to occur in wetter areas, which has a lot to do with global climate change." Yuan Xing explained that global warming has increased the variability of many hydrometeorological elements, and drought and flood are more likely to occur. At the same time, the increase of greenhouse gases changes the intensity of atmospheric external radiation. On the one hand, it brings more high-temperature heat waves to accelerate the evaporation and emission of moisture in humid areas; on the other hand, the increase of external radiation also changes the distribution of clouds, seasonal rainfall becomes more and more unstable, and then changes the traditional regional precipitation distribution.
"We used to say that China was wet in the South and dry in the north, but this phenomenon is gradually changing." Yuan Xing said. According to the forecast results of the fifth report of the Intergovernmental Panel on climate change (IPCC) and the latest data analysis of the sixth coupling model comparison plan, the arid areas in the north of China will become more and more humid, while the humid areas in the South will become more and more dry. "This is also consistent with the trend of sudden drought calculated by us, although the change of South flood and north drought is also closely related to the natural rate of climate change."
"In the context of climate change, the growth trend of China's sudden drought events is very obvious, which is not changed by the temporary warming and slowing down caused by natural phenomena." Yuan Xing gave an example. After the disappearance of a strong El Nino phenomenon at the end of the 20th century, the global average temperature rise slowed down, but the rising trend of the sudden drought event increased three times, "which is closely related to the decrease of soil moisture and the increase of evapotranspiration at the interdecadal and interannual scales."
"The impact of human activities on sudden drought is significant." The results of Yuan Xing's study show that 77% of them are due to climate change caused by greenhouse gas emissions, and the risk of sudden drought exposure will increase with the population growth. "In some areas, sudden drought may become a new normal."
　　
It is an urgent task to set up prediction model
Compared with general drought, the impact of sudden drought on production and life may be greater. "The sudden drought happened very fast, which gave us a short response time and was difficult to deal with in time. Moreover, the sudden drought often occurs in the summer in the relatively humid areas. At this time, the attention of these areas is more focused on flood prevention and lack of preparation for dealing with the sudden drought. " Yuan Xing believes that in addition to the negative impact on human society, the local ecosystem is also relatively more vulnerable in the case of sudden drought.
There are mature models for general drought monitoring and forecasting, but there is not a set of models in the world to accurately predict the occurrence of a sudden drought event. "At present, the research on sudden drought is still in its infancy. It is imperative to further clarify the characteristics and formation mechanism of sudden drought, so as to develop a prediction model to cope with it." Yuan Xing said that at present, the team's climate hydrological coupling model can predict the occurrence trend of sudden drought in a long time scale under the condition of global warming, but it is still difficult to realize the real-time forecast of sudden drought. "The current short-term weather forecast and long-term climate forecast are relatively good, but the 10-30 day extended period forecast is still a worldwide problem, and the sudden drought often occurs at this time In between. Therefore, efforts should be made to develop high-resolution earth system models to provide more reliable scientific tools for dealing with extreme events in a changing environment. "
As for the impact of sudden drought on plant growth and natural ecology, and how to make objective evaluation, more experts and scholars from different disciplines and departments need to cooperate to tackle key problems, carry out more extensive and in-depth research, and establish corresponding early warning system, so as to better carry out the prevention and control of sudden drought.
"Of course, energy conservation and emission reduction are essential." Yuan Xing said that human activities have a great impact on global warming. "Only by reducing carbon emissions and slowing down the trend of global warming, can we reduce the threat of drought and other natural disasters to human society."
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